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30 pages, 54589 KiB

Open AccessArticle

How Heat Transfer Indirectly Affects Performance of Algae-Bacteria Raceways

by Francesca Casagli and Olivier Bernard

Microorganisms 2022, 10(8), 1515; https://doi.org/10.3390/microorganisms10081515 - 26 Jul 2022

Cited by 4 | Viewed by 1748

Abstract

Oxygenation in wastewater treatment leads to a high energy demand. High-rate algal-bacterial ponds (HRABP) have often been considered an interesting solution to reduce this energy cost, as the oxygen is provided by microalgae during photosynthesis. These complex dynamic processes are subject to solar [...] Read more.

Oxygenation in wastewater treatment leads to a high energy demand. High-rate algal-bacterial ponds (HRABP) have often been considered an interesting solution to reduce this energy cost, as the oxygen is provided by microalgae during photosynthesis. These complex dynamic processes are subject to solar fluxes and consequently permanent fluctuations in light and temperature. The process efficiency therefore highly depends on the location and the period of the year. In addition, the temperature response can be strongly affected by the process configuration (set-up, water depth). Raised pilot-scale raceways are typically used in experimental campaigns, while raceways lying on the ground are the standard reactor configuration for industrial-scale applications. It is therefore important to assess what the consequences are for the temperature patterns of the different reactor configurations and the water levels. The long-term validated algae-bacteria (ALBA) model was used to represent algae-bacteria dynamics in HRABPs. The model was previously validated over 600 days of outdoor measurements, at two different locations and for the four seasons. However, the first version of the model, like all the existing algae-bacteria models, was not fully predictive, since, to be run, it required the measurement of water temperature. The ALBA model was therefore updated, coupling it with a physical model that predicts the temperature evolution in the HRABP. A heat transfer model was developed, and it was able to accurately predict the temperature during the year (with a standard error of 1.5

^{°}

C). The full predictive model, using the temperature predictions, degraded the model’s predictive performances by less than 3%. N

_{2}

O predictions were affected by

\pm 7

%, highlighting the sensitivity of nitrification to temperature The temperature response for two different process configurations were then compared. The biological process can be subjected to different temperature dynamics, with more extreme temperature events when the raceway does not lie on the ground and for thinner depths. Such a situation is more likely to lead to culture crashes. Full article

(This article belongs to the Special Issue Microbes for Production of Biofuels and Bio-Products)

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21 pages, 13673 KiB

Open AccessArticle

Genome Analysis of Celeribacter sp. PS-C1 Isolated from Sekinchan Beach in Selangor, Malaysia, Reveals Its β-Glucosidase and Licheninase Activities

by Nurfatini Radzlin, Amira Suriaty Yaakop, Kian Mau Goh, Kok Jun Liew, Iffah Izzati Zakaria and Ummirul Mukminin Kahar

Microorganisms 2022, 10(2), 410; https://doi.org/10.3390/microorganisms10020410 - 10 Feb 2022

Cited by 4 | Viewed by 2124

Abstract

A halophilic marine bacterial strain, PS-C1, was isolated from Sekinchan beach in Selangor, Malaysia. The 16S rRNA gene sequence analysis indicated that strain PS-C1 was associated with the genus Celeribacter. To date, there have been no reports on enzymes from the genus [...] Read more.

A halophilic marine bacterial strain, PS-C1, was isolated from Sekinchan beach in Selangor, Malaysia. The 16S rRNA gene sequence analysis indicated that strain PS-C1 was associated with the genus Celeribacter. To date, there have been no reports on enzymes from the genus Celeribacter. The present study reports on the cellular features of Celeribacter sp. PS-C1, its annotated genome sequence, and comparative genome analyses of Celeribacter glycoside hydrolase (GH) enzymes. The genome of strain PS-C1 has a size of 3.87 Mbp and a G+C content of 59.10%, and contains 3739 protein-coding genes. Detailed analysis using the Carbohydrate-Active enZYmes (CAZy) database revealed that Celeribacter genomes harboured at least 12 putative genes encoding industrially important GHs that are grouped as cellulases, β-glucanases, hemicellulases, and starch-degrading enzymes. Herein, the potential applications of these enzymes are discussed. Furthermore, the activities of two types of GHs (β-glucosidase and licheninase) in strain PS-C1 were demonstrated. These findings suggest that strain PS-C1 could be a reservoir of novel GH enzymes for lignocellulosic biomass degradation. Full article

