Impact of simple and complex substrates on the composition and diversity of microbial communities and the end-product synthesis
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The effect of simple and complex on the composition and diversity of microbial communities and on end-product (biogas and VFAs) synthesis was investigated using an anaerobic batch respirometer at 37 °C and pH 7.2. These experiments, simple substrates were chemically pure and contain a single carbon source (glucose or α-cellulose), while complex substrates were chemically “impure” substrates containing a mixture of two or three carbon sources (biodiesel-derived glycerol or wheat straw) with a substrate/inoculum ratio 6g chemical oxygen demand (COD)/ g volatile solids (VS) seed and 100g of pre-treated dairy manure digestate (DMD), respectively. Concentrations of hydrogen, carbon dioxide, acetate, butyrate, propionate, and ethanol synthesized by different communities selected by growth on the different substrates were measured and confirmed the growth of the microbial communities. 16S rDNA illumina sequencing revealed that DMD without substrates was more diverse than the microbiota cultured by fermentation reactions containing D-glucose, glycerol α-cellulose or wheat straw. The data confirmed that substrates play a crucial role in determining the diversity of species in microbial communities. Dominant operational taxonomic units (OTUs) belonging to families Clostridiaceae, Ruminococcaceae, and Enterobacteriaceae, and the genera Clostridium, Ruminococcus, Sporolactobacillus, and Syntrophomonas were potentially responsible for changes in end-product synthesis patterns in communities cultured with simple and complex substrates.