Life | June 2013 - Browse Articles

575 KiB

Open AccessArticle

Heterotrophic Protists in Hypersaline Microbial Mats and Deep Hypersaline Basin Water Columns

by Virginia P. Edgcomb and Joan M. Bernhard

Life 2013, 3(2), 346-362; https://doi.org/10.3390/life3020346 - 22 May 2013

Cited by 21 | Viewed by 10717

Although hypersaline environments pose challenges to life because of the low water content (water activity), many such habitats appear to support eukaryotic microbes. This contribution presents brief reviews of our current knowledge on eukaryotes of water-column haloclines and brines from Deep Hypersaline Anoxic Basins (DHABs) of the Eastern Mediterranean, as well as shallow-water hypersaline microbial mats in solar salterns of Guerrero Negro, Mexico and benthic microbialite communities from Hamelin Pool, Shark Bay, Western Australia. New data on eukaryotic diversity from Shark Bay microbialites indicates eukaryotes are more diverse than previously reported. Although this comparison shows that eukaryotic communities in hypersaline habitats with varying physicochemical characteristics are unique, several groups are commonly found, including diverse alveolates, strameonopiles, and fungi, as well as radiolaria. Many eukaryote sequences (SSU) in both regions also have no close homologues in public databases, suggesting that these environments host unique microbial eukaryote assemblages with the potential to enhance our understanding of the capacity of eukaryotes to adapt to hypersaline conditions. Full article

(This article belongs to the Special Issue Extremophiles and Extreme Environments)

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720 KiB

Open AccessArticle

Prebiotic Chemistry: Geochemical Context and Reaction Screening

by Henderson James Cleaves II

Life 2013, 3(2), 331-345; https://doi.org/10.3390/life3020331 - 29 Apr 2013

Cited by 42 | Viewed by 12645

Abstract

The origin of life on Earth is widely believed to have required the reactions of organic compounds and their self- and/or environmental organization. What those compounds were remains open to debate, as do the environment in and process or processes by which they became organized. Prebiotic chemistry is the systematic organized study of these phenomena. It is difficult to study poorly defined phenomena, and research has focused on producing compounds and structures familiar to contemporary biochemistry, which may or may not have been crucial for the origin of life. Given our ignorance, it may be instructive to explore the extreme regions of known and future investigations of prebiotic chemistry, where reactions fail, that will relate them to or exclude them from plausible environments where they could occur. Come critical parameters which most deserve investigation are discussed. Full article

(This article belongs to the Special Issue Prebiotic Chemistry: Chemical Evolution of Organics on the Primitive Earth)

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184 KiB

Open AccessArticle

Is Struvite a Prebiotic Mineral?

by Maheen Gull and Matthew A. Pasek

Life 2013, 3(2), 321-330; https://doi.org/10.3390/life3020321 - 29 Apr 2013

Cited by 24 | Viewed by 9960

Abstract

The prebiotic relevance of mineral struvite, MgNH₄PO₄·6H₂O, was studied experimentally as a phosphorylating reagent and, theoretically, to understand the geochemical requirements for its formation. The effectiveness of phosphorylation by the phosphate mineral, monetite, CaHPO_4, was also studied to compare to the efficiency of struvite. The experiments focused on the phosphorylation reactions of the minerals with organic compounds, such as nucleosides, glycerol and choline chloride, and heat at 75 °C for about 7–8 days and showed up to 28% phosphorylation of glycerol. In contrast, the compositional requirements for the precipitation of struvite are high ammonium and phosphate concentrations, as well as a little Ca²⁺ dissolved in the water. Combined, these requirements suggest that it is not likely that struvite was present in excess on the early Earth to carry out phosphorylation reactions. The present study focuses on the thermodynamic aspects of struvite formation, complementing the results given by Orgel and Handschuh (1973), which were based on the kinetic effects. Full article

(This article belongs to the Special Issue Prebiotic Chemistry: Chemical Evolution of Organics on the Primitive Earth)

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147 KiB

Open AccessReview

Hot Spring Metagenomics

by Olalla López-López, María Esperanza Cerdán and María Isabel González-Siso

Life 2013, 3(2), 308-320; https://doi.org/10.3390/life3020308 - 25 Apr 2013

Cited by 73 | Viewed by 11266

Abstract

Hot springs have been investigated since the XIX century, but isolation and examination of their thermophilic microbial inhabitants did not start until the 1950s. Many thermophilic microorganisms and their viruses have since been discovered, although the real complexity of thermal communities was envisaged when research based on PCR amplification of the 16S rRNA genes arose. Thereafter, the possibility of cloning and sequencing the total environmental DNA, defined as metagenome, and the study of the genes rescued in the metagenomic libraries and assemblies made it possible to gain a more comprehensive understanding of microbial communities—their diversity, structure, the interactions existing between their components, and the factors shaping the nature of these communities. In the last decade, hot springs have been a source of thermophilic enzymes of industrial interest, encouraging further study of the poorly understood diversity of microbial life in these habitats. Full article

(This article belongs to the Special Issue Extremophiles and Extreme Environments)

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699 KiB

Open AccessReview

Magnetotactic Bacteria from Extreme Environments

by Dennis A. Bazylinski and Christopher T. Lefèvre

Life 2013, 3(2), 295-307; https://doi.org/10.3390/life3020295 - 26 Mar 2013

Cited by 41 | Viewed by 10476

Abstract

Magnetotactic bacteria (MTB) represent a diverse collection of motile prokaryotes that biomineralize intracellular, membrane-bounded, tens-of-nanometer-sized crystals of a magnetic mineral called magnetosomes. Magnetosome minerals consist of either magnetite (Fe₃O₄) or greigite (Fe₃S₄) and cause cells to align along the Earth’s geomagnetic field lines as they swim, a trait called magnetotaxis. MTB are known to mainly inhabit the oxic–anoxic interface (OAI) in water columns or sediments of aquatic habitats and it is currently thought that magnetosomes function as a means of making chemotaxis more efficient in locating and maintaining an optimal position for growth and survival at the OAI. Known cultured and uncultured MTB are phylogenetically associated with the Alpha-, Gamma- and Deltaproteobacteria classes of the phylum Proteobacteria, the Nitrospirae phylum and the candidate division OP3, part of the Planctomycetes-Verrucomicrobia-Chlamydiae (PVC) bacterial superphylum. MTB are generally thought to be ubiquitous in aquatic environments as they are cosmopolitan in distribution and have been found in every continent although for years MTB were thought to be restricted to habitats with pH values near neutral and at ambient temperature. Recently, however, moderate thermophilic and alkaliphilic MTB have been described including: an uncultured, moderately thermophilic magnetotactic bacterium present in hot springs in northern Nevada with a probable upper growth limit of about 63 °C; and several strains of obligately alkaliphilic MTB isolated in pure culture from different aquatic habitats in California, including the hypersaline, extremely alkaline Mono Lake, with an optimal growth pH of >9.0. Full article

(This article belongs to the Section Microbiology)

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Life, Volume 3, Issue 2 (June 2013) – 5 articles , Pages 295-362

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