Morphological and ultrastructural variations inAzotobacter vinelandii growing in oxygen-controlled continous culture

Abstract

Membrane development as a response to growth at different oxygen tensions (from about 1% to 100% saturation of the medium with air) was determined inAzotobacter vinelandii strain OP. The organisms were grown in a carbonlimited chemostat either on atmospheric nitrogen or on ammonium as nitrogen sources. Both types of cultures increased not only the number of intracytoplasmic membrane vesicles per cell but also the cell volume with aeration. As the ratio of length per width stayed largely constant increases of volume resulted in decreases of the cell surface area, representing the surface area of the peripheral cytoplasmic membrane, per cell volume. While in nitrogen-fixing cells the proportion of intracytoplasmic membrane surface area per cytoplasmic membrane surface area increased from 1:2 to 3:1 the ratio stayed almost constant in ammonium-assimilating cells. The data suggest that oxygen controls changes in the ratio of intracytoplasmic to cytoplasmic membrane surface areas only under conditions of nitrogen fixation.