Project description:In this study, we investigated Mn3+-cycling microbial populations enriched from Lake Matano, Indonesia using metagenomics and metaproteomics. Lake Matano contains an active Mn cycle that links the oxic-anoxic interface with anoxic deep waters that are enriched in iron and manganese, and depleted in sulfate, phosphate, and oxidized nitrogen (Crowe et al., 2008; Jones et al., 2011). Sediments were incubated with sequential transfers for ~1 year with Mn3+ as the sole electron acceptor and methane as organic carbon until achieving sediment-free conditions. Here we investigate this novel species of Dechloromonas (Betaproteobacteria), “Candidatus Dechloromonas occultata,” which was the dominant population in enrichment cultures with active Mn3+ reduction. “Ca. D. occultata” expressed electron conduits related to those involved in Fe2+ oxidation (Mto-like), as well as a novel cytochrome c-rich gene cluster putatively involved in extracellular electron transfer, and an atypical nitrous oxide reductase. According to ribosomal counts, Dechloromonas outnumber Geobacter. In terms of functional genes, Dechloromonas expresses a wider variety and number of genes. Dechloromonas therefore seems to have a (selective?) advantage over Geobacter. Previous experiments revealed that Dechloromonas express nitrogen regulators, reductases and scavenging genes, as well as many carbon central metabolic pathways, and aromatic carbon degradation pathways. Dechloromonas is a beta proteobacteria, and these are "experts" in nitrogen metabolism. Geobacter, on the other hand, is well known for carbon degradation. Our previous experiments lead to our hypothesis that Dechloromonas is more active because they are more successful at acquiring nitrogen, a limiting nutrient for Geobacter. This would further suggest that carbon is not the limiting nutrient. We will test 2 hypotheses with the next suite of experiments 1) pyrophosphate supports the community, by allowing carbon fixation , 2)Dechloromonas has a (selective?) advantage over Geobacter. To test this hypothesis, bioreactors will be used to grow biotriplicate cultures of (1)- CH4 vs. pyrophosphate and (2)-CH4 vs. Mn(III) pyrophosphate. Here we have analyzed whole cell pellets using gas phase fractionations on the Q Exactive. Are Dechloromonas capable of out-competing Geobacter when grown in media with methane as the only carbon source bioreactors because they are capable of acquiring more nitrogen? Source of inoculum. Lake Matano is a metal-rich, ancient ocean analog (Crowe et al. 2011, Jones et al. 2011). Organic carbon in Lake Matano is mostly mineralized via methanogenesis before reaching the iron-rich sediments, limiting organic matter bioavailability for metal-reducers (Kuntz et al. 2015). A 15-cm sediment core from 200 m water depth in Lake Matano, Sulawesi Island, Indonesia (02°26′27.1′′S, 121°15′12.3′′E; in situ sediment temperature ~27°C) was sampled in November 2014 and sub-sampled at 5 cm increments. Sediments were sealed in gas-tight Mylar bags with no headspace (Hansen et al. 2000) and stored at 4°C until incubations began in December 2015.

Project description:Whole-genome DNA microarray analysis of Geobacter sulfurreducens cells grown on Fe(III)-oxide or Mn(IV)-oxide versus cells grown on soluble Fe(III) citrate indicated that there were significant differences in transcription patterns during growth on the insoluble metal oxides compared to growth on soluble Fe(III). Many of the genes that appeared to be up-regulated during growth on the metal hydroxides were involved in electron transport. The most highly up-regulated genes for both conditions were omcS and omcT, which encode co-transcribed c-type cytochromes exposed on the outer surface of the cell that are known to be required for Fe(III) and Mn(IV)-oxide reduction. Other electron transport genes that were up-regulated on both insoluble metals included the gene coding for the outer membrane c-type cytochrome, OmcG, genes for the outer membrane proteins, OmpB and OmpC, and the gene that codes for the structural protein of electrically conductive pili, PilA. Genes that were up-regulated in cells grown on Fe(III)-oxide but not Mn(IV)-oxide, included outer membrane c-type cytochromes including OmcE, a putative DMSO reductase protein, and proteins from the cytochrome bc1 complex. Electron transport genes that were only up-regulated in Mn(IV)-oxide grown cells included the genes that code for the outer membrane c-type cytochromes, OmcZ and OmcB, the periplasmic c-type cytochrome, MacA, and fumarate reductase. Genetic studies indicated that the c-type cytochrome proteins, PpcH, OmcJ, OmcM, OmcV, MacA, OmcF, OmcI, and OmcQ, and the iron sulfur subunit of the cytochrome b/b6 complex, QcrA, are important for reduction of insoluble Fe(III)-oxides but do not appear to be important for Mn(IV) reduction. These results demonstrate that the physiology of Fe(III) reducing bacteria differ significantly during growth on insoluble electron and soluble electron acceptors and emphasizes the importance of c-type cytochromes in extracellular electron transfer in G. sulfurreducens. Geobacter sulfurreducens cells were grown with acetate (5 mM) provided as the electron donor and either Fe(III) oxide or Fe(III) citrate provided as the electron acceptor. Cells were harvested at mid-log and total RNA was extracted. Total RNA (0.5 M-NM-<g) was amplified using the MessageAmp II-Bacteria Kit (Ambion, Foster City, CA) according to the manufacturers instructions. Ten micrograms of amplified RNA (aRNA) was chemically labeled with Cy3 (for the control or soluble electron acceptor condition) or Cy5 (for the experimental or insoluble electron acceptor condition) dye using the MicroMax ASAP RNA Labeling Kit (Perkin Elmer, Wellesley, MA) according to the manufacturerM-bM-^@M-^Ys instructions. RNA samples from three biological replicates were hybridized in duplicate on 12K Combimatrix antisense-detecting arrays. The experimental condition (DL1 grown with Mn(IV) oxide as acceptor) was labeled with cy5, the control condition (DL1 grown with Fe(III) citrate as acceptor) was labeled with cy3

