Sulfate Transporters in Dissimilatory Sulfate Reducing Microorganisms: A Comparative Genomics Analysis.

Angeliki Marietou,Kasper U Kjeldsen,Bo B Jørgensen,Hans Røy

doi:10.3389/fmicb.2018.00309

Abstract

The first step in the sulfate reduction pathway is the transport of sulfate across the cell membrane. This uptake has a major effect on sulfate reduction rates. Much of the information available on sulfate transport was obtained by studies on assimilatory sulfate reduction, where sulfate transporters were identified among several types of protein families. Despite our growing knowledge on the physiology of dissimilatory sulfate-reducing microorganisms (SRM) there are no studies identifying the proteins involved in sulfate uptake in members of this ecologically important group of anaerobes. We surveyed the complete genomes of 44 sulfate-reducing bacteria and archaea across six phyla and identified putative sulfate transporter encoding genes from four out of the five surveyed protein families based on homology. We did not find evidence that ABC-type transporters (SulT) are involved in the uptake of sulfate in SRM. We speculate that members of the CysP sulfate transporters could play a key role in the uptake of sulfate in thermophilic SRM. Putative CysZ-type sulfate transporters were present in all genomes examined suggesting that this overlooked group of sulfate transporters might play a role in sulfate transport in dissimilatory sulfate reducers alongside SulP. Our in silico analysis highlights several targets for further molecular studies in order to understand this key step in the metabolism of SRMs.

Highlights

Dissimilatory sulfate reduction is a key metabolic process in anoxic environments
Even though dissimilatory sulfate reduction is a key process in anoxic environments ranging from the deep subseafloor to the human digestive tract, there are still significant gaps in our knowledge of the steps involved in its metabolic pathway
We identified putative sulfate transporter encoding genes from four transport families and, surprisingly, we found no evidence for the presence of ATP-Binding Cassette (ABC)-type sulfate transporters in sulfate-reducing microorganisms (SRM) despite earlier reports (Rabus et al, 2015)

Summary

Introduction

Dissimilatory sulfate reduction is a key metabolic process in anoxic environments. It is catalyzed by sulfate-reducing microorganisms (SRM), which encompass a diverse group of bacteria and archaea spanning several phylogenetic lineages (Müller et al, 2015). SRM use sulfate as terminal electron acceptor for the oxidation of organic electron donors or hydrogen, thereby producing sulfide, which they release back to the environment (dissimilatory sulfate reduction). Sulfate can be reduced and assimilated for the synthesis of cell material whereby the produced sulfide is incorporated into sulfur-containing compounds like cysteine (assimilatory sulfate reduction). The initial two steps of sulfate metabolism are similar in both dissimilatory and assimilatory pathways of sulfate reduction. Since the sulfate ion cannot enter the cell by passive diffusion, a specialized transport system is required by all sulfate-utilizing microorganisms

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Conclusion