Metagenomic survey of a biological tannery wastewater treatment plant in Modjo, Ethiopia Adey Feleke Desta*, Seyoum Leta***, Francesca Stomeo**, Joyce Nzioki ** Solomon Maina**,Moses Njahira** and Appolinaire Djikeng ** * Department of Cellular, Microbial and Molecular Biology, Addis Ababa University, Addis Ababa, Ethiopia ** Biosciences in Eastern and Central Africa (BecA), International Livestock Research Institute (ILRI), Nairobi, Kenya *** Center of Environmental Sciences, Addis Ababa University, Addis Ababa, Ethiopia * Department of Cellular, Microbial and Molecular Biology, Addis Ababa University, Addis Ababa, Ethiopia ** Biosciences in Eastern and Central Africa (BecA), International Livestock Research Institute (ILRI), Nairobi, Kenya *** Center of Environmental Sciences, Addis Ababa University, Addis Ababa, Ethiopia The leather industry generates high amount of liquid wastes constituting pollutants such as organic and inorganic matter, total dissolved solids as well as a variety of compounds, including the heavy metal chromium. Ethiopia has a long tradition of processing and exporting leather and leather products but pollution is the major problem that needs to be alleviated by establishing cost-effective wastewater treatment options. A well managed biological wastewater treatment process depends on the knowledge of the microbial populations residing in the sludge of the treatment system. Introduction This study was financially supported by the African Biosciences Challenge Fund (ABCF) Results & Discussion A cross- sectional study was conducted with the aim of analyzing the microbial community of an integrated biological system for the treatment of tannery wastewater in Modjo town, Ethiopia. The treatment system is composed of anaerobic and aerobic reactors integrated with constructed wetland (Fig. 2). cultivation- independent approach was used which involves extraction of metagenomic DNA from five representative sites of the treatment system and direct sequencing using the Illumina ® platform followed by sequence analyses. A total of 10,187,047 reads were obtained by sequencing the metagenomeic DNA from each site % of the reads were Bacteria, 0.1-3% Eukarya, 0.1 – 5% Archaea and 1% Viruses and uncultured microbes. Among the bacterial Phyla, diverse communities with the dominant members affiliated to Firmicutes (46.2%), Proteobacteria (20%) Actinobacteria (19%) and Bacteroidia (9%) were identified in the Anaerobic system (Fig. 3). In the aerobic system, Proteobacteria (83%) was the most abundant. The wetland sites have different abundant bacterial groups in each sampling site (Fig. 4) Conclusions Figure 2: Schematic presentation of the pilot tannery effluent treatment site The Shannon-Wiener (H) diversity index showed the highest diversity (H =5) for the samples from constructed wetland sites, followed by the anaerobic reactor with an index of 4.2. The site with the least diversity was the aerobic reactor (H= 3.9). The overall high bacterial diversity might be implicated in the removal of some of the major pollutants such as SO 4, S 2- and Chemical Oxygen Demand (COD); which were found to have removal efficiencies of 96, 91 and 97 percent respectively. Comparisons of richness based on calculations using rarefaction indicated that the number of clones sequenced from the anaerobic and aerobic reactors as well as the constructed wetland sites was not enough to cover the full bacterial diversity in the sites, which was expressed by the weakly curvilinear plots that failed to level- off (Fig. 4). Therefore, a more exhaustive bacterial sampling of the present sites would be necessary to obtain complete coverage. Figure 4: Composition of the observed bacterial Classes in the sites Figure 5: Cluster analysis based on Bray-Curtis distance measure for the identified microbial groups in the different sample sites This cross- sectional study showed the presence of diverse bacterial community in the different biological reactors working in concert for the efficient treatment of the complex tannery wastewater. Figure1:Leather products and the waste generated Figure 3: Composition of the observed bacterial phyla in the sites Analysis using non-metric Multi-Dimensional Scaling (nMDS) elucidated the rank and position of each sampling site with respect to the bacterial phylotype and frequency of the reads for each phylotype (Fig. 5). The anaerobic reactor harboured significantly different bacterial groups than the rest of the sites, while the aerobic site is not different from the constructed wetland sites in terms of the identified bacterial populations.