POSTERS - BLAST X - University of Utah

BLAST X Tue. Evening Session
A CHEMOTAXIS-LIKE SIGNALING PATHWAY REGULATES THE EXPRESSION OF
EXTRACELLULAR MATERIALS IN GEOBACTER SULFURREDUCENS
Hoa T. Tran 1 , Derek R. Lovley 2 , and Robert M. Weis 1
Departments of Chemistry 1 and Microbiology 2 , University of Massachusetts, Amherst, MA
01003, USA.
The chemotaxis pathway that regulates cell motility toward chemical attractants is wellstudied
in Escherichia coli. By contrast, multiple chemotaxis clusters have been found in many
other bacteria, and evidence is accumulating that these cells use chemotaxis-like pathways to
regulate diverse cellular functions. The genome of Geobacter sulfurreducens, a δ-
Proteobacterium found predominantly in the Fe(III) reducing zone of sedimentary environment
contains ~70 chemotaxis gene homologs arranged in 6 major clusters. Cluster 5 (Che5) has a
complete set of chemotaxis homologs, including the kinase cheA (1 copy), cheW (2 copies),
cheR (1), cheB (1), cheY (3) and four other non-che genes. There are 34 chemoreceptor
homologs in the genome, but none is found in the Che5 cluster. Che5-type clusters have been
identified in the genomes of several δ-Proteobacteria, yet their functions are not known. Here,
we report that G. sulfurreducens Che5 cluster regulates gene expression, and in particular the
synthesis of extracellular material that is abundant in OmcS and OmcZ, two c-type cytochromes
bound to the outer membrane. OmcS and OmcZ are essential for cell growth in insoluble
electron acceptors and for effective electricity production on electrodes. Deletion mutants of the
homologs of cheW (gsu2218, gsu2220), cheA (gsu2222) and cheR (gsu2215) increased OmcS
production and decreased OmcZ. In contrast, deletion mutants of cheB (gsu2214), one of the
three cheYs (gsu2223) and a non-che gene (gsu2216) decreased OmcS and increased OmcZ
production. The chemoreceptors that signal through these Che5 proteins are hypothesized to
belong to a single MA class. Evidence that supports this idea is based on the phenotypes of
deletion mutants in two mcp genes (gsu1704, and gsu2372), which are similar the cheA mutant.
Wherever the functional parallels can be drawn, the function of the homologues in Geobacter
Che5 signaling pathway is similar to their counterpart in the E. coli chemotaxis pathway. In
addition to changes in OmcS and OmcZ expression, the cheA, cheR and cheW (gsu2220)
mutants promote cell aggregation and overproduce non-PilA filamentous material. Moreover,
microarray data of the cheR mutant, and quantitative RT-PCR data from the other che mutants
indicate that the Che5 cluster alter the expression of ~175 genes. A substantial fraction of
these are predicted to contain export signals that will result in an to extracellular location. Taken
together, these data demonstrate that G. sulfurreducens Che5 cluster, with one class of
chemoreceptors, regulates the extracellular matrix material biosynthesis.
This research was supported by the U.S. Department of Energy Office of Science (BER)
under the Cooperative Agreement No. DE-FC02-02ER63446.
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