An investigation of the starvation survival response in the sulphate-reducing bacteria
Presented results suggest that Desulfovibrio salexigens decreased in size in response to starvation. This size decrease was measured using a laser particle sizer which proved to be sufficiently sensitive for this purpose. Reduction in cell size occurred much quicker and to a greater extent when trace metals were removed from the starvation media. The survival of this organism also appeared to depend on the starvation media used with cells retaining 100% viability when starved in the absence of trace metals. Viability rapidly decreased when starved in the presence of trace metals. Of the starving cell suspension which retained 100% viability, only a small percentage of the cells were of a size that could constitute an ultramicrobacterial form. This result suggests the need to redefine the size limits and the actual definition of ultramicrobacteria. When in a survival state, Desulfovibrio salexigens demonstrated an enhanced survival to elevated temperatures although the actual percentage of cells surviving was very small. Although attachment to surfaces has been proposed as a survival strategy in many marine organisms, starved D. salexigens did not demonstrate this phenomenon. The passage of these organisms through sandstone cores resulted in an increased porosity but decreased permeability in all cases but this was thought to be due to the presence of clays in the sample rather than the plugging effects of the bacteria.