Bac­terial In­di­vidu­al­ism: A Sur­vival Strategy for Hard Times

Whether you are a hu­man or a bac­terium, your en­vir­on­ment de­term­ines how you can de­velop. In par­tic­u­lar, there are two fun­da­mental prob­lems. First: what re­sources can you draw on to sur­vive and grow? And second: how do you re­spond if your en­vir­on­ment sud­denly changes?
A group of re­search­ers from Eawag, ETH Zurich, EPFL Lausanne, and the Max Planck In­sti­tute for Mar­ine Mi­cro­bi­o­logy in Bre­men re­cently dis­covered that the num­ber of in­di­vidu­al­ists in a bac­terial pop­u­la­tion goes up when its food source is re­stric­ted. Their find­ing goes against the pre­vail­ing wis­dom that bac­terial pop­u­la­tions merely re­spond, in hind­sight, to the en­vir­on­mental con­di­tions they ex­per­i­ence. In­di­vidu­al­ists, the study finds, are able to pre­pare them­selves for such changes well in ad­vance.

In a re­cent pa­per in the journal Nature Microbiology, re­search­ers work­ing with Frank Schreiber have shown that in­di­vidual cells in bac­terial pop­u­la­tions can dif­fer widely in how they re­spond to a lack of nu­tri­ents. Al­though all of the cells in a group are ge­net­ic­ally identical, the way they pro­cess nu­tri­ents from their sur­round­ings can vary from one cell to an­other. For ex­ample, bac­teria called Klebsiella oxytoca pref­er­en­tially take up ni­tro­gen from am­monium (NH4+), as this re­quires re­l­at­ively little en­ergy. When there is­n’t enough am­monium for the en­tire pop­u­la­tion, some of the bac­teria start to take up ni­tro­gen by fix­ing it from ele­ment­ary ni­tro­gen (N2), even though this re­quires more en­ergy. If the am­monium sud­denly runs out al­to­gether, these cells at least are pre­pared. While some cells suf­fer, the group as a whole can con­tinue to grow. “Al­though all of the bac­teria in the group are ge­net­ic­ally identical and ex­posed to the same en­vir­on­mental con­di­tions, the in­di­vidual cells dif­fer among them­selves,” says Schreiber.

Detailed insights thanks to the latest technology

Schreiber and his col­leagues were only able to re­veal the as­ton­ish­ing dif­fer­ences between the bac­teria by study­ing them very closely. “We had to meas­ure nu­tri­ent up­take by in­di­vidual bac­terial cells – even though these are only 2 μm large,” ex­plains Schreiber. “Usu­ally, mi­cro­bi­o­lo­gists study the col­lect­ive prop­er­ties of mil­lions or even bil­lions of bac­teria. It was only thanks to the close col­lab­or­a­tion between the re­search groups, and by pool­ing our ex­pert­ise and tech­nical equip­ment, that we were able to study the bac­teria in such de­tail.”

Bacteria are individualists, too

The present study shows to what ex­tent in­di­vidu­al­ity – in bac­teria and in gen­eral – can be es­sen­tial in a chan­ging en­vir­on­ment. Dif­fer­ences between in­di­vidu­als give the group new prop­er­ties, en­abling it to deal with tough en­vir­on­mental con­di­tions. “This in­dic­ates that bio­lo­gical di­versity does not only mat­ter in terms of the di­versity of plant and an­imal spe­cies but also at the level of in­di­vidu­als within a spe­cies,” says Schreiber.
Next, Schreiber and his col­leagues plan to study whether the in­di­vidu­al­istic be­ha­vior of spe­cific in­di­vidu­als is of equal im­port­ance in nat­ural en­vir­on­ments.