WWWD – What would Wolbachia do? Not always male destruction. Not always mutualism. Sometimes they disappear.

Interesting paper in Nature Genetics: Genomics of Loa loa, a Wolbachia-free filarial parasite of humans : Nature Genetics : Nature Publishing Group.  It is “Open” due to the NPG policy for papers reporting genome data.

Anyway – the paper deals in parts with the biology of the interaction between Wolbachia and filiarial nematodes.  Wolbachia are these fascinating intracellular bacteria that are found to infect a diversity of invertebrate species.  In 2004 we published the genome sequence of the first Wolbachia genome – a strain that infects Drosophila melanogaster and causes male specific detrimental effects (see summary here and our paper here and a general review here).  Many of the Wolbacia that are well studied have male specific effects leading us to jokingly call them “WMDs” the Wolbachia of male destruction.

Interestingly, Wolbachia also infect filarial nematodes, such as the ones that cause various nasty diseases.  And these Wolbachia not only do not have any obvious male specific detrimental effects, they appear to be mutualistic symbionts of the nematodes.  That is where this paper comes in.  The authors sequenced the genome of a filarial nematode that does not have any Wolbachia.  The premise here is – if Wolbachia are needed for other nematodes maybe one can figure out what Wolbachia do by identifying features in the Wolbachia-free nematode that are not in the ones with Wolbachia. 

They write

Loa loa, the African eyeworm, is a major filarial pathogen of humans. Unlike most filariae, L. loa does not contain the obligate intracellular Wolbachia endosymbiont. We describe the 91.4-Mb genome of L. loa and that of the related filarial parasite Wuchereria bancrofti and predict 14,907 L. loa genes on the basis of microfilarial RNA sequencing. By comparing these genomes to that of another filarial parasite, Brugia malayi, and to those of several other nematodes, we demonstrate synteny among filariae but not with nonparasitic nematodes. The L. loa genome encodes many immunologically relevant genes, as well as protein kinases targeted by drugs currently approved for use in humans. Despite lacking Wolbachia, L. loa shows no new metabolic synthesis or transport capabilities compared to other filariae. These results suggest that the role of Wolbachia in filarial biology is more subtle than previously thought and reveal marked differences between parasitic and nonparasitic nematodes.

Anyway – the paper is worth checking out.

Figure 3: Phylogenomic analysis of nematodes.. Maximum likelihood, parsimony and Bayesian methods all estimated an identical phylogeny using the concatenated protein sequences of 921 single-copy orthologs. To the left of each node are likelihood bootstrap support values/parsimony bootstrap support values/Bayesian posterior probabilities. The distributions of genes in the ortholog clusters are shown to the right of the phylogeny. Core genes are encoded by all genomes, shared genes are encoded by at least two but fewer than all genomes, and unique genes are found only in one genome. Orthologs specific to the nonparasitic (C. elegans, C. briggsae and P. pacificus) and filarial nematodes are also highlighted. Of the 6,280 L. loa genes with no functional assignment, 3,665 are unique to L. loa and 1,158 are filarial specific. From http://www.nature.com/ng/journal/vaop/ncurrent/full/ng.2585.html

Profile of Michael Turelli in the Sacramento Bee

Pretty good profile of Michael Turelli in the Sacramento Bee: UCD professor Michael Turelli finds biomathematics work ‘ridiculously satisfying’ – Living Here – The Sacramento Bee.  It discusses his career from PhD work to early research to his new work on Wolbachia.  Note of lack of objectivity on my part – Turelli was the first person to recruit me to UC Davis and, well, I love him.  He simply is great …

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.