Biomedical subjects
Lisa Crossman
Publications and source records attributed to Lisa Crossman.
Biofilm dispersal in Xanthomonas campestris is controlled by cell-cell signaling and is required for full virulence to plants.
The rpf gene cluster of Xanthomonas campestris pathovar campestris (Xcc) is required for the pathogenesis of this bacterium to plants. Several rpf genes are involved in the coordinate positive regulation of the production of virulence factors mediated by the small diffusible molecule DSF (for diffusible signal factor). RpfF directs the synthesis of DSF, and a two-component sensory transduction system comprising RpfC and RpfG has been implicated in the perception of the DSF signal and signal transduction. In L medium, rpfF, rpfG, rpfC, and rpfGHC mutants grew as matrix-enclosed aggregates, whereas the wild type grew in a dispersed planktonic fashion. Synthesis of the extracellular polysaccharide xanthan was required for aggregate formation. Addition of DSF triggered dispersion of the aggregates formed by the rpfF strain, but not those of rpf strains defective in DSF signal transduction. An extracellular enzyme from Xcc whose synthesis was positively controlled by the DSF/rpf system could disperse the aggregates produced by all rpf strains. The enzyme was identified as the single endo-beta-1,4-mannanase encoded by the Xcc genome. This enzyme had no detectable activity against soluble xanthan. The endo-beta-1,4-mannanase was required for the full virulence of Xcc to plants. On the basis of this model system, we propose that one role of the beta-mannanase during disease is to promote transitions from an aggregated or biofilm lifestyle to a planktonic lifestyle in response to the DSF signal.
The value of comparison.
With the number of published microbial genomes now in excess of 100, any new genome that is sequenced is likely to have a close relative available for comparison. Indeed, it is increasingly difficult to perform any genomic analysis that is not comparative. This should, however, not be seen as a drawback; it is often the case that a large amount of information can be drawn from these comparisons, especially between closely related organisms. Several genome sequences published recently indicate the value of comparisons at the genomic level.
Pathogenomics.
The genomes described this month reflect the overall historical bias of microbial genomics towards pathogenic bacteria. Although the balance is now being redressed to some extent, especially through the study of extremophiles, it is still the case that the opportunities provided by genomic studies are primarily taken up by those who study bacterial pathogenicity. This part of the field is, however, being broadened by including the study of pathogens of animals, insects and plants alongside those that afflict humans.