DSSS - Coordination of Phase Variation-mediated Bet-Hedging and Two Component Signal Transduction in Burkholderia thailandensis

Phase Variation (PV) and Two Component Signal Transduction (TCS) are two mechanisms used by bacteria to survive diverse environmental conditions. While TCS systems allow all bacteria in the population to sense and respond to changes in conditions, PV creates a genotypically and phenotypically heterogeneous population with subpopulations optimized to persist when conditions change, or are encountered, suddenly. We identified a PV system in Burkholderia thailandensis in which RecA-mediated homologous recombination between a pair of insertion sequence (IS) 2-like elements duplicates a 208.6 kb region that contains 157 coding sequences. RecA-mediated homologous recombination also resolves merodiploids, and hence copy number of the region is varied and dynamic. The presence of two or more copies of the region is advantageous for growth in a biofilm, while a single copy is advantageous during planktonic growth. This system represents a rare example of IS element-mediated evolution in which the IS elements provide homologous sequences for amplification of a chromosomal region that provides a selective advantage under specific growth conditions, representing a bet-hedging strategy and expanding the lifestyle repertoire of the species. Further analyses revealed TCS system-encoding genes within the region that are also required for biofilm formation. Hence, B. thailandensis coordinates PV and TCS to ensure population survival under ever-changing environmental conditions. This research was conducted by a creative and independently-thinking graduate student who disproved several of the lab’s hypotheses for how and why the system functions, serving as an inspiration for trainees at all levels.