C-di-GMP signalling enzymes of the bacterial predator Bdellovibrio bacteriovorus

A unique obligate predator, Bdellovibrio bacteriovorus utilizes other gram-negative bacteria e.g. E.coli and Pseudomonas aeruginosa as prey. It alternates life cycle between host independent 'axenic' and host dependent predatory phases. It attacks and penetrates the cell envelope of prey bacteria and multiply within their periplasm. When nutritional resources gets exhausted, it ruptures prey cell envelope and release themselves as motile 'attack phase' cells to start new infection cycle. In bacteria, a secondary messenger c-di-GMP regulates variety of biological processes. C-di-GMP also contributes to bacterial life styles transition from unicellular, motile cell to surface attached, multi-cellular communities (biofilms) and controls the switch between environmental and pathogenic lifestyles in other organisms. Hence, we investigated the possible role of c-di-GMP in lifestyle switching in B. bacteriovorus. The bioinformatics analysis identified 5 GGDEF and 1 EAL domain proteins encoded by B. bacteriovorus genome followed by their expression and purification for biochemical characterization. In vitro assays showed that DgcA, DgcB, and DgcC were diguanylyl cyclases and DgcD, CdgA were inactive proteins. But CdgA was found to act as a c-di-GMP receptor. In this collaborative study, another group found some interesting results that inactivation of individual GGDEF domain genes resulted in remarkably distinct phenotypes. In conclusion, this biochemical and genetic approach based study successfully determined functional presence of c-di-GMP signaling enzymes with distinctly different role in life style switching decision in B. bacteriovorus .