Iron Demand by Thermophilic and Mesophilic Bacteria Isolated from an Antarctic Geothermal Soil

Antarctic Geothermal Soils Exhibit an Absence of Regional Habitat Generalist Microorganisms

Active geothermal systems are relatively rare in Antarctica and represent metaphorical islands ideal to study microbial dispersal. In this study, we tested the macro-ecological concept that high dispersal rates result in communities being dominated by either habitat generalists or specialists by investigating the microbial communities on four geographically separated geothermal sites on three Antarctic volcanoes (Mts. Erebus, Melbourne, and Rittman). We found that the microbial communities at higher temperature (max 65°C) sites (Tramway Ridge on Erebus and Rittmann) were unique from each other and were dominated by a variety of novel Archaea from class Nitrososphaeria, while lower temperature (max 50°C) sites (Western Crater on Erebus and Melbourne) had characteristically mesophilic communities (Planctomycetes, Acidobacteriota, etc.) that were highly similar. We found that 97% of the detected microbial taxa were regional habitat specialists, with no generalists, with community assembly driven by high dispersal rates and drift (25% and 30% of community assembly, respectively), not environmental selection. Our results indicate that for microbial communities experiencing high dispersal rates between isolated communities, habitat specialists may tend to out-compete habitat generalists.

Microbial Communities Present in Hydrothermal Sediments from Deception Island, Antarctica

Deception Island is a geothermal location in Antarctica that presents active fumaroles, which confers unique characteristics to this habitat. Several studies about microbial communities in Antarctica have been carried out, nevertheless, Antarctic microbiota is still partially unknown. Here we present a multidisciplinary study about sediments obtained by deposition during 4 years in which several approaches have been considered for their characterization. First, a physicochemical characterization, using ionic chromatography and mass spectrometry for the determination of most abundant ions (chloride and sulphate) and elements (mainly silicon), was conducted. In addition, the total microbial community was studied using a metataxonomical approach, revealing a bacterial community dominated by Proteobacteria and Thaumarchaeota as the main archaeal genera and a fungal community mainly composed by Aspergillaceae. Culture-dependent studies showed low microbial diversity, only achieving the isolation of Bacillus-related species, some of them thermophilic, and the isolation of common fungi of Aspergillus or Penicillium spp. Furthermore, diatoms were detected in the sediment and characterized attending to their morphological characteristics using scanning electron microscopy. The study reveals a high influence of the physicochemical conditions in the microbial populations and their distribution, offering valuable data on the interaction between the island and water microbiota.

Paenibacillus macquariensis subsp. defensor subsp. nov., isolated from boreal soil

Two Gram-variable, aerobic, motile, rod-shaped, endospore-forming bacterial strains, M4-2T and M4-1, were isolated from soil samples collected from Oblast Magadan, Russian Far East, as micro-organisms antagonistic to the psychrophilic phytopathogenic fungus Typhula ishikariensis. Strains M4-2T and M4-1 were identified as members of the genus Paenibacillus by phenotypic and phylogenetic analyses based on 16S rRNA gene sequences. The strains contained anteiso-C15:0 as the major fatty acid (63.0-64.7%) and MK-7 as the major isoprenoid quinone. The DNA G+C contents were 42.8 and 41.7 mol%, respectively. 16S rRNA gene sequence analysis showed that strains M4-2T and M4-1 exhibited high similarities with Paenibacillus macquariensis DSM 2T (99.5 and 99.7%, respectively) and Paenibacillus antarcticus LMG 22078T (99.4 and 99.5%, respectively). There were no clear differences in the phenotypic characteristics and chemotaxonomic and phylogenetic data between the novel isolates and P. macquariensis DSM 2T. DNA-DNA hybridization experiments between strain M4-2T and P. macquariensis DSM 2T and P. antarcticus LMG 22078T revealed reassociation values of 56 and 49%, respectively. Multilocus sequence analysis confirmed the differences between the new isolates and reference strains that were observed with the DNA-DNA hybridization studies. On the basis of the results described above, it is proposed that the isolates represent a novel subspecies of P. macquariensis, Paenibacillus macquariensis subsp. defensor subsp. nov. The type strain is M4-2T (=JCM 14954T=NCIMB 14397T).

Microbial biodiversity of thermophilic communities in hot mineral soils of Tramway Ridge, Mount Erebus, Antarctica

Tramway Ridge, located near the summit of Mount Erebus in Antarctica, is probably the most remote geothermal soil habitat on Earth. Steam fumaroles maintain moist, hot soil environments creating extreme local physicochemical differentials. In this study a culture-independent approach combining automated rRNA intergenic spacer analysis (ARISA) and a 16S rRNA gene library was used to characterize soil microbial (Bacterial and Archaeal) diversity along intense physicochemical gradients. Statistical analysis of ARISA data showed a clear delineation between bacterial community structure at sites close to fumaroles and all other sites. Temperature and pH were identified as the primary drivers of this demarcation. A clone library constructed from a high-temperature site led to the identification of 18 novel bacterial operational taxonomic units (OTUs). All 16S rRNA gene sequences were deep branching and distantly (85-93%) related to other environmental clones. Five of the signatures branched with an unknown group between candidate division OP10 and Chloroflexi. Within this clade, sequence similarity was low, suggesting it contains several yet-to-be described bacterial groups. Five archaeal OTUs were obtained and exhibited high levels of sequence similarity (95-97%) with Crenarchaeota sourced from deep-subsurface environments on two distant continents. The novel bacterial assemblage coupled with the unique archaeal affinities reinvigorates the hypotheses that Tramway Ridge organisms are relics of archaic microbial lineages specifically adapted to survive in this harsh environment and that this site may provide a portal to the deep-subsurface biosphere.