AUTHOR=Alonso-Pernas Pol , Bartram Stefan , Arias-Cordero Erika M. , Novoselov Alexey L. , Halty-deLeon Lorena , Shao Yongqi , Boland Wilhelm 

TITLE=In Vivo Isotopic Labeling of Symbiotic Bacteria Involved in Cellulose Degradation and Nitrogen Recycling within the Gut of the Forest Cockchafer (Melolontha hippocastani)

JOURNAL=Frontiers in Microbiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2017.01970

DOI=10.3389/fmicb.2017.01970

ISSN=1664-302X

ABSTRACT=<p>The guts of insects harbor symbiotic bacterial communities. However, due to their complexity, it is challenging to relate a specific symbiotic phylotype to its corresponding function. In the present study, we focused on the forest cockchafer (<italic>Melolontha hippocastani</italic>), a phytophagous insect with a dual life cycle, consisting of a root-feeding larval stage and a leaf-feeding adult stage. By combining <italic>in vivo</italic> stable isotope probing (SIP) with <sup>13</sup>C cellulose and <sup>15</sup>N urea as trophic links, with Illumina MiSeq (Illumina-SIP), we unraveled bacterial networks processing recalcitrant dietary components and recycling nitrogenous waste. The bacterial communities behind these processes change between larval and adult stages. In <sup>13</sup>C cellulose-fed insects, the bacterial families Lachnospiraceae and Enterobacteriaceae were isotopically labeled in larvae and adults, respectively. In <sup>15</sup>N urea-fed insects, the genera <italic>Burkholderia</italic> and <italic>Parabacteroides</italic> were isotopically labeled in larvae and adults, respectively. Additionally, the PICRUSt-predicted metagenome suggested a possible ability to degrade hemicellulose and to produce amino acids of, respectively, <sup>13</sup>C cellulose- and <sup>15</sup>N urea labeled bacteria. The incorporation of <sup>15</sup>N from ingested urea back into the insect body was confirmed, in larvae and adults, by isotope ratio mass spectrometry (IRMS). Besides highlighting key bacterial symbionts of the gut of <italic>M. hippocastani</italic>, this study provides example on how Illumina-SIP with multiple trophic links can be used to target microorganisms embracing different roles within an environment.</p>