(This article belongs to the Special Issue Microbes for Production of Biofuels and Bio-Products)

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15 pages, 1911 KiB

Open AccessArticle

Physiological Effects of 2-Bromoethanesulfonate on Hydrogenotrophic Pure and Mixed Cultures

by Washington Logroño, Marcell Nikolausz, Hauke Harms and Sabine Kleinsteuber

Microorganisms 2022, 10(2), 355; https://doi.org/10.3390/microorganisms10020355 - 3 Feb 2022

Cited by 9 | Viewed by 2310

Abstract

Mixed or pure cultures can be used for biomethanation of hydrogen. Sodium 2-bromoethanesulfonate (BES) is an inhibitor of methanogenesis used to investigate competing reactions like homoacetogenesis in mixed cultures. To understand the effect of BES on the hydrogenotrophic metabolism in a biomethanation process, [...] Read more.

Mixed or pure cultures can be used for biomethanation of hydrogen. Sodium 2-bromoethanesulfonate (BES) is an inhibitor of methanogenesis used to investigate competing reactions like homoacetogenesis in mixed cultures. To understand the effect of BES on the hydrogenotrophic metabolism in a biomethanation process, anaerobic granules from a wastewater treatment plant, a hydrogenotrophic enrichment culture, and pure cultures of Methanococcus maripaludis and Methanobacterium formicicum were incubated under H₂/CO₂ headspace in the presence or absence of BES, and the turnover of H₂, CO₂, CH₄, formate and acetate was analyzed. Anaerobic granules produced the highest amount of formate after 24 h of incubation in the presence of BES. Treating the enrichment culture with BES led to the accumulation of formate. M. maripaludis produced more formate than M. formicicum when treated with BES. The non-inhibited methanogenic communities produced small amounts of formate whereas the pure cultures did not. The highest amount of acetate was produced by the anaerobic granules concomitantly with formate consumption. These results indicate that formate is an important intermediate of hydrogenotrophic metabolism accumulating upon methanogenesis inhibition. Full article

(This article belongs to the Special Issue Microbes for Production of Biofuels and Bio-Products)

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16 pages, 1561 KiB

Open AccessArticle

Biorefinery Concept Employing Bacillus coagulans: LX-Lignin and L-(+)-Lactic Acid from Lignocellulose

by Linda Schroedter, Friedrich Streffer, Katrin Streffer, Peter Unger and Joachim Venus

Microorganisms 2021, 9(9), 1810; https://doi.org/10.3390/microorganisms9091810 - 25 Aug 2021

Cited by 12 | Viewed by 2442

Abstract

A new biorefinery concept is proposed that integrates the novel LX-Pretreatment with the fermentative production of L-(+)-lactic acid. Lignocellulose was chosen as a substrate that does not compete with the provision of food or feed. Furthermore, it contains lignin, a promising new chemical [...] Read more.

A new biorefinery concept is proposed that integrates the novel LX-Pretreatment with the fermentative production of L-(+)-lactic acid. Lignocellulose was chosen as a substrate that does not compete with the provision of food or feed. Furthermore, it contains lignin, a promising new chemical building material which is the largest renewable source for aromatic compounds. Two substrates were investigated: rye straw (RS) as a residue from agriculture, as well as the fibrous digestate of an anaerobic biogas plant operated with energy corn (DCS). Besides the prior production of biogas from energy corn, chemically exploitable LX-Lignin was produced from both sources, creating a product with a low carbohydrate and ash content (90.3% and 88.2% of acid insoluble lignin). Regarding the cellulose fraction of the biomass, enzymatic hydrolysis and fermentation experiments were conducted, comparing a separate (SHF), simultaneous (SSF) and prehydrolyzed simultaneous saccharification and fermentation (PSSF) approach. For this purpose, thermophilic B. coagulans 14-300 was utilized, reaching 38.0 g L⁻¹ LA in 32 h SSF from pretreated RS and 18.3 g L⁻¹ LA in 30 h PSSF from pretreated DCS with optical purities of 99%. Full article

(This article belongs to the Special Issue Microbes for Production of Biofuels and Bio-Products)

