Growth of Purple Sulfur Bacteria Allochromatium Vinosum on Solid Phase Metal Sulfides as Sulfur and Electron Sources
Purple sulfur bacteria (PSB) are photosynthetic microorganisms known for their vital roles in geochemical cycles, especially the sulfur cycle, within anoxic photic environments. PSB are also key contributors to the nitrogen, carbon, and oxygen cycles. This study focuses on the autotrophic growth of Allochromatium vinosum, a model strain of PSB, that utilize solid-phase metal sulfides (MS) as both sulfur and electron donors. Through characterizing the growth profiles of A. vinosum on pyrite (FeS2), nickel sulfide (NiS), and iron monosulfide (FeS) nanoparticles, respectively, and investigating the bacteria-MS interaction mechanisms, this work expands our current knowledge of the metabolic capabilities and flexibility of Allochromatium vinosum, provides new insight into the mechanisms of bacterial-nanoparticles interactions, and further, possibly opens new research avenues in bacterial extracellular electron transfer and artificial photosynthesis. In this study, growth profiles findings coupled with transcriptome analysis showed that A. vinosum could use pyrite and NiS for autotrophic growth, while conflicting findings were found for FeS. Optical density plots of biotic pyrite and NiS showed twice the growth compared to the negative control. IC, ICP-MS, XPS and HR-TEM served as complementary findings providing supporting evidence, along with sulfur oxidation gene profiles, of the transformations experienced by MS results of exposure to A. vinosum, as well as providing evidence of an active sulfur oxidation pathway. In the case of FeS, OD did not go beyond growth displayed by the negative control implying that growth in FeS might not go beyond the effects supporting the growth in the negative control. Nonetheless, evidence points to active sulfur oxidation pathway in this metal system through XPS increase of the polysulfide portions compared to the abiotic control, as well as the increase in sulfate concentration to ~400uM on IC. Furthermore, all systems displayed a severe downregulation of photosynthetic genes puf and puc but comparable expression values for carotenoid genes to the positive control. Finally, all MS systems displayed a collection of redox active cytochromes and hydrogenases, some of which were associated with the membrane (LXXC), redox activity (CXXCH) and others with secretory pathway (signal peptide). Other genes such as transporters genes, pili and hypothetical proteins were used to generate a more complete assessment of the utilization of MS by A. vinosum, as well collection of evidence which proteins are potentially involved in the unidentified electron transfer pathway that allows for utilization of NiS and pyrite, while more studies need to be carried to assess the FeS system.
Alarcon, Hugo, "Growth of Purple Sulfur Bacteria Allochromatium Vinosum on Solid Phase Metal Sulfides as Sulfur and Electron Sources" (2023). ETD Collection for University of Texas, El Paso. AAI30636451.