Global transcriptional analysis of Geobacter sulfurreducens gsu1771-mutant in response to biofilm development in different supports

The formation of electroactive biofilms is a crucial process for the generation of bioelectricity and bioremediation. G. sulfurreducens is a dissimilatory metal-reducing microorganism that can couple oxidation of organic matter with extracellular electron transfer to different insoluble electron acceptors. It has the capability to form biofilms in insoluble metal oxides and electroconductive biofilms in electrodes in bioelectrochemical systems. The formation of electroactive biofilms in this microorganism is a process that has been studied from a physiological, genetic, physical, and electrochemical approach. In G. sulfurreducens, we found that the transcriptional regulator GSU1771 participates in the gene expression of essential genes involved in electron transfer and biofilm formation. Strains deficient in GSU1771 increases Fe(III) reduction, produces more c-type cytochromes and exopolysaccharides. Furthermore, the biofilms produced are thicker and more electroactive than wild-type. In this work, we investigate the global gene expression profile performing RNA-seq comparing ?gsu1771 mutant biofilm grown in non-conductive support (glass) and respiring-graphite electrode. RNA-seq analysis of ?gsu1771 biofilm grown in glass support revealed a total of 467 (167 upregulated and 300 downregulated) differentially expressed genes versus the wild-type biofilm. Meanwhile, in ?gsu1771 biofilm developed in respiring-electrode graphite, we detect 119 (79 upregulated and 40 downregulated) differentially expressed genes with respect to wild-type biofilm. Moreover, transcriptional changes of 67 (56 with the same regulation and in 11 counterregulation) genes were shared in ?gsu1771 biofilm developed in glass and graphite electrodes. We locate upregulated in ?gsu1771 biofilms potential target genes, involved in exopolysaccharide synthesis (gsu1961-63, gsu1959, gsu1972-73, gsu1976-77). We confirmed the upregulation of gsu1979, gsu0972, gsu0783, pgcA, omcM, aroG, panC gnfK, gsu2507, and the downregulation of asnA, ato-1, gsu0810, pilA, csrA, ppcD, and gsu3356 genes by RT-qPCR. DNA-protein binding assay shows direct binding of the GSU1771 regulator to the promoter region of pgcA, pulF, relA, and gsu3356. Also, heme-staining and western blotting revealed an increase of c-type cytochromes in ?gsu1771 biofilms such as OmcS and OmcZ. In general, our data shows that GSU1771 is a global regulator involved in controlling the extracellular electron transfer and exopolysaccharide synthesis, processes required for electroconductive biofilm development. Overall design: Comparative gene expression profiling analysis of RNA-seq data for Geobacter sulfurreducens biofilm from wild type and gsu1771-mutant strains grown on a glass support and graphite electrode. From each sample, experimental duplicates were used.