Anaerobes and methanogens dominate the microbial communities in water harvesting ponds used by Kenyan rural smallholder farmers

Benjamin H. Gregson^a, Alessia Bani^a, Laurel Steinfield^b, Diane Holt^c, Corinne Whitby^a

School of Life Sciences, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, UK.

Many rural smallholder farmers in Kenya use water-harvesting ponds, to collect rainwater, as sustainable sources of water for domestic and agricultural purposes. There is currently limited information regarding the microbial ecology in these ponds. Here, we used High Throughput Sequencing (HTS) to characterize the microorganisms present (including potential pathogens and indicator species) alongside ion chromatography to measure water chemistry (anion and cation concentration). Fluoride and magnesium concentration were the strongest predictor variables of the microbial community. Obligately or facultatively anaerobic bacterial genera (e.g. Spirochaeta and Opitutus) were abundant within the bacterial community, whilst Woesearchaeota and methanogens dominated the archaeal community. This suggests the water in the ponds is hypoxic or anoxic, and if used for irrigation, may potentially impact crop yield and viability. In addition, the opportunistic pathogen non-tuberculous mycobacteria (NTM), Mycobacterium fortuitum was found, comprising >1% of the bacterial community, suggesting a potential human health risk. Here we suggest low-cost changes to pond management, to improve or ameliorate pond anoxia and remove pathogens to benefit the livelihoods and welfare of these farms. This study also shows the applicability of HTS to broadly screen the microbial communities, assess water quality, and identify potentially pathogenic groups.

Keywords: Water harvesting, Microbial ecology, High Throughput Sequencing, Pathogens, Microbial quality, Chemical quality, Amplicon.