Prokaryotic communities play key roles in biogeochemical transformation and cycling of nutrients in the productive mangrove ecosystem. In this study, the vertical distribution of rhizosphere bacteria was evaluated by profiling the bacterial diversity and community structure in the rhizospheres of four mangrove species (Sonneratia alba, Rhizophora mucronata, Ceriops tagal and Avicennia marina) from Mida Creek and Gazi Bay, Kenya, using DNA-metabarcoding. Alpha diversity was not significantly different between sites, but, significantly higher in the rhizospheres of S. alba and R. mucronata in Gazi Bay than in Mida Creek. Chemical parameters of the mangrove sediments significantly correlated inversely with alpha diversity metrics. The bacterial community structure was significantly differentiated by geographical location, mangrove species and sampling depth, however, differences in mangrove species and sediment chemical parameters explained more the variation in bacterial community structure. Proteobacteria (mainly Deltaproteobacteria and Gammaproteobacteria) was the dominant phylum while the families Desulfobacteraceae, Pirellulaceae and Syntrophobacteraceae were dominant in both study sites and across all mangrove species. Constrained redundancy analysis indicated that calcium, potassium, magnesium, electrical conductivity, pH, nitrogen, sodium, carbon and salinity contributed significantly to the species–environment relationship. Predicted functional profiling using PICRUSt2 revealed that pathways for sulfur and carbon metabolism were significantly enriched in Gazi Bay than Mida Creek. Overall, the results indicate that bacterial community composition and their potential function are influenced by mangrove species and a fluctuating influx of nutrients in the mangrove ecosystems of Gazi Bay and Mida Creek.

Microbiota of termites is crucial for nitrogen cycle activities and degradation of recalcitrant components of plant biomass that influence soil structure and carbon mineralization in tropical and subtropical regions. The aim of this study was to isolate and characterize gut bacteria that may be potentially associated with nitrogen metabolism from two fungus-feeding termites (Macrotermes and Odontotermes spp.). Twenty termites from the intact colony of each termite species were aseptically degutted. Gut homogenate was inoculated and cultured on selective media for the isolation of pure bacteria. Pure bacterial isolates were characterized using their morphological, biochemical and molecular characters. DNA was extracted from the isolates, polymerase chain reaction (PCR) amplified and sequenced. The 16S rDNA gene sequences were blastn analyzed against the Genbank database and phylogenetic analysis was performed using MEGA 5 software. All forty-six isolates reacted positive for the ammonifying, nitrate, catalase and nitrogenase tests. Phylogenetic analysis grouped the isolates into three phyla: Firmicutes, Proteobacteria and Actinobacteria. Isolates were affiliated with the genera Pseudomonas, Citrobacter, Enterobacter, Proteus, Klebssiella, Bacillus, Staphylococcus, Rhodococcus and Micrococcus. The results confirm that termites harbor diverse gut bacterial groups that have different physiological/enzymatic activities and might have functional implications in the termitemicrobe symbiotic association.

The fungus-cultivating termites (Macrotermitinae) form part of diverse termite fauna in Africa, but information on their fungal symbionts is inadequate and poorly understood. In this study, the fungal communities and structure between termite gut, mound and surrounding soil were determined using the 454 pyrosequencing-based analysis of the internal transcribed spacer (ITS) gene sequences. Genomic DNA was extracted and purified from the guts of three termites (Odontotermes sp., Macrotermes michaelseni and Microtermes sp.), mound and surrounding soil samples for highthroughput sequencing. A total of 15,256 sequences were obtained and individual samples contained between 4 and 133 operational taxonomic units (OTUs). Termite gut had the least fungal diversity, dominated by members of the Basidiomycota (> 98%). More than 98% of the gut sequences were of the genus Termitomyces, while < 2% were related to the genera Chaetomium, Fusarium, Eupenicillium, Cladosporium, Curreya and Phaeosphaeria with between 95 and 98% pair-wise sequence identities. Members of Ascomycota (> 94%) were the most abundant in the mound and soil, but significantly differed (P value of 0.04; R value = 0.909) between the mound and soil environments. The results confirm that the genus Termitomyces exist in a tight association with their hosts and that Termitomyces species are scarcely present in the mound and soil. In addition, by altering soil properties; the fungus-cultivating termites modify the fungal community composition and structure in the mound and surrounding soil environments.

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