Short introduction to current research topic:

Acidovorax radicis N35, an AHL-producing root-associated bacterium able to perform phenotypic variation

A. radicis N35 is a β-proteobacterium, isolated from surface sterilized wheat roots. This bacterium undergoes phenotypic variation from the original rough colony shape on agar plates and flock formation in liquid medium to smooth colonies on agar plates without flocculation in liquid medium (N35v). A plant growth promoting effect with barley was demonstrated using both phenotypic forms in green house experiments showing more pronounced effects with the original form N35. The original type of cells showed a dominant colonization behavior on roots when coinoculated with N35v.
AHL quorum sensing molecules with the structure 3-hydroxy-decanoyl homoserine lactone were detected as the major autoinducer signaling substance using a fourier transformation ion cyclotron resonance mass spectrometer (FTICR/MS). To find out genetic variations between the two forms and in order to identify the AHL synthesis gene, the whole genomes of both phenotypes were sequenced with a 454 pyrosequencer (Roche). The same sequence stretch of 555 nucleotides encoding an AHL synthase protein was identified in both phenotypic variants. Targeted mutagenesis yielded knock-out mutants of the AHL-synthase of N35, which were unable to flocculate and undergo phenotypic variation. In addition, several AHL-regulated properties, such as siderophore and lipase production were lost in these mutants.
After analysis of the whole genome data, only very few differences between wild-type and variant could be detected. Interestingly, a 16 nucleotides deletion region was identified in the N35v genome compared to N35. This region shows high sequence similarity to the mismatch repair protein MutL. This protein is truncated in N35v and thus MutL might be directly or indirectly responsible for the differences in gene expression between the two variants.

back