Areps siddiqui etal 2013

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Psychrophiles

ArticleinAnnualReviewofEarthandPlanetarySciencesMay2012

DOI:10.1146/annurev-earth-040610-133514

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KhawarSohailSiddiqui

KingFahdUniversityofPetroleumandMiner

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TimothyWilliams

UNSWAustralia

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MichelleAllen

UNSWAustralia

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RicardoCavicchioli

UNSWAustralia

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EA41CH06-Cavicchioli ARI 7 February 2013 14:43

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PsychrophilesKhawar S. Siddiqui,1 Timothy J. Williams,1

David Wilkins,1 Sheree Yau,1 Michelle A. Allen,1

Mark V. Brown,1,2 Federico M. Lauro,1

and Ricardo Cavicchioli11School of Biotechnology and Biomolecular Sciences and 2Evolution and Ecology ResearchCenter, The University of New South Wales, Sydney, New South Wales 2052, Australia;email: r.cavicchioli@unsw.edu.au

Annu. Rev. Earth Planet. Sci. 2013. 41:6.16.29

The Annual Review of Earth and Planetary Sciences isonline at earth.annualreviews.org

This articles doi:10.1146/annurev-earth-040610-133514

Copyright c 2013 by Annual Reviews.All rights reserved

Keywords

microbial cold adaptation, cold-active enzymes, metagenomics, microbialdiversity, Antarctica

Abstract

Psychrophilic (cold-adapted) microorganisms make a major contributionto Earths biomass and perform critical roles in global biogeochemical cy-cles. The vast extent and environmental diversity of Earths cold biospherehas selected for equally diverse microbial assemblages that can include ar-chaea, bacteria, eucarya, and viruses. Underpinning the important ecologicalroles of psychrophiles are exquisite mechanisms of physiological adaptation.Evolution has also selected for cold-active traits at the level of molecularadaptation, and enzymes from psychrophiles are characterized by specificstructural, functional, and stability properties. These characteristics of en-zymes from psychrophiles not only manifest in efficient low-temperatureactivity, but also result in a flexible protein structure that enables biocatalysisin nonaqueous solvents. In this review, we examine the ecology of Antarcticpsychrophiles, physiological adaptation of psychrophiles, and properties ofcold-adapted proteins, and we provide a view of how these characteristicsinform studies of astrobiology.

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Review in Advance first posted online on February 14, 2013. (Changes may still occur before final publication online and in print.)

Changes may still occur before final publication online and in print

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EA41CH06-Cavicchioli ARI 7 February 2013 14:43

INTRODUCTION

Much of life on Earth has evolved to colonize low-temperature environments. In fact, at tem-peratures permanently below 5C, the cold biosphere represents by far the largest fraction ofthe global biosphere (Feller & Gerday 2003, Cavicchioli 2006, Siddiqui & Cavicchioli 2006,Casanueva et al. 2010, Margesin & Miteva 2011). Consistent with representative size, the coldbiosphere consists of diverse types of environmentsvast tracts of the deep sea, geographically dis-persed alpine regions, geologically specific subterranean caverns, climatically challenged regionsof permafrost, and biogeochemically diverse polar reaches (Figure 1). Proliferating throughoutthese cold realms is a plethora of psychrophilic (cold-adapted) microorganismsarchaea, bacte-ria, eucarya, and viruses. A small proportion of the isolated microorganisms from naturally coldenvironments have a restricted growth temperature range with an upper growth temperature limitless than20C (stenopsychrophile), whereas the majority of isolates have a broader temperaturerange, tolerating warmer temperatures (eurypsychrophile).

Particularly through the application of molecular genetics approaches, most notably small sub-unit ribosomal RNA (SSU rRNA) sequencing, fluorescent in situ hybridization (FISH), and DNAsequencing of whole environmental samples (metagenomics), the cold biosphere has been discov-ered to harbor a diverse range ofmicrobial groups. In recent years, the application ofmetagenomicsand associated meta-functional approaches (metaproteomics and metatranscriptomics) has shedlight on whole microbial community composition dynamics and microbial processes that are be-ing driven by the resident psychrophiles. Genomic, physiological, and biochemical analyses ofpsychrophilic isolates and their cellular components have also gleaned valuable information aboutthe diverse molecular mechanisms of cold adaptation. As a result, whether driven by global ques-tions concerning the impact of ecosystem change onmicrobial communities in cold environments,fundamental studies of molecular structure and function, or biotechnologically driven pursuits ofnovel cold-active biocatalysts, the field of psychrophiles has made great advances.

This review aims to cover topics relevant t