The Bacteria of a Fig Microcommunity
Authors: Woodruff Gavin C. , Moser Kimberly A. , Wang John 
Published: November 2024

Understanding the biotic drivers of diversity is a major goal of microbial ecology. One approach towards tackling this issue is to interrogate relatively simple communities that are easy to observe and perturb. Figs (syconia) of the genusFicusrepresent such a system. Here, we describe the microbial communities ofFicus septicafigs, which are associated with the nematodeCaenorhabditis inopinata(the sister species of theC. elegansgenetic model system). In 2019, 38Ficus septicafigs (across 12 plants in Taiwan) were dissected, and metadata such as foundress wasp number and nematode occupancy were collected for each fig. Suspensions derived from interior fig material and fig surface washes were prepared for 16S microbial metabarcoding. Over 3,000 OTUs were detected, and microbial communities were dominated by members ofProteobacteria,Bacteroidota, andActinobacteriota. Although microbial communities of fig exteriors and interiors can be distinguished, levels of microbial alpha diversity were comparable across these areas of the fig. Nematodes likewise had no detectable impact on microbial alpha diversity, although nematodes were associated with a modest change in microbial community composition. A handful of OTUs (associated with the generaKosokonia,Ochobactrum, andStenotrophomonas) revealed potential differential abundance among figs varying in nematode occupancy. Additionally, foundress wasp number was negatively correlated with microbial alpha diversity. These findings set the stage for future studies that directly test the role of nematode and wasp occupancy on microbial communities, as well as investigations that probe nematode-microbe interactions through laboratory experiments. Taken together, these results constitute a fundamental step in characterizing the natural microbial communities of figs andCaenorhabditisnematodes.

Importance

Unraveling why different species live in different places is a longstanding open question in ecology, and it is clear that interspecific interactions among species are a major contributor to species distributions.Ficusfigs are a useful system for ecological studies because they are relatively simple microcosms where characterizing animal community composition of multiple samples is straightforward. Additionally,Caenorhabditis inopinata, a close relative of theC. elegansgenetic model system, thrives inFicus septicafigs. Here, we tie 16S microbial metabarcoding to nematode and wasp occupancy data to understand the causes of bacterial community composition inF. septicafigs. We found that microbial composition, but not total diversity, varies among fig surface and interiors. Likewise, we found that nematode occupancy impacts microbial composition but not alpha diversity. Moreover, we show that as the number of foundress wasps increases, the microbial alpha diversity decreases. Finally, we identified OTUs that are potentially associated with nematode occupancy. Taken together, these results represent a key step in describing a microcommunity wherein ecological genetic hypotheses can be tested, as well as one that can potentially reveal the roles of uncharacterized genes in established model systems.