Detailed experiments were designed to evaluate the function of load-shock treatment strategy (50 g COD/l; 3 days) for selective enrichment of acidogenic hydrogen (H-2) producing consortia in comparison with untreated anaerobic consortia. Experiments performed in suspended-batch mode bioreactors for 520 days illustrated the relative efficiency of load-hock treated consortia in enhancing H-2 production (16.64 mol/kg CODR) compared to untreated-parent consortia (3.31 mol/kg CODR). On the contrary, substrate degradation was higher with control operation (xi(COD), 62.86%; substrate degradation rate (SDR), 1.10 kg CODR/m(3)-day) compared to load-shock culture (52.33%; 0.78 kg CODR/m(3)-day). Fatty acid composition documented a shift in the metabolic pathway towards acetate formation after applying load-shock, which manifests higher H-2 production. Microbial profiling documented a significant alteration in species composition of microbial communities after repeated load-hock applications specific to enrichment of Firmicutes which are favourable for H-2 production. Dehydrogenase activity was stabilized with each re-treatment, signifying the adaptation inclination of the biocatalyst towards increased proton shuttling between metabolic intermediates, leading to higher H-2 production. Voltammograms of load-shock treated cultures showed a marked shift in oxidation and reduction catalytic currents towards more positive and negative values respectively with increasing scan rate evidencing simultaneous redox-conversion reactions, facilitating proton gradient in the cell towards increased H-2 production. Load-shock treatment facilitates direct cultivation of inoculums at higher substrate load without any chemical pretreatment. This study documented the feasibility of controlling microbial metabolic function by application of load-shock treatment either for preparing inoculum for startup of the reactor or to the reactor resident microflora (in situ) during operation whenever required to regain the process performance. Copyright (c) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.