Psychrophilic microorganisms: challenges for life

Abstract

The ability of psychrophiles to survive and proliferate at low temperatures implies that they have overcome key barriers inherent to permanently cold environments. These challenges include: reduced enzyme activity; decreased membrane fluidity; altered transport of nutrients and waste products; decreased rates of transcription, translation and cell division; protein cold-denaturation; inappropriate protein folding; and intracellular ice formation. Cold-adapted organisms have successfully evolved features, genotypic and/or phenotypic, to surmount the negative effects of low temperatures and to enable growth in these extreme environments. In this review, we discuss the current knowledge of these adaptations as gained from extensive biochemical and biophysical studies and also from genomics and proteomics.

Adaptation of model proteins from cold to hot environments involves continuous and small adjustments of average parameters related to amino acid composition

“…This leads to a decreased thermostability, but improves the catalytic rate of the cold-adapted enzymes at 'normal' temperatures, with respect to mesophiles. Usually, psychrophilic enzymes possess a sufficiently high catalysis at their optimum growth temperatures, even though their thermophilicities improve far beyond in some cases (D'Amico et al, 2006). Moreover, psychrophilic proteins have a slightly lower "density" compared to mesophilic ones, as revealed through gel-filtration experiments.…”

“…Cold and hot temperatures are hostile habitats for life, and organisms having an optimum growth under the most extreme temperature conditions are named psychrophiles and hyperthermophiles, respectively. Properties of these microorganisms belonging to eubacterial or archaeal kingdom have been extensively reviewed (Stetter, 1996;Stetter, 1998;Stetter, 1999;Huber et al, 2000;Deming, 2002;D'Amico et al, 2006;Cavicchioli, 2006). Indeed, it is known that some psychrophiles sustain a residual biological activity even at -20°C (Deming, 2002), whereas some hyperthermophiles are able to grow up to 113°C (Blöchl et al, 1997).…”

“…However, hyperthermophilic proteins are endowed with an extraordinary heat stability, as a consequence of a more tight compactness of the protein structure (Vieille and Zeikus, 2001). Vice versa, the psychrophilic counterparts possess an increased protein flexibility, which in most cases leads to a decreased stability compared to mesophilic proteins (D'Amico et al, 2006); in some psychrophilic enzymes the protein flexibility is enhanced in localized regions of the protein structure (Fields and Somero, 1998). Temperature adaptation of proteins is mostly relevant for the catalytic properties of the enzymes, as they must adapt the rate of the catalyzed reaction to the growth temperature of the organism.…”

“…The frequencies of each amino acid residue have been derived from an average amino acid composition, in order to discover a possible bias in the amino acid usage of the considered extremophile. However, each microbial source and each protein seems to adopt only a few of possible, and even counteracting, structural trends (D'Amico et al, 2006;Sterner and Liebl, 2001). For instance, the amino acid bias discovered in some 7 psychrophiles (Sanders et al, 2003) is not applicable to similarly adapted, but evolutionary distant sources (Rabus et al, 2004;Medigue et al, 2005).…”

A Unique Capsular Polysaccharide Structure from the Psychrophilic Marine Bacterium Colwellia psychrerythraea 34H That Mimics Antifreeze (Glyco)proteins

“…Besides a general interest in understanding mechanisms underlying their ability to survive and grow at temperatures near or below the freezing point of water, in recent years cold-adapted microorganisms have received extra consideration due to the potential biotechnological applications of their enzymes. [1][2][3] Because microorganisms are at thermal equilibrium with their environment, it is reasonable to assume that structural and functional components in psychrophiles (optimal growth at ≤ 15°C) have adapted, to some degree, to the requirements of a low temperature existence, 4 including the possible presence of ice crystals in their immediate surroundings. The reported mechanisms of bacterial adaptation to low temperature include the over-expression of cold-shock and heat-shock proteins, the presence of unsaturated and branched fatty acids that maintain membrane fluidity, 5 the different phosphorylation of membrane proteins and lipopolysaccharides, [6][7][8][9][10][11] and the production of cold-active enzymes, 12 antifreeze proteins and cryoprotectants.…”