Researchers from Penn State University have conducted a study on the fascinating relationship between bioluminescent bacteria (Vibrio fischeri) and the Hawaiian bobtail squid. This mutualistic bond involves the bacteria living in a specialized light organ within the squid, providing the squid with camouflage from predators while receiving nutrients from the squid in return.
The team discovered that the bacteria coordinate their actions within the light organ through a process called “quorum sensing.” As the bacterial population increases, they release signaling molecules that reach a threshold concentration, triggering a switch in behavior. Once a quorum is reached, the bacteria begin producing bioluminescence and suppress their motility, settling within the squid’s light organ.
Before colonization, the bacteria form large cell aggregates, which raised the question of how they avoid activating the quorum sensing pathway prematurely. The researchers found that during aggregation, the bacteria produce a small RNA molecule called Qrr1, which is usually suppressed by quorum sensing. This allows the bacteria to remain motile and non-bioluminescent while outside the squid.
The study also revealed that Qrr1 is crucial for promoting colonization. Surprisingly, despite the similarities to the quorum sensing pathway, Qrr1 remains active during aggregation, thanks to a transcription factor called SypG, which controls both aggregation-related genes and Qrr1 expression.
The researchers believe that this complex regulatory system is widespread among symbiotic bacteria and plays a vital role in coordinating the shift from colonization to bioluminescence. Understanding these mechanisms is essential for comprehending how bacteria colonize their hosts in various ecosystems.
Source: Pennsylvania State University