ABSTRACT
The common bean (Phaseolus vulgaris L.) is a yearly herbaceous plant grown for its edible dry seeds. Despite that, pests and diseases have contributed to the decline of common bean production in Kenya. Therefore, the study aimed to identify bacteria from Lake Bogoria, assess the pathogenicity of Rhizoctonia solani Kühn, screen for effective antifungal agents, and determine secondary metabolites for the biocontrol of R. solani. A total of 49 bacteria were isolated, of which 10 isolates had varied mycelial inhibition rates of R. solani in the co-culture technique. The efficacy of volatile compounds of the three selected bacterial strains had varied mycelial growth and percent reduction against R. solani. The pathogenicity assay showed varied plant parameters and biomass of R. solani on common bean plantlets. The molecular characterization based on 16 S ribosomal RNA confirmed the selected bacterial strains' identity with a diversity similar to the Bacillus genus. Gas chromatography-mass spectrometry analysis of secondary metabolites showed different antimicrobial compounds produced by Bacillus subtilis strain TW21. In conclusion, Lake Bogoria harbors useful microbes as biocontrol agents against plant pathogens. The current study discovers the potential biocontrol bacteria isolates from Lake Bogoria as alternative bioagents against R. solani. Therefore, the isolate Bacillus subtilis strain TW21 can be assessed further for toxicological and ecotoxicological studies and registered by the Pest Control Products Board (PCPB), Kenya, as a biocontrol product against common diseases affecting common beans' production.
ABSTRACT
The obstacle to optimal utilization of biogas technology is poor understanding of biogas microbiomes diversities over a wide geographical coverage. We performed random shotgun sequencing on twelve environmental samples. Randomized complete block design was utilized to assign the twelve treatments to four blocks, within eastern and central regions of Kenya. We obtained 42 million paired-end reads that were annotated against sixteen reference databases using two ENVO ontologies, prior to ß-diversity studies. We identified 37 phyla, 65 classes and 132 orders. Bacteria dominated and comprised 28 phyla, 42 classes and 92 orders, conveying substrate's versatility in the treatments. Though, Fungi and Archaea comprised 5 phyla, the Fungi were richer; suggesting the importance of hydrolysis and fermentation in biogas production. High ß-diversity within the taxa was largely linked to communities' metabolic capabilities. Clostridiales and Bacteroidales, the most prevalent guilds, metabolize organic macromolecules. The identified Cytophagales, Alteromonadales, Flavobacteriales, Fusobacteriales, Deferribacterales, Elusimicrobiales, Chlamydiales, Synergistales to mention but few, also catabolize macromolecules into smaller substrates to conserve energy. Furthermore, δ-Proteobacteria, Gloeobacteria and Clostridia affiliates syntrophically regulate PH2 and reduce metal to provide reducing equivalents. Methanomicrobiales and other Methanomicrobia species were the most prevalence Archaea, converting formate, CO2(g), acetate and methylated substrates into CH4(g). Thermococci, Thermoplasmata and Thermoprotei were among the sulfur and other metal reducing Archaea that contributed to redox balancing and other metabolism within treatments. Eukaryotes, mainly fungi were the least abundant guild, comprising largely Ascomycota and Basidiomycota species. Chytridiomycetes, Blastocladiomycetes and Mortierellomycetes were among the rare species, suggesting their metabolic and substrates limitations. Generally, we observed that environmental and treatment perturbations influenced communities' abundance, ß-diversity and reactor performance largely through stochastic effect. Understanding diversity of biogas microbiomes over wide environmental variables and its' productivity provided insights into better management strategies that ameliorate biochemical limitations to effective biogas production.