Organic matter from Artic sea ice loss alters bacterial community structure and function

Continuing losses of multi-year sea ice (MYI) across the Arctic are resulting in first-year ice (FYI) dominating the Arctic ice pack. Melting FYI provides a strong seasonal pulse of dissolved organic matter (DOM) into surface waters; however, the biological impact of this DOM input is unknown. Here we show that DOM additions cause significant and contrasting changes in under-ice bacterioplankton abundance, production and species composition. Utilization of DOM was influenced by molecular size, with 10-100 kDa and >100 kDa DOM fractions promoting rapid growth of particular taxa, while uptake of sulfur and nitrogen-rich low molecular weight organic compounds shifted bacterial community composition. These results demonstrate the ecological impacts of DOM released from melting FYI, with wideranging consequences for the cycling of organic matter across regions of the Arctic Ocean transitioning from multi-year to seasonal sea ice as the climate continues to warm

Genetic signatures indicate widespread antibiotic resistance and phage infection in microbial communities of the McMurdo Dry Valleys, East Antarctica

The McMurdo Dry Valleys of Antarctica support extensive yet cryptic microbial communities but little evidence for ‘top-down’ herbivory control. A question therefore arises as to how standing microbial biomass is regulated. Here, we present results from a survey of soil and rock microbial community metagenomes using the GeoChip microarray that demonstrate antibiotic resistance and phage infection are widespread. We interrogated a range of dry valley locations from maritime to extreme inland sites. Antibiotic resistance genes were identified in three categories: beta-lactamases, tetracycline and vanomycin plus a range of transporter genes. Frequency of recovery generally reflected microbial diversity, with greatest abundance among Halobacteria, Proteobacteria and the photosynthetic bacteria (Chlorobi, Chloroflexi and Cyanobacteria). However, no clear differences between locations and soil/rock communities were apparent. Phage signals were also recovered from all locations in soil and rock communities. The Leviviridae, Myoviridae, Podoviridae and Siphoviridae were ubiquitous . The Corticoviridae occurred only in moisturesufficient hyporheic soils, the Microviridae occurred only in maritime and hyporheic sites and an unidentified group within the order Caudovirales occurred only at dry inland sites. We postulate that widespread antibiotic resistance indicates potential inter-specific interaction and that phage signals indicate possible ‘bottom-up’ trophic regulation in the dry valleys.http://link.springer.com/journal/3002016-02-28hb201