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13 pages, 2807 KiB

Open AccessArticle

Two-Stage Fermentation of Lipomyces starkeyi for Production of Microbial Lipids and Biodiesel

by Le Zhang, Ee Yang Lim, Kai-Chee Loh, Yanjun Dai and Yen Wah Tong

Microorganisms 2021, 9(8), 1724; https://doi.org/10.3390/microorganisms9081724 - 13 Aug 2021

Cited by 12 | Viewed by 3141

Abstract

The high operating cost is currently a limitation to industrialize microbial lipids production by the yeast Lipomyces starkeyi. To explore economic fermentation technology, the two-stage fermentation of Lipomyces starkeyi using yeast extract peptone dextrose (YPD) medium, orange peel (OP) hydrolysate medium, and [...] Read more.

The high operating cost is currently a limitation to industrialize microbial lipids production by the yeast Lipomyces starkeyi. To explore economic fermentation technology, the two-stage fermentation of Lipomyces starkeyi using yeast extract peptone dextrose (YPD) medium, orange peel (OP) hydrolysate medium, and their mixed medium were investigated for seven days by monitoring OD₆₀₀ values, pH values, cell growth status, C/N ratios, total carbon concentration, total nitrogen concentration, residual sugar concentration, lipid content, lipid titer, and fatty acids profiles of lipids. The results showed that two-stage fermentation with YPD and 50% YPD + 50% OP medium contributed to lipid accumulation, leading to larger internal lipid droplets in the yeast cells. However, the cells in pure OP hydrolysate grew abnormally, showing skinny and angular shapes. Compared to the one-stage fermentation, the two-stage fermentation enhanced lipid contents by 18.5%, 27.1%, and 21.4% in the flasks with YPD medium, OP medium, and 50%YPD + 50%OP medium, and enhanced the lipid titer by 77.8%, 13.6%, and 63.0%, respectively. The microbial lipids obtained from both one-stage and two-stage fermentation showed no significant difference in fatty acid compositions, which were mainly dominated by palmitic acid (33.36–38.43%) and oleic acid (46.6–48.12%). Hence, a mixture of commercial medium and lignocellulosic biomass hydrolysate could be a promising option to balance the operating cost and lipid production. Full article

(This article belongs to the Special Issue Microbes for Production of Biofuels and Bio-Products)

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11 pages, 1230 KiB

Open AccessArticle

A Yarrowia lipolytica Strain Engineered for Pyomelanin Production

by Macarena Larroude, Djamila Onésime, Olivier Rué, Jean-Marc Nicaud and Tristan Rossignol

Microorganisms 2021, 9(4), 838; https://doi.org/10.3390/microorganisms9040838 - 14 Apr 2021

Cited by 10 | Viewed by 3308

Abstract

The yeast Yarrowia lipolytica naturally produces pyomelanin. This pigment accumulates in the extracellular environment following the autoxidation and polymerization of homogentisic acid, a metabolite derived from aromatic amino acids. In this study, we used a chassis strain optimized to produce aromatic amino acids [...] Read more.

The yeast Yarrowia lipolytica naturally produces pyomelanin. This pigment accumulates in the extracellular environment following the autoxidation and polymerization of homogentisic acid, a metabolite derived from aromatic amino acids. In this study, we used a chassis strain optimized to produce aromatic amino acids for the de novo overproduction of pyomelanin. The gene 4HPPD, which encodes an enzyme involved in homogentisic acid synthesis (4-hydroxyphenylpyruvic acid dioxygenase), was characterized and overexpressed in the chassis strain with up to three copies, leading to pyomelanin yields of 4.5 g/L. Homogentisic acid is derived from tyrosine. When engineered strains were grown in a phenylalanine-supplemented medium, pyomelanin production increased, revealing that the yeast could convert phenylalanine to tyrosine, or that the homogentisic acid pathway is strongly induced by phenylalanine. Full article

(This article belongs to the Special Issue Microbes for Production of Biofuels and Bio-Products)

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14 pages, 817 KiB

Open AccessArticle

Metabolome Analysis of Constituents in Membrane Vesicles for Clostridium thermocellum Growth Stimulation

by Shunsuke Ichikawa, Yoichiro Tsuge and Shuichi Karita

Microorganisms 2021, 9(3), 593; https://doi.org/10.3390/microorganisms9030593 - 13 Mar 2021

Cited by 2 | Viewed by 2497

Abstract

The cultivation of the cellulolytic bacterium, Clostridium thermocellum, can have cost-effective cellulosic biomass utilizations, such as consolidated bioprocessing, simultaneous biological enzyme production and saccharification. However, these processes require a longer cultivation term of approximately 1 week. We demonstrate that constituents of the [...] Read more.

