Microbes are very primitive – everyone knows that. However, their communities have managed to survive through millions of years and are very resistant to environmental changes. Microbial cultures are tough, but how do they achieve that being so primitive? Scientists from UCL and the University of Bath found that microbes actually vary their contribution to the common good to maximize the outcome.
This is one of the fundamental questions in biology – why individuals are contributing instead of exploiting contributions of others? How do they determine that it is better to work for a common good? Scientists have noticed that when microbes are in groups constituting their relatives, they contribute heavily, but when their surrounding individuals are unrelated they tend to exploit contributions of others. This is very interesting, because for the longest time scientists have wondered why cheaters do not make communities collapse and how do they maintain the cooperative system.
Not all microbes are social. That is why scientists decided to study the social amoeba Dictyostelium discoideum or slime mould. These amoebas live as individuals in soil, but come together to form slug-like creatures when food is scarce. This structure eventually becomes a fruiting body, but for this to happen all individuals have to cooperate. Amoebas in this bizarre structure can become stems or spores, only the latter being able to reproduce. Scientists wanted to see what makes individuals sacrifice themselves for the common good and found that microbes are actually quite savvy – they try to maximize their outcome. The best choice is to cheat, if you can get away with it. But if that compromises the group, you should cooperate, because then you are risking your own survival. It is remarkable that amoebas seem to consider the outcome.
Microbes vary their behaviour to maximise their profit – they are pretty much savvy investors rather than cheaters or co-operators. Author Professor Jason Wolf compared them to actual businessmen – the one having 80 % of the share will have to invest more than the one having 20 %. He said: “microbes with one genotype invest more resources in making the stalk if most of the others in the group share the same genes. If they don’t invest, they have more to lose because their stake is larger. Microbes of a minority genotype have less to lose if the fruiting body fails so go for maximum return by forming spores”.
If there was no balance between cooperation and cheating, the slug-like structure collapsed while trying form a fruiting body. So the group’s success depends, quite literally, on investing skills of individuals amoebas.