Biohydrogen: Microbiology and Microbial Dynamics in Dark Fermentation

There is a global attention toward production of clean and green energy to reduce the dependency on fossil fuel-derived sources and its subsequent environmental impact. Biohydrogen, thus offers an attractive potential source of energy with both economic and environmental advantages. Hydrogen is produced biologically through light-driven and light-independent pathways. At present, light-independent process of dark fermentation appears more favorable due to low operational costs and high hydrogen yield, and thus, is advancing in research. Production involves a complex interplay of genetically and functionally diverse mixed microbial cultures with a multitude of organic substrates. The dominant types of microorganisms involved in these metabolic reactions function in mesophilic range and are both facultative and strict anaerobes, belonging to genera Clostridium and Enterobacter. However, with varying environmental and operational conditions, a shift occurs in the microbial community structure that further affects the yield of hydrogen produced. By understanding the syntrophic co-metabolism of hydrogen-producers and hydrogen-consumers, the bioreactor performance can be modified for scaling-up biohydrogen production in continuous systems. With modern molecular techniques and metagenomic studies, it is now becoming possible to study these reactor microbiomes to extract information about essential enzymes and respective microorganisms that may increase the hydrogen yield.