Cell density-dependent growth of Myxococcus xanthus on casein

Abstract

When M. xanthus FB was grown on 0.2% casein it exhibited a phenomenon called cooperative growth. Above 104 cells/ml both studied strains exhibited increasing growth rates as a function of increasing cell numbers. Between 104-107 cells/ml the mean doubling times of strains YS and TNS decreased from 15.2 to 8 h and 26 to 8.5 h, respectively. The extracellular proteinase activity of the 2 strains was equivalent and directly proportional to cell number. Cooperative growth was correlated with increased concentration of hydrolyzed casein in the medium, suggesting cooperative hydrolysis of casein. At low cell densities neither strain was capable of measureable growth on casein in liquid media, and the average concentration of hydrolyzed casein in the medium was too low to support growth. At low cell densities growth on hydrolyzed casein (Casitone) was normal and independent on cell concentration. Demonstration of cooperative growth at higher cell densities indicates that the communal behavior of myxobacteria results in more efficient feeding.