A locus necessary for the transport and catabolism of erythritol in Sinorhizobium meliloti

Abstract

In this work we have genetically defined an erythritol utilization locus in Sinorhizobium meliloti. A cosmid containing the locus was isolated by complementation of a transposon mutant and was subsequently mutagenized using Tn5 : : B20. The locus was found to consist of five transcriptional units, each of which was necessary for the utilization of erythritol. Genetic complementation experiments using genes putatively annotated as erythritol catabolic genes clearly showed that, of the 17 genes at this locus, six genes are not necessary for the utilization of erythritol as a sole carbon source. The remaining genes encode EryA, EryB, EryC and TpiB as well as an uncharacterized ABC-type transporter. Transport experiments using labelled erythritol showed that components of the ABC transporter are necessary for the uptake of erythritol. The locus also contains two regulators: EryD, a SorC class regulator, and SMc01615, a DeoR class regulator. Quantitative RT-PCR experiments showed that each of these regulators negatively regulates its own transcription. In addition, induction of the erythritol locus was dependent upon EryD and a product of erythritol catabolism. Further characterization of polar mutations revealed that in addition to erythritol, the locus contains determinants for adonitol and l-arabitol utilization. The context of the mutations suggests that the locus is important for both the transport and catabolism of adonitol and l-arabitol.