Deep-Sea Biofilms, Historic Shipwreck Preservation and the Deepwater Horizon Spill

Bacterial biofilms at times undergo regulated and coordinated dispersal events where sessile biofilm cells convert to free-swimming, planktonic bacteria. In the opportunistic pathogen Pseudomonas aeruginosa, we previously observed that dispersal occurs concurrently with three interrelated processes within mature biofilms: (i) production of oxidative or nitrosative stress-inducing molecules inside biofilm structures, (ii) bacteriophage induction, and (iii) cell lysis. Here we examine whether specific reactive oxygen or nitrogen intermediates play a role in cell dispersal from P. aeruginosa biofilms. We demonstrate the involvement of anaerobic respiration processes in P. aeruginosa biofilm dispersal and show that nitric oxide (NO), used widely as a signaling molecule in biological systems, causes dispersal of P. aeruginosa biofilm bacteria. Dispersal was induced with low, sublethal concentrations (25 to 500 nM) of the NO donor sodium nitroprusside (SNP). Moreover, a P. aeruginosa mutant lacking the only enzyme capable of generating metabolic NO through anaerobic respiration (nitrite reductase, DeltanirS) did not disperse, whereas a NO reductase mutant (DeltanorCB) exhibited greatly enhanced dispersal. Strategies to induce biofilm dispersal are of interest due to their potential to prevent biofilms and biofilm-related infections. We observed that exposure to SNP (500 nM) greatly enhanced the efficacy of antimicrobial compounds (tobramycin, hydrogen peroxide, and sodium dodecyl sulfate) in the removal of established P. aeruginosa biofilms from a glass surface. Combined exposure to both NO and antimicrobial agents may therefore offer a novel strategy to control preestablished, persistent P. aeruginosa biofilms and biofilm-related infections.

Increasing global temperatures are having a profound impact in the Arctic, including the dramatic loss of multiyear sea ice in 2007 that has continued to the present. The majority of life in the Arctic is microbial and the consequences of climate-mediated changes on microbial marine food webs, which are responsible for biogeochemical cycling and support higher trophic levels, are unknown. We examined microbial communities over time by using high-throughput sequencing of microbial DNA collected between 2003 and 2010 from the subsurface chlorophyll maximum (SCM) layer of the Beaufort Sea (Canadian Arctic). We found that overall this layer has freshened and concentrations of nitrate, the limiting nutrient for photosynthetic production in Arctic seas, have decreased. We compared microbial communities from before and after the record September 2007 sea ice minimum and detected significant differences in communities from all three domains of life. In particular, there were significant changes in species composition of Eukarya, with ciliates becoming more common and heterotrophic marine stramenopiles (MASTs) accounting for a smaller proportion of sequences retrieved after 2007. Within the Archaea, Marine Group I Thaumarchaeota, which earlier represented up to 60% of the Archaea sequences in this layer, have declined to <10%. Bacterial communities overall were less diverse after 2007, with a significant decrease of the Bacteroidetes. These significant shifts suggest that the microbial food webs are sensitive to physical oceanographic changes such as those occurring in the Canadian Arctic over the past decade.