Microbial consortia for hydrogen production enhancement.

Ten efficient hydrogen-producing strains affiliated to the Clostridium genus were used to develop consortia for hydrogen production. In order to determine their saccharolytic and proteolytic activities, glucose and meat extract were tested as fermentation substrates, and the best hydrogen-producing strains were selected. The C. roseum H5 (glucose-consuming) and C. butyricum R4 (protein-degrading) co-culture was the best hydrogen-producing co-culture. The end-fermentation products for the axenic cultures and co-cultures were analyzed. In all cases, organic acids, mainly butyrate and acetate, were produced lowering the pH and thus inhibiting further hydrogen production. In order to replace the need for reducing agents for the anaerobic growth of clostridia, a microbial consortium including Clostridium spp. and an oxygen-consuming microorganism able to form dense granules (Streptomyces sp.) was created. Increased yields of hydrogen were achieved. The effect of adding a butyrate-degrading bacteria and an acetate-consuming archaea to the consortia was also studied.

Methanogenesis in the sediments of Rio Tinto, an extreme acidic river.

Río Tinto (Iberian Pyritic Belt, SW Spain) is well known for its low pH (mean pH 2.3), high redox potential (> +400 mV) and high concentration of heavy metals. In this work we describe and analyse the presence of methanogenic archaea in the extreme acidic and oxidizing environment of the Tinto basin. Methane formation was measured in microcosms inoculated with sediments from the Rio Tinto basin. Methanol, formate, volatile fatty acids and lactate stimulated the production of methane. Methane formation was associated with a decrease of redox potential and an increase in pH. Cores showed characteristic well-defined black bands in which a high acetate concentration was measured among the otherwise reddish-brown sediments with low acetate concentration. Methanosaeta concilii was detected in the black bands. In enrichment cultures, M. concilii (enriched with a complex substrate mixture), Methanobacterium bryantii (enriched with H(2)) and Methanosarcina barkeri (enriched with methanol) were identified. Our results suggest that methanogens thrive in micro-niches with mildly acidic and reducing conditions within Rio Tinto sediments, which are, in contrast, immersed in an otherwise extremely acidic and oxidizing environment.

Phenotypic properties and microbial diversity of methanogenic granules from a full-scale upflow anaerobic sludge bed reactor treating brewery wastewater.

Methanogenic granules from an anaerobic bioreactor that treated wastewater of a beer brewery consisted of different morphological types of granules. In this study, the microbial compositions of the different granules were analyzed by molecular microbiological techniques: cloning, denaturing gradient gel electrophoresis and fluorescent in situ hybridization (FISH), and scanning and transmission electron microscopy. We propose here that the different types of granules reflect the different stages in the life cycle of granules. Young granules were small, black, and compact and harbored active cells. Gray granules were the most abundant granules. These granules have a multilayer structure with channels and void areas. The core was composed of dead or starving cells with low activity. The brown granules, which were the largest granules, showed a loose and amorphous structure with big channels that resulted in fractured zones and corresponded to the older granules. Firmicutes (as determined by FISH) and Nitrospira and Deferribacteres (as determined by cloning and sequencing) were the predominant Bacteria. Remarkably, Firmicutes could not be detected in the brown granules. The methanogenic Archaea identified were Methanosaeta concilii (70 to 90% by FISH and cloning), Methanosarcina mazei, and Methanospirillum spp. The phenotypic appearance of the granules reflected the physiological condition of the granules. This may be valuable to easily select appropriate seed sludges to start up other reactors.