Behaviour of Nif− mutants of Rhodobacter capsulatus in photosynthetic, ammonia-limited chemostat cultures

Abstract

Nif− mutants of Rhodobacter capsulatus carrying mutations either in the nifR4 regulatory gene or in the nifH structural gene both outgrew the wild-type strain B10 in mixed chemostat cultures under conditions favouring nitrogenase-mediated H2 production by the wild-type (ammonia as limiting nutrient, inert argon atmosphere, light as energy source), whereas under aerobic conditions in the dark, or in batch culture, the growth of Nif− mutants was not favoured. Nitrogenase-mediated H2 production therefore appears to be detrimental to the growth of R. capsulatus in nitrogen-limited continuous culture, as may also be the case for other nitrogen fixers.