DISTRIBUTION OF SOIL HEAVY METALS ACROSS ECOLOGICALLY DISTINCT HABITATS ON SIGNY ISLAND, MARITIME ANTARCTICA AND ITS ASSOCIATION WITH BACTERIAL COMMUNITY COMPOSITION AND METABOLIC PROFILES

Abstract

Levels of heavy metals in Antarctic soils are generally low due to limited rates of pedogenesis and the relatively low influence of human activities. However, in recent decades, elevated metal concentrations have been detected both from natural sources and as a consequence of increasing levels of human activities in Antarctica. Tolerance towards heavy metal toxicity differs between members of the Antarctic soil microbial community. In this study, bacterial communities of five ecologically distinct locations on Signy Island (South Orkney Islands) were compared. These locations being Gourlay Peninsula, North Point, Pumphouse Lake, Jane Col and Berntsen Point. The diversity data obtained indicated four dominant phyla (Proteobacteria, Actinobacteria, Firmicutes and Bacteroidetes) in these soil ecosystems were positively correlated with soil edaphic factors (pH and water contents) and the availability of certain metals (magnesium, manganese and lead). Proteobacteria (50.5% to 79.6%), especially the genera Pseudomonas and Acinetobacter, were dominant in slightly acidic soils with relatively higher water contents accompanied by higher magnesium (Pumphouse Lake and the ornithogenically influenced Gourlay Peninsula and North Point), manganese (Pumphouse Lake and North Point) and lead concentration (Pumphouse Lake). High prevalence of Actinobacteria (47.0% to 78.4%), in particular the genus Arthrobacter, was detected in the more acidic and barren fellfield soils of Jane Col and Berntsen Point, along with higher manganese level (Jane Col). Elevated colonised of Firmicutes (8.30% to 21.6%), mainly the genus Enterococcus, at nutrient rich Gourlay Peninsula and North Point may due to influences of vertebrate activities. In general, metabolomic profile at the five sampling locations have detected metabolites are utilised as alternative carbon and energy sources, osmoprotectant and tolerant against acidic stress. Biosynthesis of metabolites that involved in encountered metal and oxidative stress are highly detected at Gourlay Peninsula, North Point and Pumphouse Lake. Locations characterised by high prevalence of Proteobacteria coincided with the detection of these metabolites. Isoleucine, leucine, aspartate, isobutyrate, formate tyrosine and phenylalanine are highly generated at Gourlay Peninsula. Isoleucine, leucine, isobuytrate, formate and aspartate can be utilised by microbes for either salinity, osmotic, acidic and metal tolerance in soil ecosystems, while tyrosine and phenylalanine are common microbial energy sources. High lysine, putrescine and glycine in North Point are also useful in regulating salinity, osmotic, acidic and metal homeostasis, while abundant lactate and sarcosine level in Pumphouse Lake are serves as carbon and energy sources. In Jane Col, the abundance of Actinobacteria among culturable bacterial isolates was consistent with the concentrations of cytosine, succinate, betaine, valine, dimethylamine and trehalose. These metabolites not only support growth of bacteria community as alternate carbon, energy and nitrogen sources, metabolites such as trehalose, valine and betaine are likewise act as desiccate and acidic protectants for microbes when under harsh conditions. Elevated xanthine and hypoxanthine in Berntsen Point reflected abundance of Actinobacteria as both metabolites are breakdown from guanine and inosine monophosphate (IMP) nucleotide, respectively; while 1,3-diaminopropane is a polyamine crucial in oxidative, acidic, salinity and osmotic resistant of microbes. In conclusion, our data indicate that microbial diversity and function in soil ecosystems on Signy Island are influenced by differences in heavy metal content and other edaphic factors.