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The Ironwood tree (Casuarina equisetifolia) holds a significant ecological role in Guam where a decline in Ironwood trees was first documented in 2002. Studies have linked the Ironwood tree decline (IWTD) to bacteria from the Ralstonia solanacearum complex and wetwood bacteria, specifically Klebsiella oxytoca and Klebsiella variicola. Presence of termites was first found to be associated with IWTD in 2010; however, the role of termites in IWTD is still not clear. The Asian subterranean termite, Coptotermes gestroi (Wasmann) (Blattodea: Rhinotermitidae) frequently attacks Ironwood trees. As workers of this soil-dwelling species of the lower termites harbor a diverse microbial community in their bodies, we examined whether C. gestroi workers carry IWTD-associated bacteria and could, therefore, act as vectors. We described the bacterial community in C. gestroi workers using 16S rRNA gene sequencing and tested the impact of factors related to the location and health of the Ironwood tree the termites were collected from on termite bacterial diversity. Feeding assays were performed to assess if workers show preference in consumption depending on the amount of Ralstonia and wetwood bacteria in the food source. Health of Ironwood trees and level of site management impacted the bacterial composition of C. gestroi termite workers attacking the trees. Although C. gestroi workers equally consumed food sources with high and low Ralstonia and wetwood bacteria load in lab experiments, Ralstonia and other IWTD-related bacteria were not detected in considerable amounts in termite workers collected from trees. Thus, C. gestroi workers are not a vector for bacteria associated with IWTD in Guam.

Ironwood trees (Casuarina equisetifolia) in Guam have been suffering from Ironwood Tree Decline (IWTD) since 2002. Putative plant pathogenic bacteria such as Ralstonia solanacearum and Klebsiella species were identified in the ooze of declining trees and considered to be linked to IWTD. In addition, termites were found to be significantly associated with IWTD. Microcerotermes crassus Snyder (Blattodea: Termitidae) was identified as a termite species that attacks ironwood trees in Guam. Since termites harbor a diverse community of symbiotic and environmental bacteria, we sequenced the microbiome of M. crassus workers attacking ironwood trees in Guam to assess the presence of IWTD-associated pathogens in termite bodies. This dataset contains 652,571 raw sequencing reads present in M. crassus worker samples collected from six ironwood trees in Guam obtained via sequencing the V4 region of the16S rRNA gene on the Illumina NovaSeq (2 × 250bp) platform. Sequences were taxonomically assigned in QIIME2 using SILVA 132 and NCBI GenBank as reference databases. Spirochaetes and Fibrobacteres were the most dominant phyla in M. crassus workers. No putative plant pathogens of the genera Ralstonia or Klebsiella were found in the M. crassus samples. The dataset has been made publicly available through NCBI GenBank under BioProject ID PRJNA883256. This dataset can be used to compare the bacterial taxa present in M. crassus workers in Guam to bacteria communities of related termite species from other geographical locations. In addition, this dataset can also be used to investigate the relationship between termite microbiomes and the microbiomes of ironwood trees they attack and of the surrounding soil.