B. aphidicola is an endosymbiont of aphids (sap sucking insects). This bacterium lives in specialised cells called bacteriocytes and stablishes an symbiotic relationship with its host. They get shelter and food, and they provide aminoacids that are not found in the aphid’s strict diet.
That’s kind of the straightforward anwser to why the aphids harbor this guys. The interesting thing is that in some other cases the endosymbiont present in other insects don’t show a clear “function”. Basically, other antibiotic treated species of insects that have endosymbionts have been shown not to have any “visible” problem after the removal of them. For instance, this applies to Blochmania floridanus and its ant host Camponotus.
In a recent paper published in PLoS Biology Nancy Moran’s team found an unexpected “function” of Buchnera.
They found that some buchnera strains upregulate a heat-shock protein when exposure to 35C and some strains didn’t. The reason for that, is a single-point mutation in the promoter of the gene that encodes the heat-shock protein. The strains with the missing nucleotide didn’t upregulate the gene.
Here comes the good stuff: When they exposed two groups of juniles aphids (one with each strain) at 35C for four hours, few of the ones with the nucleotide missing strains could reproduce afterwards, whereas the others encountered no problem. Also the aphids bearing bacteria with short promoters weighed less as adults.
Even more interesting! strains from Arizona showed no mutations whereas strains from cooler areas had a third of the populations carrying the shorter promoters.
Might this confer advantage in cooler climates… YES!
They found that the opposite is true when the aphids are exposed at 15C.The aphids with Buchnera strains that carried the mutation produced progeny faster than the ones bearing strains with longer promoters.
That’s absolutely fantastic!
How can the upregulation of heat-shock genes affect so drastically (only four hours of exposure) the aphids?
This is a beautiful example of how the question is the most important part of the research, what do you call function (like in the case of Blochmania and Camponotus? what are the normal conditions?
How much left to be known. How much left to be known. I love it!!