Unknown,Transcriptomics,Genomics,Proteomics

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Desulfitobacterium hafniense DCB-2 Gene Expression Differences from Pyruvate Fermentation when Grown with Ferric Citrate, Selenate, Nitrate, or Uranyl Acetate

ABSTRACT: Desulfitobacterium hafniense DCB-2, a halo-respirer and versatile inorganic ion reducer, grows in hazardous waste contaminated environments. M-BM- Gene expression changes were determined when the strain was grown in the presence of high concentrations of Fe(+3), Se(+6), U(+6), or NO3(-) as alternative electron acceptors. (Thesis by Christina L. Harzman at Michigan State University, 2009) RNA was used to directly compare gene expression in control samples of pyruvate fermentation (20 mM) to fermentation in the presence inorganic electron acceptors or respiration-inducing conditions. M-BM- The inorganic electron acceptors added to media for fermentation were 1 mM selenate or 0.5 mM uranyl acetate. The respiration-inducing conditions were 50 mM ferric citrate (20 mM lactate carbon source) or 10 mM nitrate (20 mM lactate carbon source). Microarray hybridizations were performed with a dye swap and 3 biological replicates for a total of 6 slides per condition for comparison.

ORGANISM(S): Desulfitobacterium hafniense DCB-2

SUBMITTER: Christina Harzman

PROVIDER: E-GEOD-33988 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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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.

Project description:Shewanella oneidensis MR-1 is a facultative anaerobe that grows by respiration using a variety of electron acceptors. This organism serves as a model to study how bacteria thrive in redox-stratified environments. A glucose-utilizing engineered derivative of MR-1 has been reported to be unable to grow in glucose minimal medium (GMM) in the absence of electron acceptors, despite this strain having a complete set of genes for reconstructing glucose to lactate fermentative pathways. To gain insights into why MR-1 is incapable of fermentative growth, this study examined a hypothesis that this strain is programmed to repress the expression of some carbon metabolic genes in the absence of electron acceptors. Comparative transcriptomic analyses of the MR-1 derivative were conducted in the presence and absence of fumarate as an electron acceptor, and these found that the expression of many genes involved in carbon metabolism required for cell growth, including several tricarboxylic acid (TCA) cycle genes, was significantly downregulated in the absence of fumarate. This finding suggests a possibility that MR-1 is unable to grow fermentatively on glucose in minimal media owing to the shortage of nutrients essential for cell growth, such as amino acids. This idea was demonstrated in subsequent experiments that showed that the MR-1 derivative fermentatively grows in GMM containing tryptone or a defined mixture of amino acids. We suggest that gene regulatory circuits in MR-1 are tuned to minimize energy consumption under electron acceptor-depleted conditions, and that this results in defective fermentative growth in minimal media. IMPORTANCE It is an enigma why S. oneidensis MR-1 is incapable of fermentative growth despite having complete sets of genes for reconstructing fermentative pathways. Understanding the molecular mechanisms behind this defect will facilitate the development of novel fermentation technologies for the production of value-added chemicals from biomass feedstocks, such as electro-fermentation. The information provided in this study will also improve our understanding of the ecological strategies of bacteria living in redox-stratified environments.

Dataset Information

Desulfitobacterium hafniense DCB-2 Gene Expression Differences from Pyruvate Fermentation when Grown with Ferric Citrate, Selenate, Nitrate, or Uranyl Acetate

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