HYDROGEN UPTAKE IN NOSTOC STRAIN PCC-73102 - EFFECTS OF NICKEL, HYDROGEN, CARBON AND NITROGEN

The uptake hydrogenase activity was characterized in Nostoc sp. strain PCC 73102, a free-living filamentous heterocystous cyanobacterium ori ginally isolated from coralloid roots of the cycad Macrozamia sp., usi ng a H-2-electrode. We demonstrate the presence of a light-dependent h ydrogen uptake activity in nitrogen-fixing cells. The uptake was stimu lated by addition of Ni2+ to the growth medium up to a concentration o f 5 mu M Cultures, grown in continuous light in the presence of 9% H-2 , showed a clear enhancement of the hydrogen uptake. A temporary stimu lation of the light-dependent hydrogen uptake activity was also achiev ed by adding 9% of H-2 to cells incubated in darkness. Cells grown het erotrophically in complete darkness, reached four times higher light-d ependent hydrogen uptake than photoautotrophically grown cells. Additi on of the protein synthesis inhibitor chloramphenicol to heterotrophic ally grown cells, abolished the increase observed by the presence of o rganic carbon, indicating a regulation at the protein synthesis level and not by a regulation of pre-existing enzyme/subunit(s). No uptake a ctivity was observed in cells incubated in darkness only. In cultures grown with the presence of 5 mM ammonium chloride, significant reducti ons in both nitrogenase and light-dependent uptake hydrogenase activit y were observed. In summary, Hz, either added from an external source or produced through the action of nitrogenase, induced high in vivo li ght-dependent hydrogen uptake in the free-living cyanobacterium Nostoc PCC 73102.