Talmudic Question #94

by Mark Martin

Bacterial bioluminescence is ubiquitous in marine environments, both among free living and mutualistic microbes. Why is this phenotype comparatively rare in terrestrial and freshwater environments (the fascinating Photorhabdus being a notable exception)?

Comments

[mark martin]

Mark Martin replies to Nathan Myers:

Interesting question from Nathan Myers. There are a few species of truly marine (as opposed to estuarine insects). The question of why insects are so prevalent on land but rare in the ocean is an interesting one. Here is one overview:

http://thedragonflywoman.com/2012/05/25/marine-insects/

The author presents five solid considerations. Interesting thinking!

As for the prevalence of luminous marine bacteria, and their comparative rarity in terrestrial and freshwater environment continues to vex me!"

And it does!

Best,

MM

[Nathan Myers]

Are insects small enough to allow discussion here of why their habitat so precisely complements that of luminescent bacteria? (I doubt that the presence of the latter confines the former to fresh water.) Rivers must wash untold billions of insects out to sea, where they seem to expire without issue. Why this systematic failure to colonize?

[barrys]

answer in jest: no glowing bacteria in fresh water because the aquatic insects (which are mostly lacking in the oceans) find them and eat them.

[Mark O. Martin]

I thank Mehmet Berkmen for his comment. But is the ocean truly a homogenous environment? And if so, is it more homogenous than lakes? No freshwater luminous bacteria there.

As for caves...any luminous bacteria there? Not yet. And I would emphasize that I am discussing bacterial bioluminescence.

Here is the thing. Someone with mad bioinformatics skillz could easily check this out. Again: look at metagenomic data from the ocean, from freshwater, from the soil, etc. Scan for the presence of luxAB genes (which are highly conserved in bacteria that produce light). Do you find those genes in the "ocean" data? I sure hope so. Is there a way to detect frequency of occurrence. Almost certainly, given (again) those mad skillz I lack. Then ask the same question for the other metagenomic data sets. Fascinating!

I suspect that lux genes serve some other function that simply producing light. One such idea was tested and discussed here, on STC (http://schaechter.asmblog.org/schaechter/2006/12/an_iluminating_.html). It doesn't seem to be the case.

So the mystery continues! And I would LOVE to learn how to do that analysis I describe above, for any reader who does have the skill set, and doesn't mind teaching this aging canine some new prestidigitation!

[Mark O. Martin]

Well, I won't compete with Elio in the pun department (I realized in a flash of brilliance). But Jbitoun describes something interesting. There are a number of terrestrial fungi that are luminescent (http://www.livescience.com/2759-freaky-fungi-glow-dark.html). And many of the "glow in the dark" chemicals we have in household items become "charged up" in light and deliver it back in darkness for a short time.

But I continue to believe that there are always more mysteries to investigate. Especially microbial ones!

[Mehmet Berkmen]

The ocean can be viewed as a confluent, unhindered, homogenous environment where a light ray can travel without being blocked by trees, objects, rocks, etc...Since most microbes live on solid surface, any light produced is likely blocked by their environment and not be of use. If we assume that most microbes live in the soil, production of light becomes illogical. Caves are a good exception, with constant darkness, little soil and 360 degrees of solid surface for the microbes, and guess what? Caves are full of light producing organisms.

Simple no?

[Jbitoun]

Funny you should pose this question. Just last night after taking my dog outside, i noticed a luminescent stain on my doormat. I went inside to get an applicator to culture the stain but then it was gone! oh the Gods and their temporal nature :)

[Mark O. Martin]

Thanks to Elio for posting this TQ, which has long, long made me scratch my head!

Barry, bacterial bioluminescence is very common in the ocean, and extremely so among free-living bacteria as well as the fascinating symbionts you mention. I doubt that boron-containing AI are part of this conundrum (though who knows what BB will discover next!). I mean, many luminous marine bacteria live in the gut! I sometimes think, maybe such gut mutualists create (forgive me) glowing fish poop, that would be eaten by other fish (and thus spread the luminous bacteria to a new location). But bacterial bioluminescence is awfully widespread for that to be a reasonable explanation...

This always seemed like a great "quick topic" for a bioinformatician: look at metagenomic libraries from marine and freshwater samples. Look for prevalence of luxAB genes and close homologues. Maybe we are missing many, many freshwater and terrestrial luminous bacteria (perhaps they are quite dim, or luciferase serves a biochemical function other than light production; as I suspect) Wish I had the skillz to find out!

Elio adds:
Thanks for the thougthful response. It illuminates the subject!

[barry]

that is odd. the two examples i know about: hawaiin bobtail squid and deep sea fishes are in very DIFFERENT marine environments!

i recall a lecture by bonnie bassler on her shrimp and the quorum sensing had to do with boron containing molecules. that have anything to do with it?

a puzzler!