Some aspects of hydrogen, nitrogen and oxygen metabolism by heterocysts isolated from Anabaena sp. strain CA-V




Smith, Russell Lamar

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Metabolically active heterocysts were isolated from Anabaena sp. strain CA-V and showed high acetylene reduction and hydrogen evolution rates. Hydrogen production in the heterocysts exhibited biphasic kinetics consisting of a short intense one-two minute burst of hydrogen production upon illumination followed by a steady state rate of hydrogen evolution. The presence of 100 nM NiCl₂-6H₂O in the growth medium exerted an effect on both hydrogen production and acetylene reduction in heterocysts: hydrogen-stimulated acetylene reduction was increased from 41 to 75 μl C₂H₄ per mg dry wt per hour (1.8 to 3.3 μmol per mg dry wt per hour) and net hydrogen production under 1%CO₂-99% N₂ in the light was abolished. A light-dependent, nickel-stimulated hydrogen uptake was also observed in heterocysts isolated from cultures grown in the presence of 100 nM NiCl₂-6H₂O . When whole filaments were incubated with 100 nM ⁶³Ni, radioactivity was found in isolated heterocysts at levels about six times greater than in vegetative cells. In whole filaments as well as heterocysts under 1%CO₂-99%Ar, ethylene production rates approached a 1:1 ratio with hydrogen production. Hydrogen producing cells under an atmosphere of 1%CO₂-99%N₂ immediately increased their hydrogen production rates at least four-fold when sparged for two minutes with 1%CO₂-99%Ar. If the cells contained nickel, a much smaller, non-sustainable burst of hydrogen production was apparent before production ceased and uptake began. Isolated heterocysts were also shown to have an active oxygen uptake metabolism, 55 μl O₂ per mg dry wt per hour (2.5 μmol per mg dry wt per hour) in the light and 40 μl O₂ per mg dry wt per hour (1.8 μmol per mg dry wt per hour) in the dark, when purposely brought to air O₂ levels. These O₂ uptake rates are 4-5 times the respiratory rate of whole filaments and are, therefore, difficult to reconcile with the view that heterocysts are largely impermeable to O₂