A Metabolic Study of Biohydrogen-Producing Photosynthetic Bacteria:The Effects on Growth Rates of Rhodobacter capsulatus JP91 Hup- and Rhodopseudomonas palustris when Acetate is replaced by Glucose as the Primary Carbon Source

The study of photosynthetic purple non-sulfur bacteria (PNSB) is a relatively new and encouraging field of biofuel research. These bacteria metabolize organic acids and, though less efficiently, sugars into hydrogen – a high-energy fuel source. If the efficiency of glucose-to-hydrogen conversion could be increased, many waste products could be directly converted into fuel. This project investigated relative growth performance of strains of PNSB when glucose replaced sodium acetate as the primary carbon source. The potential benefit of increased genetic diversity of mixed cultures was also explored. The growth rates of two bioreactors each containing Rhodobacter capsulatus JP91 Hup- were compared to those of two bioreactors populated with a consortium of PNSB (R. capsulatus JP91 Hup- and two strains of Rhodopseudomonas palustris). The bacterial cultures were grown anaerobically in constant flow photobioreactors. Growth rates were determined by measuring changes in biodensity. There was no significant difference in growth rates between monocultures and mixed cultures. However, the growth rates of bacteria on glucose were generally equal to or greater than those on acetate. This result suggests that further study of metabolic patterns of PNSB presented with various carbon sources may prove useful in exploring the viability of single-stage conversion of waste sugars into biohydrogen fuel. L’etude de bacteries pourpres non sulfureuses (BPNS) est relativement nouvelle et un domaine prometteur a l’egard de la recherche sur les biocarburants. Ces bacteries metabolisent les acides organiques et, bien que de facon moins efficaces, metabolisent aussi les sucres a l’hydrogene – une source de carburant a haute energie. Si l’efficacite de la conversion de glucose a hydrogene pouvait etre augmentee, de nombreux dechets organiques pourraient etre directement convertis en carburant. Ce projet a etudie le rendement de croissance relative des souches de BPNS lorsque le glucose fut remplace par de l'acetate de sodium comme source de carbone primaire. L'avantage potentiel de l'augmentation de la diversite genetique de cultures mixtes a egalement ete examine. Le taux de croissance des deux bioreacteurs contenant chacun Rhodobacter capsulatus JP91 Hup- ont ete comparees a deux bioreacteurs peuples avec un consortium de BPNS (R. capsulatus JP91 Hup-et deux souches de Rhodopseudomonas palustris). Les cultures bacteriennes ont ete cultivees anaerobiquement dans des photobioreacteurs a debit constant. Les taux de croissance ont ete determines en mesurant la variation de biodensite. Il n'y avait pas de difference significative dans le taux de croissance entre les monocultures et les cultures mixtes. Cependant, le taux de croissance avec le glucose etait generalement egale ou superieure compare a l’acetate. Ce resultat suggere que d'autres etudes du profils metaboliques de PNSB avec diverses sources de carbones peuvent s’averer utiles dans l'exploration de la viabilite de la conversion a etape simple de dechets organiques detenant du sucre en biohydrogene.