Title

Studies On The Hydrogen Metabolism Of Marine Cyanobacteria

Date of Award

1984

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Marine Biology and Fisheries

Abstract

H(,2) photoproduction, acetylene photoreduction and O(,2) dependent H(,2) uptake activity were compared in 63 marine cyanobacteria from this laboratory's collection. Non-hetercystous filamentous and aerobic nitrogen fixing unicellular forms were able to accumulate H(,2) for longer periods of time in closed vessels, whereas heterocystous filamentous forms were not able to accumulate hydrogen. The uptake hydrogenase activity was found to be one of the major factors decreasing net H(,2) production and accumulation.H(,2) photoproduction by one of the aerobic nitrogen fixing unicellular cyanobacteria, Synechococcus sp.Miami BG 043511 was studied in detail. Early log phase cells of this cyanobacterium cultured under nitrogen fixing conditions evolved H(,2) at a maximum rate of 2,000 nmoles/mg dry wt/hr or 250 umoles/mg chl./hr. and produced H(,2) and O(,2) simultaneously in the molar ratio of 2:1 for 120 hours. During this period, there was no net change in cellular carbohydrate level. These and other data indicated that water was the ultimate source of H(,2). The stoichiometric ratio of H(,2) and O(,2) produced from water was maintained under light saturated conditions. Light limitation caused evolution of CO(,2) along with H(,2) and O(,2) and resulted in a H(,2) to O(,2) molar ratio greater than two. The molar ratio of H(,2) to O(,2) was decreased by the addition of CO(,2).The ratio of H(,2) production to acetylene reduction was found to be close to one. O(,2) dependent H(,2) uptake activity was detected in log phase cells to a lesser extent. Very low levels of this activity (less than 1% of hydrogen production) was found in stationary phase cells. These data indicated that nitrogenase was the predominant enzyme responsible for H(,2) production. The experiments of nitrogen and ammonia pretreatment showed that both H(,2) and O(,2) photoproduction were inhibited to the same degree; however, the molar ratio of H(,2) to O(,2) remained 2.0. In the presence of DCMU an immediate switching of electron donation from water to internal carbohydrates was found. These data suggest that stoichiometric hydrogen and oxygen photoproduction in aerobic nitrogen fixing unicellular Synechococcus sp. Miami BG 043511 is possible only when water is the electron donor.

Keywords

Chemistry, Biochemistry

Link to Full Text

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