POSTERS - BLAST X - University of Utah

BLAST X Poster #75
EVOLUTION OF CHEMOTAXIS PROTEINS ON A MICRO SCALE
Brian Cantwell and Igor Zhulin
University of Tennessee, Department of Microbiology, Knoxville, TN
Oak Ridge National Laboratory, Joint Institute for Computational Sciences, Oak Ridge, TN
Computational analysis of very closely related genomes offers the advantage of more
accurate tracing of evolutionary events. The chemotaxis system of enteric bacteria Escherichia
coli and Salmonella enterica are extremely well studied, and the availability of over fifty
sequenced genomes of Enterobacteriacea offers an opportunity to determine the
microevolutionary trends in chemotaxis of enterics. Similarly, seventeen sequenced genomes
are available for the family Shewanellaceae for which Shewanella oneidensis MR-1 has been
most studied by genetic and biochemical methods. In this work we examine the evolution of
the chemotaxis systems of the Enterobacteriaceae and Shewanellaceae using computational
biology methods. Protein sequences of chemotaxis proteins and receptors were extracted from
non-redundant database by matching to domain models and organized into orthologous groups
based on reciprocal BLAST hits, genome context, and phylogenetic relationships. All
Enterobacteriacea contain a single set of chemotaxis proteins and chemoreceptors orthologous
to the E. coli Tsr, Tap, and Aer proteins. Most enteric species contain numerous additional
chemoreceptors including multiple orthologs of the E. coli Trg protein. Shewanella species have
one common set of chemotaxis proteins with some species having an additional set of
chemotaxis proteins. Two chemoreceptors are common among all seventeen Shewanella
species with an additional ten chemoreceptors found in at least fifteen of the seventeen
sequenced genomes. To examine the evolutionary trends within chemotaxis proteins, we
compared orthologous proteins by computing pairwise percentage identity and comparing
domains across species, genus, and family lines. As expected, the domains with highest
conservation include the catalytic domains of the core chemotaxis proteins as well as the
signaling subdomain of the chemoreceptors. The most divergent domains include the P2
domains of CheA, sensory domains of chemoreceptors, HAMP domains, and the methylation
subdomains of the Aer proteins.
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