RachelM

If you’re going to cheat, you have to do it right. Cheating is a problem for any social system, Velicer explains in his article “Developmental cheating in the social bacterium Myxococcus xanthus.” Cheating isn’t something new to just bacteria. Ectomycorrhizal fungi, for example, assist trees in nutrient uptake but often “cheaters” or saprotrophic fungi take advantage of the relationship (Mayor, Elucidating the nutritional dynamics of fungi using stable isotopes 2008). Likewise, lightening bugs fluoresce in such a way to attract a female. Some lightening bugs take advantage of this signal and flash a deceptive signal. The male, thinking he has attracted the eye of a female, is led into a trap and eaten by the predator species.
M. xanthus is a type of microbe that lives in soil and exhibits both adventurous and social behavior. Social behavior involves cooperative behavior among the clones and while some may not win out in the end, they aid in the common good. In this case, being the only cheater in a band of cooperators seems to be the way to go.
Six strains originated from the original ancestor, DK1622. The strains were evolved for 1,000 generations from the original where the microbe was unable to exhibit social behavior. The ability to sporulate and its efficiency in sporulation then reflects its ability to potentially cheat.
H1 states that “defective strain may sporulate with the same efficiency as it does in the pure culture” and H2 states that “an evolved clone behaves as would a neutrally marked variant of the wildtype.” In both cases, the null hypothesis is rejected. Three cheaters appeared, GVB2063, GVB2083, and GVB143. When the evolved clones were mixed at low concentrations with the wildtype, they fared better than expected than on pure agar, where they exhibited defects in sporulation. As the mixing ratio went up, and the cheaters became more common, the sporulation efficiency went down. Also, cheaters that are not as “bad” as other cheaters tended to have more success at higher mixing ratios than those that were obligate cheaters. Being a cheater is effective but it also has some cost since cheaters harm the whole.
This experiment ultimately tested to see if variability amongst colonies could exist and if cheaters would contribute to the population. Velicer argues that, through this research, M. xanthus probably does has a low subpopulation of known cheaters in vivo.
I am most interested in the way in which this microbe might try to combat the cheaters. What kind of “policing mechanisms” would prevent cheaters from entering into a population? Furthermore, how can a reproductive cycle be unfavorable to a cheater? Can the bacteria develop some sort of allopathic technique to dissuade a strain so similar to their own? Velicer only mentions these techniques but does not go into detail. What kind of genotype would a wildtype strain have to have in order to repress these known cheaters? However, at the same time, would it be worth the extra effort to repress a subpopulation that does not threaten to take over the population? Basically, is it worth it to throw a microbe out of your game just because they don’t play nice?