Vibrio harveyi

Vibrio harveyi has become the premier model for understanding complex quorum sensing because it uses not one but three parallel communication systems. While Vibrio fischeri pioneered our understanding of bacterial communication through its relatively simple LuxI/LuxR system, V. harveyi revealed that bacteria can integrate multiple signals simultaneously—essentially running three different surveys of population density and combining the results before making decisions.

The three systems use different signaling molecules: an acyl-homoserine lactone (like V. fischeri uses), a furanosyl borate diester (AI-2, which many bacterial species produce), and a species-specific signal. Each channel converges on a shared regulatory phosphorelay, creating a biological logic gate that integrates information from multiple sources. High signal on any single channel isn't sufficient to trigger quorum responses; the bacterium requires concordant information across systems before committing to collective behaviors.

This multi-channel architecture provides robustness and precision that single-channel systems cannot match. Noise or manipulation on one channel doesn't trigger false responses. The AI-2 channel, recognizable by many bacterial species, enables V. harveyi to sense total bacterial population regardless of species composition. The species-specific channels reveal how many of those bacteria are V. harveyi. By integrating these signals, the bacterium distinguishes between 'many bacteria present' and 'many of us present'—a crucial distinction for deciding whether to invest in species-specific behaviors like bioluminescence.