Thiamine Sulfur Assimilation by Rhodopseudomonas palustris

Abstract

Thiamine is an essential vitamin for plant, mammal, and microbial metabolism, and can be found in many environments, including soil and wastewater. While thiamine biosynthesis has been widely studied, other biological uses of thiamine are unknown. As a complex molecule with three carbons, a nitrogen and a sulfur in its thiazoline ring structure, thiamine could provide carbon, nitrogen, or sulfur in nutrient-poor environments. In particular, in terrestrial soil which is very low in inorganic sulfur sources, I hypothesize that thiamine could be used by soil bacteria as a sulfur source. To test this hypothesis, the purple non-sulfur bacterium Rhodopseudomonas palustris, which lives in freshwater sediments, was grown with thiamine as a sole sulfur source. I found that R. palustris can use thiamine as a sulfur source. R. palustris has nitrogenase enzymes that help break C-S bonds and contribute to the breakdown of volatile organic sulfur compounds and sulfonates. To determine whether these genes might be involved in the thiamine sulfur assimilation pathway, mutants with nitrogenase genes deleted were created. We also carried out random barcoded transposon sequencing and heat mapping to assess which genes are required for assimilation of thiamine as sulfur source.