Identification of an extracellular polysaccharide network essential for cytochrome anchoring and biofilm formation in Geobacter sulfurreducens

Janet B. Rollefson, Camille S. Stephen, Ming Tien, Daniel R. Bond

Research output: Contribution to journalArticle

108 Citations (Scopus)

Abstract

Transposon insertions in Geobacter sulfurreducens GSU1501, part of an ATP-dependent exporter within an operon of polysaccharide biosynthesis genes, were previously shown to eliminate insoluble Fe(III) reduction and use of an electrode as an electron acceptor. Replacement of GSU1501 with a kanamycin resistance cassette produced a similarly defective mutant, which could be partially complemented by expression of GSU1500 to GSU1505 in trans. The Δ1501 mutant demonstrated limited cell-cell agglutination, enhanced attachment to negatively charged surfaces, and poor attachment to positively charged poly-D-lysine- or Fe(III)-coated surfaces. Wild-type and mutant cells attached to graphite electrodes, but when electrodes were poised at an oxidizing potential inducing a positive surface charge (+0.24 V versus the standard hydrogen electrode [SHE]), Δ1501 mutant cells detached. Scanning electron microscopy revealed fibrils surrounding wild-type G. sulfurreducens which were absent from the Δ1501 mutant. Similar amounts of type IV pili and pilus-associated cytochromes were detected on both cell types, but shearing released a stable matrix of c-type cytochromes and other proteins bound to polysaccharides. The matrix from the mutant contained 60% less sugar and was nearly devoid of c-type cytochromes such as OmcZ. The addition of wild-type extracellular matrix to Δ1501 cultures restored agglutination and Fe(III) reduction. The polysaccharide binding dye Congo red preferentially bound wild-type cells and extracellular matrix material over mutant cells, and Congo red inhibited agglutination and Fe(III) reduction by wild-type cells. These results demonstrate a crucial role for the xap (extracellular anchoring polysaccharide) locus in metal oxide attachment, cell-cell agglutination, and localization of essential cytochromes beyond the Geobacter outer membrane.

Original languageEnglish (US)
Pages (from-to)1023-1033
Number of pages11
JournalJournal of bacteriology
Volume193
Issue number5
DOIs
StatePublished - Mar 1 2011

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Geobacter
Cytochromes
Biofilms
Polysaccharides
Agglutination
Electrodes
Cytochrome c Group
Congo Red
Extracellular Matrix
Kanamycin Resistance
Graphite
Operon
Electron Scanning Microscopy
Oxides
Lysine
Hydrogen
Coloring Agents

All Science Journal Classification (ASJC) codes

  • Microbiology
  • Molecular Biology

Cite this

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title = "Identification of an extracellular polysaccharide network essential for cytochrome anchoring and biofilm formation in Geobacter sulfurreducens",
abstract = "Transposon insertions in Geobacter sulfurreducens GSU1501, part of an ATP-dependent exporter within an operon of polysaccharide biosynthesis genes, were previously shown to eliminate insoluble Fe(III) reduction and use of an electrode as an electron acceptor. Replacement of GSU1501 with a kanamycin resistance cassette produced a similarly defective mutant, which could be partially complemented by expression of GSU1500 to GSU1505 in trans. The Δ1501 mutant demonstrated limited cell-cell agglutination, enhanced attachment to negatively charged surfaces, and poor attachment to positively charged poly-D-lysine- or Fe(III)-coated surfaces. Wild-type and mutant cells attached to graphite electrodes, but when electrodes were poised at an oxidizing potential inducing a positive surface charge (+0.24 V versus the standard hydrogen electrode [SHE]), Δ1501 mutant cells detached. Scanning electron microscopy revealed fibrils surrounding wild-type G. sulfurreducens which were absent from the Δ1501 mutant. Similar amounts of type IV pili and pilus-associated cytochromes were detected on both cell types, but shearing released a stable matrix of c-type cytochromes and other proteins bound to polysaccharides. The matrix from the mutant contained 60{\%} less sugar and was nearly devoid of c-type cytochromes such as OmcZ. The addition of wild-type extracellular matrix to Δ1501 cultures restored agglutination and Fe(III) reduction. The polysaccharide binding dye Congo red preferentially bound wild-type cells and extracellular matrix material over mutant cells, and Congo red inhibited agglutination and Fe(III) reduction by wild-type cells. These results demonstrate a crucial role for the xap (extracellular anchoring polysaccharide) locus in metal oxide attachment, cell-cell agglutination, and localization of essential cytochromes beyond the Geobacter outer membrane.",
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Identification of an extracellular polysaccharide network essential for cytochrome anchoring and biofilm formation in Geobacter sulfurreducens. / Rollefson, Janet B.; Stephen, Camille S.; Tien, Ming; Bond, Daniel R.

In: Journal of bacteriology, Vol. 193, No. 5, 01.03.2011, p. 1023-1033.

Research output: Contribution to journalArticle

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