Spider phylosymbiosis: divergence of widow spider species and their tissues' microbiomes.

BACKGROUND: Microbiomes can have profound impacts on host biology and evolution, but to date, remain vastly understudied in spiders despite their unique and diverse predatory adaptations. This study evaluates closely related species of spiders and their host-microbe relationships in the context of phylosymbiosis, an eco-evolutionary pattern where the microbial community profile parallels the phylogeny of closely related host species. Using 16S rRNA gene amplicon sequencing, we characterized the microbiomes of five species with known phylogenetic relationships from the family Theridiidae, including multiple closely related widow spiders (L. hesperus, L. mactans, L. geometricus, S. grossa, and P. tepidariorum). RESULTS: We compared whole animal and tissue-specific microbiomes (cephalothorax, fat bodies, venom glands, silk glands, and ovary) in the five species to better understand the relationship between spiders and their microbial symbionts. This showed a strong congruence of the microbiome beta-diversity of the whole spiders, cephalothorax, venom glands, and silk glands when compared to their host phylogeny. Our results support phylosymbiosis in these species and across their specialized tissues. The ovary tissue microbial dendrograms also parallel the widow phylogeny, suggesting vertical transfer of species-specific bacterial symbionts. By cross-validating with RNA sequencing data obtained from the venom glands, silk glands and ovaries of L. hesperus, L. geometricus, S. grossa, and P. tepidariorum we confirmed that several microbial symbionts of interest are viably active in the host. CONCLUSION: Together these results provide evidence that supports the importance of host-microbe interactions and the significant role microbial communities may play in the evolution and adaptation of their hosts.

Relationships between soil organic matter, nutrients, bacterial community structure, and the performance of microbial fuel cells.

Microbial fuel cells (MFCs) offer the potential for generating electricity, mitigating greenhouse gas emissions, and bioremediating pollutants through utilization of a plentiful renewable resource: soil organic carbon. We analyzed bacterial community structure, MFC performance, and soil characteristics in different microhabitats within MFCs constructed from agricultural or forest soils in order to determine how soil type and bacterial dynamics influence MFC performance. Our results indicated that MFCs constructed from agricultural soil had power output about 17 times that of forest soil-based MFCs and respiration rates about 10 times higher than forest soil MFCs. Agricultural soil MFCs had lower C:N ratios, polyphenol content, and acetate concentrations than forest soil MFCs. Bacterial community profile data indicate that the bacterial communities at the anode of the high power MFCs were less diverse than in low power MFCs and were dominated by Deltaproteobacteria, Geobacter, and to a lesser extent, Clostridia, while low-power MFC anode communities were dominated by Clostridia. These results suggest that the presence of organic carbon substrate (acetate) was not the major limiting factor in selecting for highly electrogenic bacterial communities, while the quality of available organic matter may have played a significant role in supporting high performing bacterial communities.