The cultivation of the cellulolytic bacterium, Clostridium thermocellum, can have cost-effective cellulosic biomass utilizations, such as consolidated bioprocessing, simultaneous biological enzyme production and saccharification. However, these processes require a longer cultivation term of approximately 1 week. We demonstrate that constituents of the C. thermocellum membrane vesicle fraction significantly promoted the growth rate of C. thermocellum. Similarly, cell-free Bacillus subtilis broth was able to increase C. thermocellum growth rate, while several B. subtilis single-gene deletion mutants, e.g., yxeJ, yxeH, ahpC, yxdK, iolF, decreased the growth stimulation ability. Metabolome analysis revealed signal compounds for cell–cell communication in the C. thermocellum membrane vesicle fraction (ethyl 2-decenoate, ethyl 4-decenoate, and 2-dodecenoic acid) and B. subtilis broth (nicotinamide, indole-3-carboxaldehyde, urocanic acid, nopaline, and 6-paradol). These findings suggest that the constituents in membrane vesicles from C. thermocellum and B. subtilis could promote C. thermocellum growth, leading to improved efficiency of cellulosic biomass utilization. Full article

(This article belongs to the Special Issue Microbes for Production of Biofuels and Bio-Products)

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13 pages, 2223 KiB

Open AccessArticle

Increasing the Production of Volatile Fatty Acids from Corn Stover Using Bioaugmentation of a Mixed Rumen Culture with Homoacetogenic Bacteria

by Nanditha Murali, Keerthi Srinivas and Birgitte K. Ahring

Microorganisms 2021, 9(2), 337; https://doi.org/10.3390/microorganisms9020337 - 8 Feb 2021

Cited by 18 | Viewed by 2663

Abstract

Volatile fatty acids (VFA) are industrially versatile chemicals and have a major market. Although currently produced from petrochemicals, chemical industries are moving towards more bio-based VFA produced from abundant, cheap and renewable sources such as lignocellulosic biomass. In this study, we examined the [...] Read more.

Volatile fatty acids (VFA) are industrially versatile chemicals and have a major market. Although currently produced from petrochemicals, chemical industries are moving towards more bio-based VFA produced from abundant, cheap and renewable sources such as lignocellulosic biomass. In this study, we examined the effect of bioaugmentation with homoacetogenic bacteria for increasing VFA production in lignocellulose fermentation process. The central hypothesis of this study was that inhibition of methanogenesis in an in vitro rumen bioreactor fed with lignocellulosic biomass hydrolysate increases the hydrogen partial pressure, which can be redirected towards increased VFA production, particularly acetic acid, through targeted bioaugmentation with known homoacetogenic bacteria. In this study, methanogenesis during ruminal fermentation of wet exploded corn stover was initially inhibited with 10 mM of 2-bromoethanesulfonate (BES), followed by bioaugmentation with either Acetitomaculum ruminis and Acetobacterium woodii in two separate bioreactors. During the inhibition phase, we found that addition of BES decreased the acetic acid yield by 24%, while increasing headspace hydrogen from 1% to 60%. After bioaugmentation, the headspace hydrogen was consumed in both bioreactors and the concentration of acetic acids increased 45% when A. ruminis was added and 70% with A. woodii added. This paper demonstrates that mixed microbial fermentation can be manipulated to increase VFA production through bioaugmentation. Full article

(This article belongs to the Special Issue Microbes for Production of Biofuels and Bio-Products)

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19 pages, 26175 KiB

Open AccessArticle

Deletion of the Aspergillus niger Pro-Protein Processing Protease Gene kexB Results in a pH-Dependent Morphological Transition during Submerged Cultivations and Increases Cell Wall Chitin Content

by Tim M. van Leeuwe, Mark Arentshorst, Gabriel Forn-Cuní, Nicholas Geoffrion, Adrian Tsang, Frank Delvigne, Annemarie H. Meijer, Arthur F. J. Ram and Peter J. Punt

Microorganisms 2020, 8(12), 1918; https://doi.org/10.3390/microorganisms8121918 - 2 Dec 2020

Cited by 5 | Viewed by 2357

Abstract

There is a growing interest in the use of post-fermentation mycelial waste to obtain cell wall chitin as an added-value product. In the pursuit to identify suitable production strains that can be used for post-fermentation cell wall harvesting, we turned to an Aspergillus [...] Read more.

