This study addresses for the first time the influence of initial pH on the evolution of microbial consortia in dark fermentation of scotta permeate, using a high-throughput sequencing approach. Three fermentation phases could be detected: 1) a lag phase with no substantial differences in microbial composition at different initial pH values; 2) an exponential H-2 production phase, accompanied by a general increase of Clostridium genus components and higher incidence of Trichococcus genus at neutral and alkaline pH; 3) a final stationary phase, characterized by a general increase of Bifidobacterium and Lactobacillus genera in all reactors. The initial pH value influenced the relative abundance of Trichococcus at 16-48 h of incubation. The metabolic activity of this genus increased the amount of metabolic precursors of H-2 so that, when pH lowered to 5.4, Clostridia in the reactors with initial alkaline pH become more active H-2-producers than those in the others. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.