Viral communities in millipede guts: Insights into the diversity and potential role in modulating the microbiome.

Millipedes are important detritivores harbouring a diverse microbiome. Previous research focused on bacterial and archaeal diversity, while the virome remained neglected. We elucidated the DNA and RNA viral diversity in the hindguts of two model millipede species with distinct microbiomes: the tropical Epibolus pulchripes (methanogenic, dominated by Bacillota) and the temperate Glomeris connexa (non-methanogenic, dominated by Pseudomonadota). Based on metagenomic and metatranscriptomic assembled viral genomes, the viral communities differed markedly and preferentially infected the most abundant prokaryotic taxa. The majority of DNA viruses were Caudoviricetes (dsDNA), Cirlivirales (ssDNA) and Microviridae (ssDNA), while RNA viruses consisted of Leviviricetes (ssRNA), Potyviridae (ssRNA) and Eukaryotic viruses. A high abundance of subtypes I-C, I-B and II-C CRISPR-Cas systems was found, primarily from Pseudomonadota, Bacteroidota and Bacillota. In addition, auxiliary metabolic genes that modulate chitin degradation, vitamins and amino acid biosynthesis and sulphur metabolism were also detected. Lastly, we found low virus-to-microbe-ratios and a prevalence of lysogenic viruses, supporting a Piggyback-the-Winner dynamic in both hosts.

Functional similarity, despite taxonomical divergence in the millipede gut microbiota, points to a common trophic strategy.

BACKGROUND: Many arthropods rely on their gut microbiome to digest plant material, which is often low in nitrogen but high in complex polysaccharides. Detritivores, such as millipedes, live on a particularly poor diet, but the identity and nutritional contribution of their microbiome are largely unknown. In this study, the hindgut microbiota of the tropical millipede Epibolus pulchripes (large, methane emitting) and the temperate millipede Glomeris connexa (small, non-methane emitting), fed on an identical diet, were studied using comparative metagenomics and metatranscriptomics. RESULTS: The results showed that the microbial load in E. pulchripes is much higher and more diverse than in G. connexa. The microbial communities of the two species differed significantly, with Bacteroidota dominating the hindguts of E. pulchripes and Proteobacteria (Pseudomonadota) in G. connexa. Despite equal sequencing effort, de novo assembly and binning recovered 282 metagenome-assembled genomes (MAGs) from E. pulchripes and 33 from G. connexa, including 90 novel bacterial taxa (81 in E. pulchripes and 9 in G. connexa). However, despite this taxonomic divergence, most of the functions, including carbohydrate hydrolysis, sulfate reduction, and nitrogen cycling, were common to the two species. Members of the Bacteroidota (Bacteroidetes) were the primary agents of complex carbon degradation in E. pulchripes, while members of Proteobacteria dominated in G. connexa. Members of Desulfobacterota were the potential sulfate-reducing bacteria in E. pulchripes. The capacity for dissimilatory nitrate reduction was found in Actinobacteriota (E. pulchripes) and Proteobacteria (both species), but only Proteobacteria possessed the capacity for denitrification (both species). In contrast, some functions were only found in E. pulchripes. These include reductive acetogenesis, found in members of Desulfobacterota and Firmicutes (Bacillota) in E. pulchripes. Also, diazotrophs were only found in E. pulchripes, with a few members of the Firmicutes and Proteobacteria expressing the nifH gene. Interestingly, fungal-cell-wall-degrading glycoside hydrolases (GHs) were among the most abundant carbohydrate-active enzymes (CAZymes) expressed in both millipede species, suggesting that fungal biomass plays an important role in the millipede diet. CONCLUSIONS: Overall, these results provide detailed insights into the genomic capabilities of the microbial community in the hindgut of millipedes and shed light on the ecophysiology of these essential detritivores. Video Abstract.

Evaluation of physicochemical and antioxidant properties of two stingless bee honeys: a comparison with Apis mellifera honey from Nsukka, Nigeria.

OBJECTIVE: Several physical, biochemical and antioxidant properties of two Nigerian stingless bee honey varieties (Melipona sp. and Hypotrigona sp.) were compared with Apis mellifera honey using standard analytical procedures. RESULTS: The mean pH of Apis mellifera, Hypotrigona sp. and Melipona sp. honeys were 4.24 ± 0.28, 3.75 ± 0.11 and 4.21 ± 0.37 respectively. The mean moisture contents of the honeys were 11.74 ± 0.47, 17.50 ± 0.80, and 13.86 ± 1.06%. Honey samples from Hypotrigona sp. when compared with other honey samples had the highest mean total dissolved solids (370.01 ± 22.51 ppm), hydroxymethylfurfural (16.58 ± 0.37 mg/kg), total acidity (35.57 ± 0.42 meq/kg), protein content (16.58 ± 0.37 g/kg), phenol content (527.41 ± 3.60 mg/kg), and ascorbic acid (161.69 ± 6.70 mg/kg), antioxidant equivalent-ascorbic acid assay value (342.33 ± 0.78 mg/kg) as well as ferric reducing power (666.88 ± 1.73 µM Fe(II)/100 g) (p < 0.05). Several strong correlations were observed among some of the parameters of the honeys. This is the first study to compare the properties of Nigerian honey bees. Our results suggested that these honeys (specifically Hypotrigona sp. honey) is a good source of antioxidants comparable to A. mellifera honey.