bacteriochlorophylls and malic-acid

Rhodobacter sphaeroides is a purple non-sulfur bacterium which photoheterotrophically produces hydrogen from organic acids under anaerobic conditions. A gene coding for putative chlorophyll a synthase (chlG) from cyanobacterium Prochlorococcus marinus was amplified by nested polymerase chain reaction and cloned into an inducible-expression plasmid which was subsequently transferred to R. sphaeroides for heterologous expression. Induced expression of chlG in R. sphaeroides led to changes in light absorption spectrum within 400-700 nm. The hydrogen production capacity of the mutant strain was evaluated on hydrogen production medium with 15 mM malate and 2 mM glutamate. Hydrogen yield and productivity were increased by 13.6 and 22.6%, respectively, compared to the wild type strain. The results demonstrated the feasibility of genetic engineering to combine chlorophyll and bacteriochlorophyll biosynthetic pathways which utilize common intermediates. Heterologous expression of key enzymes from biosynthetic pathways of various pigments is proposed here as a general strategy to improve absorption spectra and yield of photosynthesis and hydrogen gas production in bacteria.

Topics: Bacteriochlorophylls; Carbon-Oxygen Ligases; Chlorophyll; Chlorophyll A; Cloning, Molecular; Gene Expression; Genes, Bacterial; Genetic Engineering; Glutamic Acid; Hydrogen; Malates; Mutation; Photosynthesis; Plasmids; Polymerase Chain Reaction; Prochlorococcus; Recombinant Proteins; Rhodobacter sphaeroides

Two local hydrogen-evolving strains of purple nonsulfur bacteria have been isolated, characterized, and identified as Rhodopseudomonas sp. TUT (strains Rh1 and Rh2). Lactate followed by succinate and malate supported the highest amounts of H2 production, growth (O.D.660nm, proteins and bacteriochlorphyll contents), nitrogenase activity, and uptake hydrogenase; the least of which was acetate. Alginate-immobilized cells evolved higher hydrogen amounts than free cell counterparts. Rh1 was more productive than Rh2 at all circumstances. Lactate-dependent hydrogen evolution was more than twice that of acetate, due to ATP productivity (2/-1, respectively), which is limiting to the nitrogenase activity. The preference of lactate over other acids indicates the feasibility of using these two strains in hydrogen production from dairy wastewater.

Topics: Acetic Acid; Adenosine Triphosphate; Alginates; Bacteriochlorophylls; Cells, Immobilized; Energy Metabolism; Glucuronic Acid; Hexuronic Acids; Hydrogen; Hydrogenase; Kinetics; Lactic Acid; Malates; Nitrogenase; Photosynthesis; Rhodopseudomonas; Succinic Acid