Carbon allocation in wild-type and Glc+ Rhodobacter sphaeroides under photoheterotrophic conditions

The photosynthetic bacterium Rhodobacter sphaeroides is capable of producing H2 via nitrogenase when grown photoheterotrophically in the absence of N2. By using 14C-labeled malate, it was found that greater than 95% of this substrate was catabolized completely to CO2 during H2 production. About 60% of this catabolism was associated with H2 biosynthesis, while almost 40% provided reductant for other cellular purposes. Thus, only a small fraction of malate provided carbon skeletons. The addition of ammonium, which inhibited nitrogenase activity, increased substrate conversion into carbon skeletons threefold. Catabolism of malate occurred primarily via the tricarboxylic acid cycle, but gluconeogenesis was also observed. The wild-type organism grew poorly on glucose, accumulated gluconate and 2-keto-3-deoxygluconate, and did not produce H2. More than 50% of metabolized glucose appeared in carbon skeletons or in storage compounds. A glucose-utilizing mutant was five times more effective in utilizing this substrate. This mutant produced H2 from glucose, using 74% of metabolized substrate for this purpose. Glucose converted to storage products or to other carbon skeletons was reduced to 8%. Fixation of CO2 competed directly with H2 production for reducing equivalents and ATP. Refixation of CO2 released from these substrates under H2-producing conditions was, at most, 10 to 12%. Addition of ammonium increased refixation of respired CO2 to 83%. Patterns of carbon flow of fixation products were associated with the particular strains and culture conditions.</jats:p

Hydrogen formation in nearly stoichiometric amounts from glucose by a Rhodopseudomonas sphaeroides mutant

Rhodopseudomonas sphaeroides produces molecular H2 and CO2 from reduced organic compounds which serve as electron sources and from light which provides energy in the form of adenosine 5'-triphosphate. This process is mediated by a nitrogenase enzyme. A mutant has been found that, unlike the wild type, will quantitatively convert glucose to H2 and CO2. Techniques for isolating other strains capable of utilizing other unusual electron sources are presented. Metabolism of glucose by the wild-type strain leads to an accumulation of gluconate. The isolated mutant strain does not appear to accumulate gluconate.</jats:p

Relation between chemical composition of Grateloupia doryphora (Montagne) Howe, Gymnogongrus griffithsiae (Turner) Martius, and abiotic parameters

In Grateloupia doryphora and Gymnogongrus griffithsiae the seasonal variation of their chemical compounds was studied, establishing a relation with the physical and chemical properties of seawater. High values of proteins in the studied species were detected during the winter, 28.88% in G. doryphora and 26.68% in G. griffithsiae, corresponding to the maximum period of ammonium concentration in the marine environment. The variation in carbohydrates content showed an inverse relation with the proteins, with a maximum of 54.72% in G. doryphora and of 55.36% in G. griffithsiae, both in summer, positively correlated with salinity and temperature of sea water. Lipids content was low in both species. In G. doryphora the values ranged between 0.81 and 1.30% and, in G. griffithsiae, from 0.71 to 1.50% of dry weight, showing a direct relation with the amount of nitrogen in the seawater. The maximum content of ashes, phosphorus and potassium occurred in autumn and winter, respectively, with 11.85%, 0.20%, 1.27% in G. doryphora, and 14.46%, 0.14%, 1.41% in G. griffithsiae