Inhibitory effect of Jatropha curcas seeds on microbial communities in anaerobic digestion using 16S rRNA gene analyses

In the present study, the inhibitory effects of Jatropha curcas seeds were evaluated on fermentative and methanogenic microbial communities using 16S rRNA genes at optimized organic loading rates and different hydraulic retention time during anaerobic digestion process in continous reactors. Four different types of substrates were designed from J. curcas seeds; whole seed (JWS), Jatropha oil (JO), Jatropha pressed cake (JPC) and methanolic residues (MR). The JWS and JO have higher concentration of long chain fatty acids and other inhibitory compounds compared to methanolic residues and and pressed cake. The microbial DNA was extracted from effluents obtained from these four substrates treating reactors and were analysed using Illumina sequencing of 16S rRNA gene. The relative abundance of fermentative bacterial communities was reduced in long chain fatty acids rich samples (JWS and JO) compared to JPC and MR. On the contrary, the methanogenic communities were more dominated in JO and JWS compared to JPC and MR treating reactors. The outcomes of this study contribute to a better understanding that long chain fatty acids containing compounds (JO and JWS) inhibit the fermentative bacteria compared to methanogenic communities.