There is a growing interest in the use of post-fermentation mycelial waste to obtain cell wall chitin as an added-value product. In the pursuit to identify suitable production strains that can be used for post-fermentation cell wall harvesting, we turned to an Aspergillus niger strain in which the kexB gene was deleted. Previous work has shown that the deletion of kexB causes hyper-branching and thicker cell walls, traits that may be beneficial for the reduction in fermentation viscosity and lysis. Hyper-branching of ∆kexB was previously found to be pH-dependent on solid medium at pH 6.0, but was absent at pH 5.0. This phenotype was reported to be less pronounced during submerged growth. Here, we show a series of controlled batch cultivations at a pH range of 5, 5.5, and 6 to examine the pellet phenotype of ΔkexB in liquid medium. Morphological analysis showed that ΔkexB formed wild type-like pellets at pH 5.0, whereas the hyper-branching ΔkexB phenotype was found at pH 6.0. The transition of phenotypic plasticity was found in cultivations at pH 5.5, seen as an intermediate phenotype. Analyzing the cell walls of ΔkexB from these controlled pH-conditions showed an increase in chitin content compared to the wild type across all three pH values. Surprisingly, the increase in chitin content was found to be irrespective of the hyper-branching morphology. Evidence for alterations in cell wall make-up are corroborated by transcriptional analysis that showed a significant cell wall stress response in addition to the upregulation of genes encoding other unrelated cell wall biosynthetic genes. Full article

(This article belongs to the Special Issue Microbes for Production of Biofuels and Bio-Products)

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Review

Jump to: Research

24 pages, 896 KiB

Open AccessReview

Fungal Cell Factories for Efficient and Sustainable Production of Proteins and Peptides

by Mette Lübeck and Peter Stephensen Lübeck

Microorganisms 2022, 10(4), 753; https://doi.org/10.3390/microorganisms10040753 - 30 Mar 2022

Cited by 50 | Viewed by 10868

Abstract

Filamentous fungi are a large and diverse taxonomically group of microorganisms found in all habitats worldwide. They grow as a network of cells called hyphae. Since filamentous fungi live in very diverse habitats, they produce different enzymes to degrade material for their living, [...] Read more.

Filamentous fungi are a large and diverse taxonomically group of microorganisms found in all habitats worldwide. They grow as a network of cells called hyphae. Since filamentous fungi live in very diverse habitats, they produce different enzymes to degrade material for their living, for example hydrolytic enzymes to degrade various kinds of biomasses. Moreover, they produce defense proteins (antimicrobial peptides) and proteins for attaching surfaces (hydrophobins). Many of them are easy to cultivate in different known setups (submerged fermentation and solid-state fermentation) and their secretion of proteins and enzymes are often much larger than what is seen from yeast and bacteria. Therefore, filamentous fungi are in many industries the preferred production hosts of different proteins and enzymes. Edible fungi have traditionally been used as food, such as mushrooms or in fermented foods. New trends are to use edible fungi to produce myco-protein enriched foods. This review gives an overview of the different kinds of proteins, enzymes, and peptides produced by the most well-known fungi used as cell factories for different purposes and applications. Moreover, we describe some of the challenges that are important to consider when filamentous fungi are optimized as efficient cell factories. Full article

(This article belongs to the Special Issue Microbes for Production of Biofuels and Bio-Products)

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22 pages, 1176 KiB

Open AccessReview

Homo-Acetogens: Their Metabolism and Competitive Relationship with Hydrogenotrophic Methanogens

by Supriya Karekar, Renan Stefanini and Birgitte Ahring

Microorganisms 2022, 10(2), 397; https://doi.org/10.3390/microorganisms10020397 - 8 Feb 2022

Cited by 30 | Viewed by 5506

Abstract

Homo-acetogens are microbes that have the ability to grow on gaseous substrates such as H₂/CO₂/CO and produce acetic acid as the main product of their metabolism through a metabolic process called reductive acetogenesis. These acetogens are dispersed in nature [...] Read more.

