The Content of Polyarenes in Soils of Antarctica: Variability across Landscapes

Soil cover of the Earth is faced with intensive polychemical contamination. The pathways of the key pollutants are not investigated enough. Thus, the occasional transportation of soils to remote regions could serve as an informative tool for the elaboration of threshold levels of hazardous materials concentration. One of the most striking examples of such transboundary impact was the transfer of soils and grounds to the Antarctic stations Russkaya and Leningradskaya (before the implementation of the Madrid Protocol in 1991). Thus, the complex investigation of qualitative and quantitative composition of polycyclic aromatic hydrocarbons (PAHs) in soils of various genesis (transported from Eurasia and pristine) of Antarctic have been conducted by the method of high-performance liquid chromatography (HPLC) in a gradient elution mode. The variability of PAHs content was evaluated across landscapes: pristine (the Hudson Mountains and the Haswell Archipelago), contaminated soils (stations Myrniy, Druzhnaya 4 and Bellinshausen) and unique samples of former agrosoils transported by fly in-fly of polar staff from St. Petersburg to Antarctic for local polar greenhouses in the Soviet times, when it was not strictly prohibited. The selected objects of study allow us to not only estimate the degree of contamination of Antarctic soils and grounds, but to also make it possible to assess the rate of PAH degradation in Antarctic conditions. Both high molecular and low molecular PAHs are accumulated following intense anthropogenic activity (fossil organic fuel combustion). The PAHs pool is dominated by low molecular weight representatives (naphthalene, phenanthrene, fluoranthene, pyrene). In most cases, the highest concentrations of benz(a)pyrene does not exceed the Russian Threshold Standard rate, which is the strictest one in the world. The statistical analysis of raw data allowed us to conclude that the contamination of pristine soils of Antarctica across variable landscapes is at the very initial stage. However, we recorded extremely high levels of PAHs in the transported former agrosoils. We can assume that our data could be used as background levels for the elaboration of threshold concentrations of the PAHs for such an internationally managed region as Antarctica.

Manganese-Oxidizing Antarctic Bacteria (Mn-Oxb) Release Reactive Oxygen Species (ROS) as Secondary Mn(II) Oxidation Mechanisms to Avoid Toxicity

Manganese (Mn) oxidation is performed through oxidative Mn-oxidizing bacteria (MnOxb) as the main bio-weathering mechanism for Mn(III/IV) deposits during soil formation. However, with an increase in temperature, the respiration rate also increases, producing Reactive Oxygen Species (ROS) as by-products, which are harmful to microbial cells. We hypothesize that bacterial ROS oxidize Mn(II) to Mn(III/IV) as a secondary non-enzymatic temperature-dependent mechanism for cell protection. Fourteen MnOxb were isolated from Antarctic soils under the global warming effect, and peroxidase (PO) activity, ROS, and Mn(III/IV) production were evaluated for 120 h of incubation at 4 °C, 15 °C, and 30 °C. ROS contributions to Mn oxidation were evaluated in Arthrobacter oxydans under antioxidant (Trolox) and ROS-stimulated (menadione) conditions. The Mn(III/IV) concentration increased with temperature and positively correlated with ROS production. ROS scavenging with Trolox depleted the Mn oxidation, and ROS-stimulant increased the Mn precipitation in A. oxydans. Increasing the Mn(II) concentration caused a reduction in the membrane potential and bacterial viability, which resulted in Mn precipitation on the bacteria surface. In conclusion, bacterial ROS production serves as a complementary non-enzymatic temperature-dependent mechanism for Mn(II) oxidation as a response in warming environments.

The Abundance and Taxonomic Diversity of Filterable Forms of Bacteria during Succession in the Soils of Antarctica (Bunger Hills)

Previous studies have shown that a significant part of the bacterial communities of Antarctic soils is represented by cells passing through filters with pore sizes of 0.2 µm. These results raised new research questions about the composition and diversity of the filterable forms of bacteria (FFB) in Antarctic soils and their role in the adaptation of bacteria to the extreme living conditions. To answer such questions, we analyzed the succession of bacterial communities during incubation of Antarctic soil samples from the Bunger Hills at increased humidity and positive temperatures (5°C and 20°C). We determined the total number of viable cells by fluorescence microscopy in all samples and assessed the taxonomic diversity of bacteria by next-generation sequencing of the 16S rRNA gene region. Our results have shown that at those checkpoints where the total number of cells reached the maximum, the FFB fraction reached its minimum, and vice versa. We did not observe significant changes in taxonomic diversity in the soil bacterial communities during succession. During our study, we found that the soil bacterial communities as a whole and the FFB fraction consist of almost the same phylogenetic groups. We suppose rapid transition of the cells of the active part of the bacterial population to small dormant forms is one of the survival strategies in extreme conditions and contributes to the stable functioning of microbial communities in Antarctic soils.

In Situ Rhizosphere Microbiome in Antarctic Vascular Plants, Modulated by Soil Condition

ABSTRACT Antarctic soils are considered young soils; therefore, the microbiota associated with Antarctic vascular plants play a critical role in their productivity. In this research, we compared the microbiota from three different soil conditions using a 16S rRNA and internal transcribed spacer rRNA gene amplicon approach for bacterial and fungal communities.

Experimental warming of bryophytes increases the population density of the nematode Plectus belgicae in maritime Antarctica

Despite nematodes routinely being the most frequent soil- and bryophyte-associated animals in maritime Antarctica, there is a lack of clarity about the influence of warming on their populations in the region. Here, we report the results of a field experiment on Adelaide Island that tested the effects of warming with open-top chambers (OTCs) for 37 months on nematodes associated with the bryophytes Cephaloziella varians and Sanionia uncinata. Over the experiment's duration, OTCs increased the population density of the nematode Plectus belgicae in mats of both bryophytes by six-fold, with four- to seven-fold increases in the abundances of male, female and juvenile P. belgicae in warmed mats, and with the largest effects on the abundances of juveniles. Despite C. varians, which is black in colour, warming to a greater extent than S. uncinata during summer, no interactive effects of OTCs and bryophyte species were recorded on the population density of P. belgicae. Our results corroborate a previous study showing that warming increases Plectus population densities in maritime Antarctic soils, with implications for the region's terrestrial food webs.