Enterobacter sp.: LPS and colonization in the gut of Anopheles gambiae

The mosquito gut accommodates a complex microbial community. Enterobacter sp. is an abundant bacterium in the blood fed gut. We have isolated Enterobacter sp. strain Ag1 from the gut of Anopheles gambiae G3 colony reared in the lab insectary. Our knowledge about how bacteria colonize the gut and form a stable microbial community is very limited. It is a fundamental aspect of the structure and function of the gut microbiome. To be able to study the genes involved in the gut colonization, we generated a mutant library of Enterobacter sp. utilizing the transposon mediated mutagenesis approach. One of mutants had the gene O-antigen ligase (waaL) disrupted. The mutant had defective LPS structure, demonstrated by LPS PAGE gel. The mutant (mt) and wild type (wt) showed similar growth pattern, but mt reduced tolerance to paraquat, a strong oxidative stress inducer, compared to the wild type (wt). To track the behavior of the wt and mt in the gut, we tagged wt and mt bacteria with GFP and RFP, respectively. After oral feeding the wt bacteria were able to stay in the sugar fed gut, and proliferate in the blood fed gut while the mt bacteria were not. Evidently the deficiency of LPS compromised the colonization ability. Additionally, when bacteria (wt and mt) ingested mosquitoes were infected with Plasmodium berghei, wt fed mosquitoes and control mosquitoes showed similar infection while the mt fed group had significant higher oocyst load. Mosquito immunity against P. berghei is largely controlled by Toll pathway. The effect of mt with defective LPS on the anti-P.berghei immunity triggered interest in potential roles that LPS may play in priming mosquito gut immunity.