FIG. 1.

Optical absorbance (A₅₈₀) and DNA content (genomes per milliliter) of cultures of M. tuberculosis H37Rv in the slowly stirred 0.5 HSR model. Aerobic growth occurs for approximately 60 h, after which the bacilli shift down to the microaerophilic NRP-1 stage until oxygen is completely depleted, when the culture is about 160 h old and bacilli shift down to the anaerobic NRP-2 stage. DNA synthesis stops abruptly as the bacilli enter NRP-1. This figure represents one of two independent experiments that gave comparable results. Symbols: A₅₈₀, solid circles; DNA, solid squares.