Generalist hydrocarbon-degrading bacterial communities in the oil-polluted water column of the North Sea.

The aim of this work was to determine the effect of light crude oil on bacterial communities during an experimental oil spill in the North Sea and in mesocosms (simulating a heavy, enclosed oil spill), and to isolate and characterize hydrocarbon-degrading bacteria from the water column. No oil-induced changes in bacterial community (3 m below the sea surface) were observed 32 h after the experimental spill at sea. In contrast, there was a decrease in the dominant SAR11 phylotype and an increase in Pseudoalteromonas spp. in the oiled mesocosms (investigated by 16S rRNA gene analysis using denaturing gradient gel electrophoresis), as a consequence of the longer incubation, closer proximity of the samples to oil, and the lack of replenishment with seawater. A total of 216 strains were isolated from hydrocarbon enrichment cultures, predominantly belonging to the genus Pseudoaltero monas; most strains grew on PAHs, branched and straight-chain alkanes, as well as many other carbon sources. No obligate hydrocarbonoclastic bacteria were isolated or detected, highlighting the potential importance of cosmopolitan marine generalists like Pseudoalteromonas spp. in degrading hydrocarbons in the water column beneath an oil slick, and revealing the susceptibility to oil pollution of SAR11, the most abundant bacterial clade in the surface ocean

SALT-LOVING MICROBES, LIMITS OF LIFE, MARS AND THE MESSINIAN SALINITY CRISIS

Hypersaline environments are subjected to dynamic environmental conditions which can result in precipitation of salt crystals, including halite. Microbial communities living in salt-saturated environments get trapped inside halite, including members of the three domains of life, but primarily haloarchaea. Entombment is a strategy for avoiding the harsh bittern brine that remains after halite precipitation. There is strong evidence that haloarchaea can survive in halite over geological time, which has remarkable implications about the limits of life and the possibility of life on Mars, where salt crystals are found. However, potential life on Mars would have to cope with high levels of solar and cosmic radiation. We asked whether co-entombment of Halobacterium spp. with the halophilic microalga. Dunaliella salina, enhances survival, e.g. by sharing nutrients. Surprisingly, D. salina did not enhance survival of Halobacterium spp., but its presence allowed D. salina to survive entombment for longer, at least over a short period of time. We also tested the capacity of Halobacterium spp. and the halophilic bacterial species Salinibacter ruber to tolerate UV and ionising radiation when in halite crystals. All species survived UV irradiation when in halite crystals and Halobacterium even survived a ionising radiation dose of 5 kGy. The longevity of haloarchaea, together with their tolerance to radiation, makes them a good model to investigate putative signs of past life in the Messinian, as well as past or present life on Mars, and potentially other celestial bodies

Impact of a simulated oil spill on benthic phototrophs and nitrogen-fixing bacteria in mudflat mesocosms

International audienceCoastal and estuarine ecosystems are highly susceptible to crude oil pollution. Therefore, in order to examine the resilience of benthic phototrophs that are pivotal to coastal ecosystem functioning, we simulated an oil spill in tidal mesocosms consisting of intact sediment cores from a mudflat at the mouth of the Colne Estuary, UK. At day 21, fluorescence imaging revealed a bloom of cyanobacteria on the surface of oiled sediment cores, and the upper 1.5cm thick sediment had 7.2 times more cyanobacterial and 1.7 times more diatom rRNA sequences when treated with oil. Photosystem II operating efficiency (Fq′/Fm′) was significantly reduced in oiled sediments at day 7, implying that the initial diatom-dominated community was negatively affected by oil, but this was no longer apparent by day 21. Oil addition significantly reduced numbers of the key deposit feeders, and the decreased grazing pressure is likely to be a major factor in the increased abundance of both diatoms and cyanobacteria. By day 5 concentrations of dissolved inorganic nitrogen were significantly lower in oiled mesocosms, likely resulting in the observed increase in nifH-containing, and therefore potentially dinitrogen-fixing, cyanobacteria. Thus, indirect effects of oil, rather than direct inhibition, are primarily responsible for altering the microphytobenthos. © 2012 Society for Applied Microbiology and Blackwell Publishing Ltd

The enigma of prokaryotic life in deep hypersaline anoxic basins

Deep hypersaline anoxic basins in the Mediterranean Sea are a legacy of dissolution of ancient subterranean salt deposits from the Miocene period. Our study revealed that these hypersaline basins are not biogeochemical dead ends, but support in situ sulfate reduction, methanogenesis, and heterotrophic activity. A wide diversity of prokaryotes was observed, including a new, abundant, deeply branching order within the Euryarchaeota. Furthermore, we demonstrated the presence of a unique, metabolically active microbial community in the Discovery basin, which is one of the most extreme terrestrial saline environments known, as it is almost saturated with MgCl2 (5 M)