Effect of palmitic acid utilization on cell division in Mycobacterium avium

Mycobacterium avium, a facultative pathogen for humans, undergoes a life cycle in which selected small cells elongate and then fragment to form coccobacilli. M. avium cells of uniform size were selected by membrane filtration and tested for growth and division in the presence or absence of palmitic acid. Growth was measured by increased cellular protein, and cell division was determined by increased colony-forming units on agar or, electronically, by increased numbers of particles. Both growth and division rates of M. avium were found to be dependent upon the initial concentration of palmitic acid presented to the cells. The division constant varied from 0.05 to 0.13 when the concentration of palmitic acid ranged from 0 to 175 nmol/ml of medium. With [(14)C]palmitic acid as a tracer, it was found that rapid cell division began upon cessation of fatty acid uptake. During division, new lipid materials were released which contained (14)C derived from [(14)C]palmitic acid. Limited cell division and no fragmentation occurred in fatty acid-starved cultures. During fatty acid starvation, the transparent colony form, considered a pathogen, underwent a transition to the colony form considered a nonpathogen. The possible relationships between the organism's dependence on fatty acid and its ability to infect humans are discussed.