Identifying Genes Involved in Lactose Metabolism in Caulobacter crescentus by Transposon Mutagenesis

Because it flourishes in aquatic environments with low nutrient levels, Caulobacter crescentus serves as an advantageous model for understanding the metabolic capacities of oligotrophic bacteria.  Recent genetic analysis revealed that C. crescentus uses an atypical pathway for lactose catabolism and hinted at the existence of unknown enzymes.  To identify additional factors involved in this alternate metabolic pathway, we performed transposon mutagenesis and screened approximately 12,000 insertion mutants for those that were incapable of growing on minimal media with lactose as the only carbon source.  The screen yielded 20 isolates that showed the desired phenotype, with varying degrees of ability to utilize other sugars, such as cellobiose and xylose.  We are currently identifying the genomic location of these transposon insertions.  Preliminary results suggest novel contributors to a previously obscure pathway.  Therefore, this study expands the already diverse repertoire of metabolic activities performed by bacterial species.