Insect-bacterial symbiosis is a rapidly growing area of research.
Multicellular life forms (animals, plants, fungi, etc.) have evolved in many ways: one of these involves streamlining or losing capacities that may have been metabolically expensive and yet unnecessary. Heterotrophs feeding on other organisms might “cut corners” in life by dropping the ability to synthesize complex biological nutrients that can instead be obtained from their food.
In animals, this may have happened early, with the loss of ability to synthesize many amino acids and vitamins or cofactors, forming a set of “essential amino acids and vitamins” that must be obtained from their food.
What can animals do if they change to a diet depleted in these essential nutrients, e.g. a diet of sugary plant sap or vitamin-poor blood?
This is the problem facing the insect order Hemiptera. These bugs have piercing and sucking mouthparts that give them access to plant vascular tissue or host blood vessels, but limit them to the problems inherent in these liquid diets.
Solution: bacterial endosymbionts! Most Hemipteran insects obligately depend on one or more bacterial partners as nutritional symbionts. Amazingly, this solution to the problem has arisen repeatedly, with bacteria entering into symbiosis with these bugs repeatedly over evolutionary time. More amazing still, these bacteria often (more often than not) form cooperating pairs (or larger groups) to serve the nutritional supplementation needs of the host.
Currently, we are keenly interested in the symbionts of Membracids, Leafhoppers, and Planthoppers. Neotropical membracids have a rich array of uncharacterized endosymbionts in their bacteriomes. We are curious how these might interact with Hymenopteran (ant and bee) trophobionts that tend (protect) some species of membracid in exchange for their sugary honeydew. I was awarded funding with Dr. Mônica T. Pupo, University of São Paulo – Ribeirão Preto, Brazil through a FAPESP SPRINT Award, jointly funded by Brazil’s FAPESP and Texas Tech to collect and research these insects in Brazil. Several leafhoppers (e.g. Typhlocybinae) and planthoppers, appear to have lost their endosymbionts. We have been examining the genomic footprints and possible facilitating genes in these aposymbiotic representatives. We were previously interested in the invasive kudzu bug Megacopta cribraria and its bacterial partners Ishikawaella capsulata and Wolbachia. The genotype of Ishikawaella may determine the pest-status of the insect: whether it thrives on soybeans or its native legume, kudzu. We are also interested in the family Membracidae which host a number of bacterial and fungal symbionts. We use population genomics, comparative genomics, metagenomics, transcriptomics, and are working on proteomics and metabolomics approaches to understand how these insects can be so successful.
Our publications on this work:
2021 Salazar MM, Pupo MT, Brown AMV. Co-occurrence of viruses, plant pathogens, and symbionts in an underexplored hemipteran clade. Frontiers in Cellular and Infection Microbiology 11:715998. doi: 10.3389/fcimb.2021.715998 (an Invited Paper for Topic: Molecular and Cellular Interactions of Resident Symbionts and Transmitted Pathogens With Each Other and Their Arthropod Hosts)
2014 Brown AMV, Huynh LY, Bolender CM, Nelson KG, McCutcheon JP. Population genomics of a symbiont in the early stages of a pest invasion. (Invited original research article for Nature’s Microbiome). Molecular Ecology 23:1516-1530. doi: 10.1111/mec.12366
2014 Brown AMV. Microevolution of insect-bacterial mutualists: a population genomics perspective. In Evolutionary Biology: Genome Evolution, Speciation, Coevolution and Origin of Life. Pontarotti, P. (ed.). Springer International, Switzerland p. 247-259.
(Invited Talk) 2014 Brown AMV, Huynh LY, McCutcheon JP. Population genomic and transcriptomic insights into symbiont adaptation during a rapid insect invasion. Horizons in the Field of Symbiosis Member Symposium, Entomological Society of America Meetings, Nov 15-19, 2014, Portland, OR.