Homo-acetogens are microbes that have the ability to grow on gaseous substrates such as H₂/CO₂/CO and produce acetic acid as the main product of their metabolism through a metabolic process called reductive acetogenesis. These acetogens are dispersed in nature and are found to grow in various biotopes on land, water and sediments. They are also commonly found in the gastro-intestinal track of herbivores that rely on a symbiotic relationship with microbes in order to breakdown lignocellulosic biomass to provide the animal with nutrients and energy. For this motive, the fermentation scheme that occurs in the rumen has been described equivalent to a consolidated bioprocessing fermentation for the production of bioproducts derived from livestock. This paper reviews current knowledge of homo-acetogenesis and its potential to improve efficiency in the rumen for production of bioproducts by replacing methanogens, the principal H₂-scavengers in the rumen, thus serving as a form of carbon sink by deviating the formation of methane into bioproducts. In this review, we discuss the main strategies employed by the livestock industry to achieve methanogenesis inhibition, and also explore homo-acetogenic microorganisms and evaluate the members for potential traits and characteristics that may favor competitive advantage over methanogenesis, making them prospective candidates for competing with methanogens in ruminant animals. Full article

(This article belongs to the Special Issue Microbes for Production of Biofuels and Bio-Products)

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13 pages, 569 KiB

Open AccessReview

The Role of Metal Ions in Fungal Organic Acid Accumulation

by Levente Karaffa, Erzsébet Fekete and Christian P. Kubicek

Microorganisms 2021, 9(6), 1267; https://doi.org/10.3390/microorganisms9061267 - 10 Jun 2021

Cited by 16 | Viewed by 3264

Abstract

Organic acid accumulation is probably the best-known example of primary metabolic overflow. Both bacteria and fungi are capable of producing various organic acids in large amounts under certain conditions, but in terms of productivity-and consequently, of commercial importance-fungal platforms are unparalleled. For high [...] Read more.

Organic acid accumulation is probably the best-known example of primary metabolic overflow. Both bacteria and fungi are capable of producing various organic acids in large amounts under certain conditions, but in terms of productivity-and consequently, of commercial importance-fungal platforms are unparalleled. For high product yield, chemical composition of the growth medium is crucial in providing the necessary conditions, of which the concentrations of four of the first-row transition metal elements, manganese (Mn²⁺), iron (Fe²⁺), copper (Cu²⁺) and zinc (Zn²⁺) stand out. In this paper we critically review the biological roles of these ions, the possible biochemical and physiological consequences of their influence on the accumulation of the most important mono-, di- and tricarboxylic as well as sugar acids by fungi, and the metal ion-related aspects of submerged organic acid fermentations, including the necessary instrumental analytics. Since producing conditions are associated with a cell physiology that differs strongly to what is observed under “standard” growth conditions, here we consider papers and patents only in which organic acid accumulation levels achieved at least 60% of the theoretical maximum yield, and the actual trace metal ion concentrations were verified. Full article

(This article belongs to the Special Issue Microbes for Production of Biofuels and Bio-Products)

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25 pages, 2744 KiB

Open AccessReview

Molecular Microbial Community Analysis as an Analysis Tool for Optimal Biogas Production

by Seyedbehnam Hashemi, Sayed Ebrahim Hashemi, Kristian M. Lien and Jacob J. Lamb

Microorganisms 2021, 9(6), 1162; https://doi.org/10.3390/microorganisms9061162 - 28 May 2021

Cited by 10 | Viewed by 4635

Abstract

The microbial diversity in anaerobic digestion (AD) is important because it affects process robustness. High-throughput sequencing offers high-resolution data regarding the microbial diversity and robustness of biological systems including AD; however, to understand the dynamics of microbial processes, knowing the microbial diversity is [...] Read more.

