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A special issue of International Journal of Molecular Sciences (ISSN 1422-0067). This special issue belongs to the section "Materials Science".

Deadline for manuscript submissions: closed (31 December 2016) | Viewed by 45644

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Dr. ChulHee Kang

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Department of Chemistry, School of Chemical Engineering and Bioengineering, School of Molecular Biosciences, Washington State University, Pullman, WA 99164, USA
Interests: monolignol biosynthesis; enzyme structure and function; biodegradation of organic pollutants; cardiotoxicity of synthetic drugs
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Dear Colleagues,

Within the last several years, there has been a rapidly growing interest in developing biofuels. Much of this interest has been spurred by a need to find renewable sources of energy to partially replace petroleum, while mitigating levels of greenhouse gases. So far, biofuel production has been based mainly on Zea mays, which has resulted in several economic and social problems. Therefore, a new strategy and basic research aiming to increase the efficiency of currently applied or alternative methods of manufacturing plant cellulose-based biofuels and of (de)cross-linking cellulose into lignin polymers in the cell wall are needed for the scientific community. New methods are also needed for breeding new biofuel crops and for characterizing biochemical and genetic lignocellulose synthesis and storage processes, so as to support emerging biofuel products with enhanced and manageable lignocellulosic chemical profiles.

Dr. ChulHee Kang
Guest Editor

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Keywords

cellulose/hemicellulose
cell wall composition
lignin and other biomass
monolignol biosynthetic pathway
lignin biosynthesis
cellulose biosynthesis
radical coupling chemistry
peroxidase and laccase
alteration of lignin composition
efficient use of soil nitrogen
the overall environmental impact associated with cellulosic biofuels.
new biofuel crop

Published Papers (5 papers)

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Research

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7098 KiB

Open AccessArticle

Hydrogen Production by a Chlamydomonas reinhardtii Strain with Inducible Expression of Photosystem II

by Khorcheska Batyrova and Patrick C. Hallenbeck

Int. J. Mol. Sci. 2017, 18(3), 647; https://doi.org/10.3390/ijms18030647 - 16 Mar 2017

Cited by 34 | Viewed by 6091

Abstract

Chlamydomonas reinhardtii cy6Nac2.49 is a genetically modified algal strain that activates photosynthesis in a cyclical manner, so that photosynthesis is not active constitutively in the presence of oxygen, but is turned on only in response to a metabolic trigger (anaerobiosis). Here, we further investigated hydrogen production by this strain comparing it with the parental wild-type strain under photoheterotrophic conditions in regular tris-acetate-phosphate (TAP) medium with a 10-h:14-h light/dark regime. Unlike the wild-type, whose level of H₂ production remained low during illumination, H₂ production in the mutant strain increased gradually with each subsequent light period, and by the final light period was significantly higher than the wild-type. The relatively low Photosystem II (PSII) activity of the mutant culture was shown by low fluorescence yield both in the dark (Fv/Fm) and in the light (δF/Fm’) periods. Measurement of oxygen evolution confirmed the low photosynthetic activity of the mutant cells, which gradually accumulated O₂ to a lesser extent than the wild-type, thus allowing the mutant strain to maintain hydrogenase activity over a longer time period and to gradually accumulate H₂ during periods of illumination. Therefore, controllable expression of PSII can be used to increase hydrogen production under nutrient replete conditions, thus avoiding many of the limitations associated with nutrient deprivation approaches sometimes used to promote hydrogen production. Full article

(This article belongs to the Special Issue Biofuel)

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2355 KiB

Open AccessArticle

Co-Production of Fungal Biomass Derived Constituents and Ethanol from Citrus Wastes Free Sugars without Auxiliary Nutrients in Airlift Bioreactor

by Behzad Satari, Keikhosro Karimi, Mohammad J. Taherzadeh and Akram Zamani

Int. J. Mol. Sci. 2016, 17(3), 302; https://doi.org/10.3390/ijms17030302 - 26 Feb 2016

Cited by 43 | Viewed by 9833

Abstract

The potential of two zygomycetes fungi, Mucor indicus and Rhizopus oryzae, in assimilating citrus waste free sugars (CWFS) and producing fungal chitosan, oil, and protein as well as ethanol was investigated. Extraction of free sugars from citrus waste can reduce its environmental impact by decreasing the possibility of wild microorganisms growth and formation of bad odors, a typical problem facing the citrus industries. A total sugar concentration of 25.1 g/L was obtained by water extraction of citrus waste at room temperature, used for fungal cultivation in shake flasks and airlift bioreactor with no additional nutrients. In shake flasks cultivations, the fungi were only able to assimilate glucose, while fructose remained almost intact. In contrast, the cultivation of M. indicus and R. oryzae in the four-liter airlift bioreactor resulted in the consumption of almost all sugars and production of 250 and 280 g fungal biomass per kg of consumed sugar, respectively. These biomasses correspondingly contained 40% and 51% protein and 9.8% and 4.4% oil. Furthermore, the fungal cell walls, obtained after removing the alkali soluble fraction of the fungi, contained 0.61 and 0.69 g chitin and chitosan per g of cell wall for M. indicus and R. oryzae, respectively. Moreover, the maximum ethanol yield of 36% and 18% was obtained from M. indicus and R. oryzae, respectively. Furthermore, that M. indicus grew as clump mycelia in the airlift bioreactor, while R. oryzae formed spherical suspended pellets, is a promising feature towards industrialization of the process. Full article

