A Snip­pet: Oceanic Con­ver­sa­tions

by Elio

In the ocean, bac­te­ria and eu­kary­otic mi­crobes (mainly the phy­to­plank­ton) in­ter­act in va­rious ways, some mu­tu­ally ben­e­fi­cial, oth­ers detri­men­tal. Many, per­haps most of these in­teractions, take place via chem­i­cal com­mu­ni­ca­tions. If you had a hy­dro phone-like gad­get that could de­tect chem­i­cals in­stead of sound, the racket would be deaf­en­ing. Yet, we know lit­tle about these go­ings-on. A re­cent pa­per lis­tens in on the con­ver­sa­tion be­tween Emil­iana hux­leyi or Ehux, a coc­col­ithophore mi­croalga that is one of the most abun­dant mem­bers of the phy­to­plank­ton, and a bac­terium of the genus Pseudoal­teromonas, which is also plenti­ful. These bac­te­ria are known to make com­po­nents that kill di­atoms and di­nofla­gel­lates, and are all found to­gether in the wa­ter col­umn. In ad­di­tion, Pseudoal­teromonas haloplank­tis is strongly at­tracted to an os­mo­pro­tec­tant, di­methyl­sul­fo­nio­pro­pi­onate, which is made in large amounts by EHUX. It bears men­tion­ing that Ehux is one of the most abun­dant eukar­yo­tic mi­crobes on earth, ca­pa­ble of mak­ing blooms in the ocean that can read­ily be seen from outer space.

Fig­ure 1. EHUX bloom from space (the coast off the south­west­ern tip of Eng­land) and un­der the scan­ning EM. Source

Ac­cord­ing to a re­cent pa­per, Pseudoal­teromonas pis­ci­cida makes a quo­rum-sens­ing mol­e­cule, 2‑hep­tyl-4-quinolone (HHQ), one of a fam­ily of such com­pounds that have been well char­ac­ter­ized as the Pseudomonas quinolone sig­nals. In fact, what makes this com­pound par­tic­u­larly in­ter­est­ing is that it dou­bles up as an an­tibi­otic and kills Ehux in cul­ture in the nanomo­lar range. Some chloro­phytes and di­atoms that are also mem­bers of the phy­to­plank­ton are not so af­fected. Killing of Ehux by HHQ is slow, sug­gest­ing that some­thing other than ly­sis may be in­volved. The au­thors found some other as yet uniden­ti­fied mol­e­cules caused im­me­di­ate ly­sis, so a col­lec­tion of com­pounds ap­pears to be in­volved. In­terestingly, HHQ has been pre­vi­ously found to be ac­tive against yeast as well as other bac­te­ria. In other words, this is a poly­glot term that can be un­der­stood by the users of dif­fer­ent lan­guages, both prokary­otic and eu­kary­otic. In­terk­ing­dom com­mu­ni­ca­tion via bac­te­r­ial quo­rum sens­ing mol­e­cules has been known be­fore, e.g., for com­mu­ni­cat­ing with hu­man stem cells. It makes you won­der how many such mul­ti­lin­gual sig­nals are out there.