The main aim of this study was to investigate biological hydrogen production from sucrose and molasses by purple non-sulphur bacteria (PNS). The hydrogen production capacities of four different PNS bacteria (Rhodobacter capsulatus (DSM 1710), Rhodobacter capsulatus YO3 (Hup-), Rhodopseudomonas palustris (DSM 127) and Rhodobacter sphaeroides O.U.001 (DSM 5864)) were tested on sucrose and molasses. The photobiological hydrogen production were performed in 50 ml and 150 ml small scale photobioreactors, in batch mode. The produced hydrogen quantities, bacterial growth profiles and pH of the media were recorded through the photobiological hydrogen production processes. Organic acids and sucrose consumption rates were determined by HPLC during the experiments. The maximum hydrogen productivitiy of 0.78 (mmol/lc.h) and 0.55 (mmol/lc.h) was obtained by R. palustris (DSM 127) on sucrose and molasses, respectively. Secondly, co-cultivation of these bacterial strains was studied. The maximum hydrogen productivity by co-cultivation of R. sphaeroides O.U.001 (DSM 5864) and R. palustris (DSM 127) was found as 1.0 (mmol/lc.h).

Mercury (Hg) is a global pollutant and potent neurotoxin that bioaccumulates in aquatic and terrestrial food webs as monomethylmercury (MeHg). Anaerobic microbes are largely responsible for MeHg production, which depends on the bioavailability of inorganic Hg substrates to methylators. Hg redox cycling pathways such as Hg reduction play a key role in determining Hg’s availability in the environment. Although abiotic photochemical Hg reduction typically dominates in oxic surface environments, Hg reduction pathways mediated by photosynthetic and anaerobic microbes are thought to play an important role in anoxic habitats where light is limited and MeHg production occurs. Currently, the physiological mechanisms driving phototrophic and anaerobic Hg reduction remain poorly understood. The main objective of my thesis is to provide mechanistic details on novel anaerobic and phototrophic Hg reduction pathways. I used a combination of physiological, biochemical and trace Hg analytical techniques to study Hg reduction pathways in a variety of anaerobic and photosynthetic bacteria. I demonstrated that Hg redox cycling was directly coupled to anoxygenic photosynthesis in aquatic purple non-sulphur bacteria that reduced HgII when cells incurred a redox imbalance. I discovered that terrestrial fermentative bacteria reduced Hg through pathways that relied on the generation of reduced redox cofactors. I also showed that sulphur assimilation controlled Hg reduction in an anoxygenic phototroph isolated from a rice paddy. In addition, I developed methods to explore cryptic anaerobic Hg redox cycling pathways using Hg stable isotope fractionation. At its core, my thesis underscores the intimate relationship between cell redox state and microbial Hg reduction and suggests a wide diversity of microbes can participate in anaerobic Hg redox cycling.