# Reporting Key Features in Cold-Adapted Bacteria
## 5 Functional Attributes of Cold-Adapted Bacterial Communities  
In the next section, several cold bacterial community studies using global metagenome, metatranscriptome and metaproteome approaches are analyzed. The overall available information of these communities shows the constancy in general functional attributes involved in cold adaptation and the relevance of other metabolisms and features present in the complex microbial communities. Metagenome analysis of cyanobacterial mats from Arctic and Antarctic ice shelves showed that genes coding for functional responses to environmental stress such as exopolysaccharides, cold shock proteins and membrane modifications were found in all analyzed metagenomes [66]. The finding of a higher abundance of sequences (reads) matching the sigma B genes in the Antarctic mat was proposed as a feature reflecting more severe osmotic stress during freeze-up of the Antarctic ponds [66]. The results of six metagenomic datasets from different microbial mat communities of the perennially ice-covered Antarctic Lake Joyce were used to filter cold adaptation protein information, including antifreeze proteins, cold-shock DEAD-box protein A, cold-shock family of proteins (CSPs; including CspA, CspB, CspC, CspD, CspE and CspG), fatty acid desaturase, ice nucleation protein and trehalose synthase [67]. The analysis showed that while the cold-shock family of proteins, cold-shock DEAD-box protein A, antifreeze proteins, fatty acid desaturase and trehalose synthase were present in all mat samples at different levels, the ice nucleation protein was only found at very low levels in some of the samples [67], probably reflecting the presence of generalized and particular mechanisms for cold adaptation in the bacterial communities. Interestingly, a metagenomic study of the biofilm and planktonic microbial communities of an acid mine drainage stream located below ground at a low-temperature (6-10 \({}^{\circ}\)C) in Kristineberg mine (Sweden) also showed functional characteristics previously reported as related to cold growth. These functional characteristics include cold-shock and anti-freeze proteins and several compatible solutes production pathways, besides the typical functions related to pH homeostasis and metal resistance expected to thrive in this acidic metal-containing ecosystem [68]. A recent metagenomic work analyzed the bacterial communities of Alaskan Pleistocene permafrost over geologic time by exploring a chronosequence from 19,000 to 33,000 years before the present day [69]. The results showed shifts consistent with long-term survival strategies involving scavenging detrital biomass, horizontal gene transfer, chemotaxis, dormancy, environmental sensing and stress response, thus associating the increase of abundance of many genes with age with microbial community adaptation to extreme cryogenic environment [69]. A comparative metaproteomic study of winter and summer bacterioplankton from Antarctic Peninsula coastal surface waters showed differences in each season [70]. While in the summer, autotrophic carbon assimilation appears to be driven by oxygenic photoautotrophy, consistent with high light availability and intensity, during the dark winter chemolithautotrophic metabolism involving the 3-hydroxypropionate/4-hydroxybutyrate cycle and the reverse tricarboxylic acid cycle represented the main processes [70]. Metatranscriptome analysis of microbial communities in Alaskan permafrost soils showed the dominance of stress responses, survival strategies and maintenance processes under frozen conditions, while upon thawing, a rapid enzymatic response to decomposing soil organic matter was observed as well as transcripts related to acetogenesis and heterotrophic methanogenic pathways utilizing acetate, methanol and methylamine [71]. The understanding of microbial communities is complex, because many metabolic groups coexist in the environment and much remains to be discovered.