Vibrio harveyi Associated with Aglaophenia octodonta (Hydrozoa, Cnidaria)

Microbial Ecology, November, 2006
Volume 52(4) 603-608

Classically, Vibrio harveyi is thought of as a symbiote of squid. It's light production is a clear benefit to the squid as a form of camouflage and the symbiosis is very specialized. However, the luciferase light production system is much more broadly distributed in nature, and further more, V. harveyi live in the water column and other place, away from the squid.

This paper highlights an alternative symbiosis - or is it simply an association? Are the V. harveyi on this hydrozoa the same way they would be on a rock? Is it just a surface for colonization? Or is there a real colonization specific to the hydrozoa? Is it beneficial to the hydrozoa as well as squid, or for the hydrozoa, are the vibrio just parasites, conveniently tamed by the squid?

First, let me express my extreme jealousy at the guys who had the job of scuba diving off the coast of Apulia, Italy, home of much wonderful food...

The choice of buffered peptone, a waring blender, and 2216 Marine Agar are all fairly standard. This isolation strategy was paired with microscopic observation, but no direct molecular techniques. In so much as it was a simple recovery operation, the methods used appear completely sufficient to achieve their end. However, we can't suggest that the complete diversity was recovered.

What seems odd is the choice to move from a partial 16S sequence to a series of 'Bergey's' style phenotypic tests for strain identification. After all, with isolates in hand, it might have been trivial to sequence the RecA (see Phylogeny of Vibrio cholerae Based on recA Sequence; Infection and Immunity, Stine et al 2000, 68 (12) 7180...). Hsp60 could have been used equally well. Or maybe a nice MLSA strategy could have been pursued (Journal of Clinical Microbiology, May 2003, p. 2191-2196, Vol. 41, No. 5; Journal of Clinical Microbiology, March 2004, p. 1280-1282, Vol. 42, No. 3). Given the right 3 or so genes, they might have great confidence in the outcome.

Regardless, they found a fluorescing vibrio colonizing the cnidarians. Other cnidarians produce their own light, but this one does not, and perhaps the bacteria provide this function. Did colonization relax the selection on light production and obviate the native luminescence? Or did the loss come first? How useful is the light, how much is produced by the bacteria and how does it compare?

Also, there is speculation in the article about the role of chitinases... but no real follow up. It is certainly a pain to produce flakes of squid pen and test for growth on chitin in minimal media, but it could clarify whether these bacteria actually can eat the chitin.

Still, we need experiments with antitbiotics and such to test whether the cnidarians are helped or harmed by these colonists. It would also be nice to see a sampling of diverse cnidarians at a few places, with several vibrio from each, to see whether there are founder populations of vibrio from the water, or perhaps whether the bacteria spread with the cnidarians (co-evolution - parasite, pathogen, epiphyte...), etc.

So, all in all, an intriguing paper but frustratingly light on conclusions, and perhaps missing some important/helpful molecular phylogenetic data. Hopefully this will be filled in in future publications.