(This article belongs to the Special Issue Biofuel)

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1299 KiB

Open AccessArticle

Polyphosphate during the Regreening of Chlorella vulgaris under Nitrogen Deficiency

by Fei-Fei Chu, Xiao-Fei Shen, Paul K. S. Lam and Raymond J. Zeng

Int. J. Mol. Sci. 2015, 16(10), 23355-23368; https://doi.org/10.3390/ijms161023355 - 28 Sep 2015

Cited by 15 | Viewed by 5483

Abstract

Polyphosphate (Poly-P) accumulation has been reported in Chlorella vulgaris under nitrogen deficiency conditions with sufficient P supply, and the process has been demonstrated to have great impact on lipid productivity. In this article, the utilization of polyphosphates and the regreening process under N resupplying conditions, especially for lipid production reviving, were investigated. This regreening process was completed within approximately 3–5 days. Polyphosphates were first degraded within 3 days in the regreening process, with and without an external P supply, and the degradation preceded the assimilation of phosphate in the media with an external P offering. Nitrate assimilation was markedly influenced by the starvation of P after polyphosphates were exhausted in the medium without external phosphates, and then the reviving process of biomass and lipid production was strictly impeded. It is, thus, reasonable to assume that simultaneous provision of external N and P is essential for overall biodiesel production revival during the regreening process. Full article

(This article belongs to the Special Issue Biofuel)

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Review

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482 KiB

Open AccessReview

Xylose Fermentation by Saccharomyces cerevisiae: Challenges and Prospects

by Danuza Nogueira Moysés, Viviane Castelo Branco Reis, João Ricardo Moreira de Almeida, Lidia Maria Pepe de Moraes and Fernando Araripe Gonçalves Torres

Int. J. Mol. Sci. 2016, 17(3), 207; https://doi.org/10.3390/ijms17030207 - 25 Feb 2016

Cited by 204 | Viewed by 15827

Abstract

Many years have passed since the first genetically modified Saccharomyces cerevisiae strains capable of fermenting xylose were obtained with the promise of an environmentally sustainable solution for the conversion of the abundant lignocellulosic biomass to ethanol. Several challenges emerged from these first experiences, most of them related to solving redox imbalances, discovering new pathways for xylose utilization, modulation of the expression of genes of the non-oxidative pentose phosphate pathway, and reduction of xylitol formation. Strategies on evolutionary engineering were used to improve fermentation kinetics, but the resulting strains were still far from industrial application. Lignocellulosic hydrolysates proved to have different inhibitors derived from lignin and sugar degradation, along with significant amounts of acetic acid, intrinsically related with biomass deconstruction. This, associated with pH, temperature, high ethanol, and other stress fluctuations presented on large scale fermentations led the search for yeasts with more robust backgrounds, like industrial strains, as engineering targets. Some promising yeasts were obtained both from studies of stress tolerance genes and adaptation on hydrolysates. Since fermentation times on mixed-substrate hydrolysates were still not cost-effective, the more selective search for new or engineered sugar transporters for xylose are still the focus of many recent studies. These challenges, as well as under-appreciated process strategies, will be discussed in this review. Full article

(This article belongs to the Special Issue Biofuel)

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921 KiB

Open AccessReview

Biofuel Production Based on Carbohydrates from Both Brown and Red Macroalgae: Recent Developments in Key Biotechnologies

by Shigeyuki Kawai and Kousaku Murata

Int. J. Mol. Sci. 2016, 17(2), 145; https://doi.org/10.3390/ijms17020145 - 06 Feb 2016

Cited by 67 | Viewed by 7818

Abstract

Marine macroalgae (green, red and brown macroalgae) have attracted attention as an alternative source of renewable biomass for producing both fuels and chemicals due to their high content of suitable carbohydrates and to their advantages over terrestrial biomass. However, except for green macroalgae, which contain relatively easily-fermentable glucans as their major carbohydrates, practical utilization of red and brown macroalgae has been regarded as difficult due to the major carbohydrates (alginate and mannitol of brown macroalgae and 3,6-anhydro-L-galactose of red macroalgae) not being easily fermentable. Recently, several key biotechnologies using microbes have been developed enabling utilization of these brown and red macroalgal carbohydrates as carbon sources for the production of fuels (ethanol). In this review, we focus on these recent developments with emphasis on microbiological biotechnologies. Full article

(This article belongs to the Special Issue Biofuel)

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