Aliivibrio logei

Aliivibrio logei represents the cold-water counterpart to Vibrio fischeri's temperate lifestyle. Both bacteria form bioluminescent symbioses with squid, but they've partitioned the ocean thermally: V. fischeri dominates warm waters while A. logei colonizes cold-water squid species in polar and deep-sea environments. This parallel evolution of the same ecological strategy across temperature regimes reveals how environmental constraints shape competitive boundaries.

The squid-Vibrio symbiosis evolved independently multiple times, but the bacterial partners consistently come from the same Vibrionaceae family. A. logei's adaptation to cold waters required modifications throughout its physiology—membrane composition, enzyme kinetics, and protein stability all adjusted for low-temperature function. The core quorum sensing and bioluminescence machinery remained conserved; the surrounding cellular infrastructure adapted. This pattern—conserved functional modules within adapted cellular contexts—mirrors how successful innovations spread across organizations serving different markets.

A. logei also demonstrates the importance of competitive exclusion in symbiosis. Squid light organs are typically colonized by a single bacterial species despite exposure to diverse marine microbiota. A. logei and V. fischeri cannot coexist in the same light organ; whichever colonizes first excludes the other. Temperature determines which species arrives first and grows faster, creating geographic zones of dominance. The symbiosis isn't just bacteria and squid—it's a three-way interaction where temperature sets the competitive boundary between potential bacterial partners.