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Polar regions contain a wide variety of lentic ecosystems. These include periodic ponds that have a significant impact on carbon and nitrogen cycling in polar environments. This study was conducted to assess the taxonomic and metabolic diversity of bacteria found in Antarctic pond affected by penguins and sea elephants and to define their role in ongoing processes. Metabolic assays showed that of the 168 tested heterotrophic bacteria present in the Antarctic periodic pond, 96% are able to degrade lipids, 30% cellulose, 26% proteins, and 26% starch. The taxonomic classification of the obtained isolates differs from that based on the composition of the 16S rRNA relative abundances in the studied pond. The dominant Actinobacteria constituting 45% of isolates represents a low proportion of the community, around 4%. With the addition of run-off, the proportions of inhabiting bacteria changed, including a significant decrease in the abundance of Cyanobacteria , from 2.38 to 0.33%, increase of Firmicutes from 9.32 to 19.18%, and a decreasing richness (Chao1 index from 1299 to 889) and diversity (Shannon index from 4.73 to 4.20). Comparative studies of communities found in different Antarctic environments indicate a great role for penguins in shaping bacterial populations. [ABSTRACT FROM AUTHOR]

Cold-active bacteria of the genus Polaromonas (class Betaproteobacteria) are important components of glacial microbiomes. In this study, extrachromosomal replicons of 26 psychrotolerant Polaromonas strains, isolated from Arctic and Antarctic glaciers, were identified, sequenced, and characterized. The plasmidome of these strains consists of 13 replicons, ranging in size from 3,378 to 101,077 bp. In silico sequence analyses identified the conserved backbones of these plasmids, composed of genes required for plasmid replication, stable maintenance, and conjugal transfer. Host range analysis revealed that all of the identified plasmids are narrow-host-range replicons, only able to replicate in bacteria of closely related genera (Polaromonas and Variovorax) of the Comamonadaceae family. Special attention was paid to the identification of plasmid auxiliary genetic information, which may contribute to the adaptation of bacteria to environmental conditions occurring in glaciers. Detailed analysis revealed the presence of genes encoding proteins potentially involved in (i) protection against reactive oxygen species, ultraviolet radiation, and low temperatures; (ii) transport and metabolism of organic compounds; (iii) transport of metal ions; and (iv) resistance to heavy metals. Some of the plasmids also carry genes required for the molecular assembly of iron–sulfur [Fe-S] clusters. Functional analysis of the predicted heavy metal resistance determinants demonstrated that their activity varies, depending on the host strain. This study provides the first molecular insight into the mobile DNA of Polaromonas spp. inhabiting polar glaciers. It has generated valuable data on the structure and properties of a pool of plasmids and highlighted their role in the biology of psychrotolerant Polaromonas strains and their adaptation to the environmental conditions of Arctic and Antarctic glaciers. [ABSTRACT FROM AUTHOR]

Highlights: [•] Antarctic, strictly psychrophilic Pseudomonas sp. GLE121 carries three plasmids. [•] Plasmids pGLE121P1 and pGLE121P2 represent the IncP-9 and IncP-7 groups, respectively. [•] Plasmid pGLE121P3 carries a predicted conjugal transfer system. [•] Plasmid pGLE121P3 carries a rulAB operon, possibly responsible for UV tolerance. [•] The plasmids may participate in horizontal gene transfer in the Antarctic environment. [Copyright &y& Elsevier]

Antarctic regions are characterized by low temperatures and strong UV radiation. This harsh environment is inhabited by psychrophilic and psychrotolerant organisms, which have developed several adaptive features. In this study, we analyzed two Antarctic bacterial strains, Planococcus sp. ANT_H30 and Rhodococcus sp. ANT_H53B. The physiological analysis of these strains revealed their potential to produce various biotechnologically valuable secondary metabolites, including surfactants, siderophores, and orange pigments. The genomic characterization of ANT_H30 and ANT_H53B allowed the identification of genes responsible for the production of carotenoids and the in silico reconstruction of the pigment biosynthesis pathways. The complex manual annotation of the bacterial genomes revealed the metabolic potential to degrade a wide variety of compounds, including xenobiotics and waste materials. Carotenoids produced by these bacteria were analyzed chromatographically, and we proved their activity as scavengers of free radicals. The quantity of crude carotenoid extracts produced at two temperatures using various media was also determined. This was a step toward the optimization of carotenoid production by Antarctic bacteria on a larger scale. [ABSTRACT FROM AUTHOR]

Pseudomonas spp. are widely distributed in various environments around the world. They are also common in the Antarctic regions. To date, almost 200 plasmids of Pseudomonas spp. have been sequenced, but only 12 of them were isolated from psychrotolerant strains. In this study, 15 novel plasmids of cold-active Pseudomonas spp. originating from the King George Island (Antarctica) were characterized using a combined, structural and functional approach, including thorough genomic analyses, functional analyses of selected genetic modules, and identification of active transposable elements localized within the plasmids and comparative genomics. The analyses performed in this study increased the understanding of the horizontal transfer of plasmids found within Pseudomonas populations inhabiting Antarctic soils. It was shown that the majority of the studied plasmids are narrow-host-range replicons, whose transfer across taxonomic boundaries may be limited. Moreover, structural and functional analyses enabled identification and characterization of various accessory genetic modules, including genes encoding major pilin protein (PilA), that enhance biofilm formation, as well as active transposable elements. Furthermore, comparative genomic analyses revealed that the studied plasmids of Antarctic Pseudomonas spp. are unique, as they are highly dissimilar to the other known plasmids of Pseudomonas spp. [ABSTRACT FROM AUTHOR]

The knowledge on plasmids of cold-active bacteria is highly limited. In this study, the molecular characterization of the pA3J1 plasmid of Antarctic psychrotolerant bacterium Pseudomonas sp. ANT_J3 was performed. Within this plasmid, thirteen putative open reading frames were identified. Nine of them encoded proteins involved in replication, partitioning, postsegregational elimination of plasmid-less cells (via a toxin-antitoxin system activity), multimer resolution and mobilization by conjugal transfer. These genes constitute the plasmid backbone. The functional analysis of the pA3J1 maintenance region revealed that it is a narrow host range replicon, stably maintained in the host cells by the combined activities of the partitioning and relBE -type toxin-antitoxin systems. It was also suggested that the replication system of the pA3J1 plasmid may be temperature-sensitive. Comparative analyses revealed the presence of 16 Pseudomonas plasmids encoding homologous replication proteins and 5 plasmids carrying mobA genes homologous to the corresponding gene of pA3J1. The relaxase (MobA) of the pA3J1 plasmid was classified into MOB Q family, and the phylogenetic analysis suggested that this may be a representative of a novel group (or subgroup) within this family. The structural and comparative analyses revealed that the arrangement of genetic modules in the pA3J1 plasmid is unique. [ABSTRACT FROM AUTHOR]