Does Mother Provide? Re-Examination of Maternal and Embryonic Microbiomes of Diploptera punctata

The cockroach endosymbiont Blattabacterium cuenotii plays a central role in host nutrition throughout development, particularly during embryogenesis in the viviparous cockroach Diploptera punctata. However, the presence and potential functional relevance of non-blattabacterial taxa in developing embryos of this species remain unclear. Previous studies of maternal and embryonic microbiomes in D. punctata, based on Illumina 16S rRNA sequencing, have yielded inconsistent findings, partly due to differences in how endosymbiotic sequences were treated. Here, we reanalyzed microbiome data from two studies, with and without Blattabacterial reads, to reevaluate the presence and composition of non-blattabacterial taxa in embryonic microbiomes. Embryonic microbial communities (1) differed significantly from each other between datasets and (2) from associated maternal gut communities, suggesting that environmental (maternal, dietary, and laboratory) and sequencing factors may influence their acquisition and composition rather than reflecting a stable, consistently transmitted microbiome. Nevertheless, the detection of non-blattabacterial taxa in embryonic microbiomes suggests the possible acquisition of non-endosymbiotic bacteria by developing embryos. The functions of these microbes are speculated, but were not explicitly tested in this study and remain to be verified. Overall, our findings suggest that although non-endosymbiotic embryonic bacteria may be environmentally acquired and variable, their biological relevance remains unresolved and cannot be determined from 16S amplicon data alone. This highlights the importance of investigating acquired non-endosymbiotic bacteria and their potential functional roles in the development of viviparous cockroaches.