This action funds Matan Shelomi of the University of California, Davis, to conduct a research project, entitled "Gut Microbial Communities of the Stick Insects," during the summer of 2012 at Academia Sinica in Taipei, Tawian. The host scientist is Dr. Chih-Horng Kuo.
The Intellectual Merit of the research project is that it provides the first look at the digestive microbes of the walking sticks (Phasmatodea), an understudied order of which almost nothing is known about their digestive system. What little we do know suggests that the gut must contain some unique and so-far unknown adaptations for the grinding and digestion of the insects' leafy diets, for they do not have the same grinding organs as their relatives, the grasshoppers, or fermentation chambers like termites and roaches. The research investigates that the phasmid gut contains a complex microbial community that may contain symbionts with a digestive function, such as cellulose breakdown. During the course of this project, walking stick guts, diet, and wastes are being analyzed with modern, molecular techniques to identify all bacteria in the samples, their sources, and relative abundance, with the goal of helping understand how the insect is able to survive on its leafy diet. The data not only is of interest to biologists, but also to the biofuel industry, for the challenges these insects must overcome are the same as those that industry has been dealing with in trying to efficiently break down cellulosic matter.
Broader Impacts of an EAPSI fellowship include providing the Fellow a first-hand research experience outside the U.S.; an introduction to the science, science policy, and scientific infrastructure of the respective location; and an orientation to the society, culture and language. These activities meet the NSF goal to educate for international collaborations early in the career of its scientists, engineers, and educators, thus ensuring a globally aware U.S. scientific workforce.
In 2012, I mailed samples of stick insect (phasmid) guts and organs to a collaborating lab in Taiwan, where I was a guest scientist over the summer. Our goals were to perform high-throughput genetic sequencing to identify all of bacteria in the samples, using the latest and most powerful methods available. Because 99% of bacteria cannot be cultured in a lab, only such sequencing techniques can give you the best picture of both the bacterial diversity and relative abundance within a community. Walking sticks were chosen as the subject insect because 1) Nobody has looked at their microbial community before. 2) Their gut physiology is unique among the insects with some unusual structures that may have microbe-related functions. 3) My past research has shown that the phasmids can make their own digestive enzymes, which would reduce the need for microbial symbionts. I needed to check for sure whether phasmids have bacterial symbionts or not. The results of the experiment showed that phasmids do not seem to harbor symbionts. No bacteria (with one exception I'll get to later) appeared in any significant numbers. No similarities were found within single species or within gut sections within an individual. In short, phasmid digestion is symbiont-independent. That matches my previous research's hypotheses, but it is still surprising given the ubiquity of microbe-aided digestion in the insect world. This opens up a whole new field of inquiry into the digestive behaviors of herbivores. While no new bacteria were found, the promise of new enzymes that may have industrial or bioenergy uses has increased. The enzymatic potential of these insects is considerable. The one bacteria we did see in large numbers is Spiroplasma, which has no digestive role. Instead, it is an insect pathogenic bacteria that causes males to die and all eggs to become female. While this sounds like it would cause eventual population collapse, many walking sticks manage just fine with only females, cloning themselves and reproducing without sex. The species I found the Spiroplasma in is known to be occasionally parthenogenetic (only female), as was the case for my lab culture, but nobody had posited why that happens. Perhaps the Spiroplasma infection causes this. More research using other partheogenetic strains is needed. Beyond the science, this summer marked the forging of a new collaboration between my lab in the US and my host lab in Taiwan. The dividends this collaboration may pay in the future are unknown. My understanding of Asian research culture has increased, as has the strength of US-Taiwan ties through the many students on the East Asia and Pacific Summer Institutes Fellowship. I also assisted undergraduates in the Taiwanese lab with writing in English and finding potential labs to work for in the United States. The research is being written up into a paper, as well as conference and symposium presentations.
