Hydrogen production by immobilized cells—I. light dependent dissimilation of organic substances by Rhodopseudomonas palustris

Abstract

Photoproduction of H 2 from some organic acids by agar entrapped cells of Rhodopseudomonas palustris has been investigated. With an agar layer 3.5 mm thick, the rate of H 2 evolution from dl-malate is limited by the diffusion of the substrate into the agar when the concentration of bacterial cells is as high as 1.7 mg cells dry weight cm −3 ( ca. 0.59 mg cells d.w.cm −2) while no limitation occurs with 0.425 mg cells d.w.cm −3 ( ca. 0.15 mg d.w.cm −2). At the latter concentration of bacterial cells in the agar layer, the rate of H 2 evolution is light saturated at an energy flux of 2.7 × 10 3 erg cm −2 s −1. Immobilized cells retain their H 2-producing activity much longer than the free cells kept in identical conditions. The conversion efficiency (H 2-formed divided by the the H 2-content of the substrate decomposed × 100) varied between 67% (succinate) and 40% (acetate).