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Comparative Genomic Evidence for a Close Relationship between the Dimorphic Prosthecate Bacteria Hyphomonas neptunium and Caulobacter crescentus

The Institute for Genomic Research, Rockville, Maryland 20850,¹ Department of Microbiology, University of Georgia, Athens, Georgia 30602,² Department of Biology, Indiana University, Bloomington, Indiana 47405,³ Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, Maryland 20742,⁴ Bauer Center for Genomics Research, Harvard University, Cambridge, Massachusetts 02138,⁵ Department of Biochemistry, Cellular and Molecular Biology and Microbiology, University of Tennessee, Knoxville, Tennessee 37996,⁶ Center of Marine Biotechnology, Baltimore, Maryland 21202⁷

Received 20 January 2006/ Accepted 4 July 2006

The dimorphic prosthecate bacteria (DPB) are -proteobacteria that reproduce in an asymmetric manner rather than by binary fission and are of interest as simple models of development. Prior to this work, the only member of this group for which genome sequence was available was the model freshwater organism Caulobacter crescentus. Here we describe the genome sequence of Hyphomonas neptunium, a marine member of the DPB that differs from C. crescentus in that H. neptunium uses its stalk as a reproductive structure. Genome analysis indicates that this organism shares more genes with C. crescentus than it does with Silicibacter pomeroyi (a closer relative according to 16S rRNA phylogeny), that it relies upon a heterotrophic strategy utilizing a wide range of substrates, that its cell cycle is likely to be regulated in a similar manner to that of C. crescentus, and that the outer membrane complements of H. neptunium and C. crescentus are remarkably similar. H. neptunium swarmer cells are highly motile via a single polar flagellum. With the exception of cheY and cheR, genes required for chemotaxis were absent in the H. neptunium genome. Consistent with this observation, H. neptunium swarmer cells did not respond to any chemotactic stimuli that were tested, which suggests that H. neptunium motility is a random dispersal mechanism for swarmer cells rather than a stimulus-controlled navigation system for locating specific environments. In addition to providing insights into bacterial development, the H. neptunium genome will provide an important resource for the study of other interesting biological processes including chromosome segregation, polar growth, and cell aging.

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