When exposed to all wavelengths of light why might green sul

When exposed to all wavelengths of light, why might green sulfur bacteria be able to out-compete purple sulfur bacteria for their common substrate, sulfide?

Solution

Green sulfur bacteria oxidize sulfide and thiosulfate to sulfate, with extracellular globules of elemental sulfur as an intermediate. the genes are involved in the formation and consumption of these sulfur globules in the green sulfur bacterium Chlorobaculum tepidum. sulfur globule oxidation is strictly dependent on the dissimilatory sulfite reductase system, abolished sulfur globule oxidation and prevented formation of sulfate from sulfide, had no effect. The DSR system also seems to be involved in the formation of thiosulfate, because thiosulfate was released from wild-type cells during sulfide oxidation, but not from the dsr mutants. The dsr mutants incapable of complete substrate oxidation oxidized sulfide and thiosulfate about twice as fast as the wild-type, while having only slightly lower growth rate.. The increased oxidation rates seem to compensate for the incomplete substrate oxidation to satisfy the requirement for reducing equivalents during growth. A mutant in which two sulfide quinone oxidoreductases were deleted exhibited a decreased sulfide oxidation rate , yet formation and consumption of sulfur globules were not affected. The observation that mutants lacking the DSR system maintain efficient growth suggests that the DSR system is dispensable in environments with sufficiently high sulfide concentrations. Thus, the DSR system in GSB may have been acquired by horizontal gene transfer as a response to a need for enhanced substrate utilization in sulfide-limiting habitats.