Magnetotactic Bacteria in Microcosms Originating from the French Mediterranean Coast Subjected to Oil Industry Activities

Abstract

Magnetotactic bacteria (MTB) mineralize nanosized magnetite or greigite crystals within cells and thus play an important role in the biogeochemical process. Despite decades of research, knowledge of MTB distribution and ecology, notably in areas subjected to oil industry activities, is still limited. In the present study, we investigated the presence of MTB in the Gulf of Fos, French Mediterranean coast, which is subjected to intensive oil industry activities. Microcosms containing sediments/water (1:2, v/v) from several sampling sites were monitored over several weeks. The presence of MTB was revealed in five of eight sites. Diverse and numerous MTB were revealed particularly from one site (named CAR), whilst temporal variations of a homogenous magnetotactic cocci population was shown within the LAV site microcosm over a 4-month period. Phylogenetic analysis revealed that they belonged to Alphaproteobacteria, and a novel genus from the LAV site was evidenced. Among the physicochemical parameters measured, a correlation was shown between the variation of MTB abundance in microcosms and the redox state of sulphur compounds.

Constant Flux of Spatial Niche Partitioning through High-Resolution Sampling of Magnetotactic Bacteria

“…Other workers found that salinity, nitrate concentrations, and sulfate concentrations correlate with the amounts of MTB (16,19,26,33). We observed worms and small aquatic plants living in the sediment.…”

“…2). Initially, MTB rods and MTB spirilla predominated, but MTB cocci became the dominant group after day 37, which has been found in natural habitats (16,19,26,27). Moreover, when MTB cocci had similar spatial distributions between adjacent days of counting, MTB spirilla were concentrated in different places between those same adjacent days of counting and vice versa.…”

“…As they contain 2 to 4% (dry weight) Fe (15,16), MTB could influence iron cycles in nature by acting to sequester Fe in sediments (17). Several studies have addressed the spatiotemporal variation of MTB along vertical profiles (16,18,19), yet much less is known about how their horizontal distribution varies in space and time. Specifically, we question how well MTB populations measured in a given place (a spatial niche) represent a particular environment through time; e.g., do the populations remain fixed in a limited area, move randomly from place to place, or some combination of the two, and over what time scales?…”

Ecology, Diversity, and Evolution of Magnetotactic Bacteria

“…Moreover, within the OAI itself, different species of MTB occupy different positions that represent different specific chemical conditions at that depth. Biogeographic studies indicate that some environmental parameters such as salinity, temperature, nitrate, or sulfur compounds could explain MTB abundance or community differences (17)(18)(19)(20)(21). One study reported that despite the fact that the largest proportion of MTB appears to be detected within the suboxic zone, a strict correlation between the distribution of MTB and individual geochemical parameters has never been shown (22).…”

“…Although this may not seem significant, there are relative few groups or investigators studying the diversity of MTB, although this number is now increasing. As stated above, the diversity of MTB has been studied mainly in several locations in North America (2, 26-28, 31, 32, 44, 53, 75, 171), Brazil (19, 42, 86, 148, 166), China (17-21, 31-33), Germany (22, 34, 45, 93, 94, 96, 145, 150), and France (21,49,89). Clearly, then, little is known regarding MTB of the Southern Hemisphere.…”