Open Access Biology highlights - The Intriguing Life of Endosymbionts

Two new articles published in the last issue of PLoS Biology bring forth some wildly interesting details about the lives of endosymbiotic bacteria.

One of the articles is about the role Wolbachia may play in speciation in Drosophila species. Wolbachia are a type of bacteira that are found to infect a wide diversity of invertebrate species. These bacteria are transmitted directly from mother to offspring much like mitochondria. Interestingly, many have evolved specialized means of negatively impacting male offspring. In the PLoS Biology study, the researchers were working on a type of Wolbachia known to cause cytoplasmic incompatability in which infected male offspring cannot produce offspring with uninfected females. Since these males can produce offspring with infected females, this helps contribute to the spread of the Wolbachia in the population. To make a long story short, the current paper proposes that not only can Wolbachia apparently lead to speciation through behavioral affects on the host, but that these affects can be stimulated even in species not infected by Wolbachia, if another similar species in the same area is infected. To learn more about the study read the synopsis here. I am personally interested in this story because we published the first Wolbachia genome a few years ago in PLoS Biology.

The second story to me is even more interesting. This relates to a bacterial symbiont that is found in the gut of a stinkbug species. The paper is important because the symbiont in this case does not live inside the cells of its host as do many other gut symbionts of insects. Instead, the symbiont lives in an extracellular capsule. Interestingly, the symbiont is transmitted to offspring not directly in eggs as in many other symbionts, but indirectly. The mother deposits a mass of the bacteria near the eggs and these are then consumed by the young just after hatching (the video of this is amazing).

The paper shows that these symbionts possess many of the genomic features found in other transmissable symbionts - including small genomes, high AT contents, and high rates of evolution (you can read more about this in my recent paper on symbionts of the glassy winged sharpshooter here or in my earlier blog). Many previously thought that these genomic features were related to the intracellular lifestyle of symbionts. But given that the same features are found in these extracellular symbionts, this suggests that the shared genome features are probably related to experiencing population bottlenecks in transmission from mother to offspring. See the synopsis of the paper here.