The microbial diversity in anaerobic digestion (AD) is important because it affects process robustness. High-throughput sequencing offers high-resolution data regarding the microbial diversity and robustness of biological systems including AD; however, to understand the dynamics of microbial processes, knowing the microbial diversity is not adequate alone. Advanced meta-omic techniques have been established to determine the activity and interactions among organisms in biological processes like AD. Results of these methods can be used to identify biomarkers for AD states. This can aid a better understanding of system dynamics and be applied to producing comprehensive models for AD. The paper provides valuable knowledge regarding the possibility of integration of molecular methods in AD. Although meta-genomic methods are not suitable for on-line use due to long operating time and high costs, they provide extensive insight into the microbial phylogeny in AD. Meta-proteomics can also be explored in the demonstration projects for failure prediction. However, for these methods to be fully realised in AD, a biomarker database needs to be developed. Full article

(This article belongs to the Special Issue Microbes for Production of Biofuels and Bio-Products)

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14 pages, 470 KiB

Open AccessReview

Challenges and Potential in Increasing Lutein Content in Microalgae

by Yuxiao Xie, Xiaochao Xiong and Shulin Chen

Microorganisms 2021, 9(5), 1068; https://doi.org/10.3390/microorganisms9051068 - 15 May 2021

Cited by 30 | Viewed by 3754

Abstract

Research on enhancing lutein content in microalgae has made significant progress in recent years. However, strategies are needed to address the possible limitations of microalgae as practical lutein producers. The capacity of lutein sequestration may determine the upper limit of cellular lutein content. [...] Read more.

Research on enhancing lutein content in microalgae has made significant progress in recent years. However, strategies are needed to address the possible limitations of microalgae as practical lutein producers. The capacity of lutein sequestration may determine the upper limit of cellular lutein content. The preliminary estimation presented in this work suggests that the lutein sequestration capacity of the light-harvesting complex (LHC) of microalgae is most likely below 2% on the basis of dry cell weight (DCW). Due to its nature as a structural pigment, higher lutein content might interfere with the LHC in fulfilling photosynthetic functions. Storing lutein in a lipophilic environment is a mechanism for achieving high lutein content but several critical barriers must be overcome such as lutein degradation and access to lipid droplet to be stored through esterification. Understanding the mechanisms underlying lipid droplet biogenesis in chloroplasts, as well as carotenoid trafficking through chloroplast membranes and carotenoid esterification, may provide insight for new approaches to achieve high lutein contents in algae. In the meantime, building the machinery for esterification and sequestration of lutein and other hydroxyl-carotenoids in model microorganisms, such as yeast, with synthetic biology technology provides a promising option. Full article

(This article belongs to the Special Issue Microbes for Production of Biofuels and Bio-Products)

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23 pages, 1553 KiB

Open AccessReview

Increasing Solvent Tolerance to Improve Microbial Production of Alcohols, Terpenoids and Aromatics

by Thomas Schalck, Bram Van den Bergh and Jan Michiels

Microorganisms 2021, 9(2), 249; https://doi.org/10.3390/microorganisms9020249 - 26 Jan 2021

Cited by 10 | Viewed by 3434

Abstract

Fuels and polymer precursors are widely used in daily life and in many industrial processes. Although these compounds are mainly derived from petrol, bacteria and yeast can produce them in an environment-friendly way. However, these molecules exhibit toxic solvent properties and reduce cell [...] Read more.

Fuels and polymer precursors are widely used in daily life and in many industrial processes. Although these compounds are mainly derived from petrol, bacteria and yeast can produce them in an environment-friendly way. However, these molecules exhibit toxic solvent properties and reduce cell viability of the microbial producer which inevitably impedes high product titers. Hence, studying how product accumulation affects microbes and understanding how microbial adaptive responses counteract these harmful defects helps to maximize yields. Here, we specifically focus on the mode of toxicity of industry-relevant alcohols, terpenoids and aromatics and the associated stress-response mechanisms, encountered in several relevant bacterial and yeast producers. In practice, integrating heterologous defense mechanisms, overexpressing native stress responses or triggering multiple protection pathways by modifying the transcription machinery or small RNAs (sRNAs) are suitable strategies to improve solvent tolerance. Therefore, tolerance engineering, in combination with metabolic pathway optimization, shows high potential in developing superior microbial producers. Full article

(This article belongs to the Special Issue Microbes for Production of Biofuels and Bio-Products)

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