Project description:Whole-genome DNA microarray analysis of Geobacter sulfurreducens cells grown on Fe(III)-oxide or Mn(IV)-oxide versus cells grown on soluble Fe(III) citrate indicated that there were significant differences in transcription patterns during growth on the insoluble metal oxides compared to growth on soluble Fe(III). Many of the genes that appeared to be up-regulated during growth on the metal hydroxides were involved in electron transport. The most highly up-regulated genes for both conditions were omcS and omcT, which encode co-transcribed c-type cytochromes exposed on the outer surface of the cell that are known to be required for Fe(III) and Mn(IV)-oxide reduction. Other electron transport genes that were up-regulated on both insoluble metals included the gene coding for the outer membrane c-type cytochrome, OmcG, genes for the outer membrane proteins, OmpB and OmpC, and the gene that codes for the structural protein of electrically conductive pili, PilA. Genes that were up-regulated in cells grown on Fe(III)-oxide but not Mn(IV)-oxide, included outer membrane c-type cytochromes including OmcE, a putative DMSO reductase protein, and proteins from the cytochrome bc1 complex. Electron transport genes that were only up-regulated in Mn(IV)-oxide grown cells included the genes that code for the outer membrane c-type cytochromes, OmcZ and OmcB, the periplasmic c-type cytochrome, MacA, and fumarate reductase. Genetic studies indicated that the c-type cytochrome proteins, PpcH, OmcJ, OmcM, OmcV, MacA, OmcF, OmcI, and OmcQ, and the iron sulfur subunit of the cytochrome b/b6 complex, QcrA, are important for reduction of insoluble Fe(III)-oxides but do not appear to be important for Mn(IV) reduction. These results demonstrate that the physiology of Fe(III) reducing bacteria differ significantly during growth on insoluble electron and soluble electron acceptors and emphasizes the importance of c-type cytochromes in extracellular electron transfer in G. sulfurreducens. Geobacter sulfurreducens cells were grown with acetate (5 mM) provided as the electron donor and either Fe(III) oxide or Fe(III) citrate provided as the electron acceptor. Cells were harvested at mid-log and total RNA was extracted. Total RNA (0.5 M-NM-<g) was amplified using the MessageAmp II-Bacteria Kit (Ambion, Foster City, CA) according to the manufacturers instructions. Ten micrograms of amplified RNA (aRNA) was chemically labeled with Cy3 (for the control or soluble electron acceptor condition) or Cy5 (for the experimental or insoluble electron acceptor condition) dye using the MicroMax ASAP RNA Labeling Kit (Perkin Elmer, Wellesley, MA) according to the manufacturerM-bM-^@M-^Ys instructions. RNA samples from three biological replicates were hybridized in duplicate on 12K Combimatrix antisense-detecting arrays. The experimental condition (DL1 grown with Fe(III) oxide as acceptor) was labeled with cy5, the control condition (DL1 grown with Fe(III) citrate as acceptor) was labeled with cy3

Project description:The ability of Geobacter species to readily donate electrons to extracellular electron acceptors makes the study of their physiology not only important for the understanding of environmental processes, but also for industrial applications such as bioelectronics and electrosynthesis. Studies in G. sulfurreducens have shown that outer surface components, such as c-type cytochromes and conductive type IV pili play an important role in direct electron transfer to extracellular electron acceptors such as Fe(III) oxides and electrodes. However, many of these thoroughly studied outer surface components, including c-type cytochromes, are not well conserved among Geobacter species. In order to better understand which components are involved in extracellular electron transfer in Geobacter species other than G. sulfurreducens, studies were conducted with its close relative G. metallireducens. Whole-genome microarray analysis revealed that 23 of the 91 putative c-type cytochromes encoded in the G. metallireducens genome were upregulated at least 2-fold in cells grown with Fe(III) oxide compared to cells in which Fe(III) citrate was provided as the terminal electron acceptor. Protein identification with liquid-chromatography/mass spectrometry detected 6 c-type cytochromes that were more abundant in the outer surface cell fraction of cells that were grown with Fe(III) oxide as the terminal electron acceptor compared to cells grown on Fe(III) citrate. 22 genes encoding c-type cytochromes were chosen for gene deletion. Deletion of 6 genes encoding for c-type cytochromes, a gene encoding for a lipopolysaccharide biosynthesis-associated protein, and a gene encoding for a NHL- repeat containing protein inhibited growth when Fe(III) oxide was provided as the electron acceptor. This study suggests that there are different roads for extracellular electron transfer in Geobacteraceae since homologous c-type cytochromes have different functions from one species to the other, and novel components not previously found to be essential for extracellular electron transfer were identified. An eight-chip study using total RNA recovered from four separate cultures of Geobacter metallireducens GS-15 grown with acetate (10mM)-Fe(III) oxide (100 mmol l-1) (experimental condition) or with acetate (10 mM)-Fe(III) citrate (55mM) (control condition) during exponential growth. Each chip measures the expression level of 3,627 genes from Geobacter metallireducens GS-15 with nine 45-60-mer probe pairs (PM/MM) per gene, with three-fold technical redundancy.

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Bioreactor sludge metagenome

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