A Ta­ble for Two

by Elio

What fun, un­less you are the one be­ing preyed upon. Two preda­tors, a phage and a "bac­te­rio­phagous" bac­terium, si­mul­ta­ne­ously dine and re­pro­duce in one host cell.

Doesn't this open a whole lot of ques­tions, such as: How of­ten does co-in­fec­tion take place in the wild? Do the two preda­tors "talk" to each other? Does this mat­ter for the geo­chem­i­cal cy­cles? And, most im­por­tant, who has first dibs?

Huan Chen and Henry Williams of Florida A&M Uni­ver­sity ask just such ques­tions, us­ing the ma­rine bac­terium Vib­rio vul­nifi­cus as the prey, with both a phage and a BALO, Bdellovib­rio-like or­gan­ism (ac­tu­ally some­thing called Clus­ter IX of Bac­te­ri­ovo­rax) as preda­tors. They mixed the par­tic­i­pants in a predator/prey ra­tio of 1:1:1, let them work on each other, then looked at what was hap­pen­ing in thin sec­tions un­der the elec­tron mi­cro­scope. The con­clu­sion? The two preda­tors do not seem to com­pete with one an­other, rather they both feast on the prey to­gether. Both the in­vad­ing bac­terium and the phage mul­ti­ply within the same host cell. This is a first.

TEMs of thin sec­tions of in­fected V. vul­nifi­cus prey cells. (A) In­fected by phage only. (B) In­fected by BALO only. (C and D) Co-in­fec­tion by both BALO and phage. In (D) BALO did not change the shape of the prey cell. B, C, and D show the bdel­loplast, the post-BALO in­fec­tion struc­ture with the preda­tor re­sid­ing in­side the prey cell. Bar = 500 nm. Fron­tispiece: Scan­ning elec­tron mi­cro­graphs show­ing BALO cells and phages at­tached to a prey cell (A). Source

Bdellovib­rios and phages re­pro­duce by very dif­fer­ent mech­a­nisms, but both re­quire an in­tact host cell. Specif­i­cally, bdellovib­rios pen­e­trate the cell wall, re­side in the periplas­mic space, and shut off the host meta­bolic func­tions. They in­duce cell ly­sis af­ter about 15 min­utes, which is less than the time most phages re­quire for their cy­cle. But the phage, it ap­pears, is speedy enough to repli­cate in the time avail­able. No doubt, there are some com­plex dy­nam­ics afoot.

This is a com­pli­cated busi­ness. Whereas each of the two preda­tors has its own lifestyle with re­gards to cel­lu­lar lo­cal­iza­tion, re­pro­duc­tive strat­egy, and ki­net­ics, co-in­fec­tion makes spe­cial de­mands on each. Just how in­fec­tion by BALO af­fects that of the phage and vice versa re­mains a fer­tile topic for in­ves­ti­ga­tion. Who says that things are sim­ple in the oceans' mi­cro­biome? The au­thors point out: Rather than the viruses and Bdellovib­rio and like or­gan­isms com­pet­ing for a sin­gle prey cell, both can sur­vive in the same cell and suc­cess­fully re­pro­duce them­selves. This is an es­pe­cially valu­able mech­a­nism when the prey is in short sup­ply, and the sur­vival of the preda­tors may be at stake.

The au­gust (and rel­a­tively new) ASM jour­nal mBio pub­lished this work in a sec­tion en­ti­tled Ob­ser­va­tions. This is a nice in­no­va­tion for which the ed­i­tors should be saluted.