Cell density-dependent growth of Myxococcus xanthus on casein

Abstract

When Myxococcus xanthus FB was grown on 0.2% casein it exhibited a phenomenon we call cooperative growth. That is, above 104 cells per ml, both strains that were studied exhibited increasing growth rates as a function of increasing cell numbers. Between 104 and 107 cells per 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 two 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 measurable growth on casein in liquid media, and we have calculated that the average concentration of hydrolyzed casein in the medium was indeed too low to support growth. At low cell densities, growth on hydrolyzed casein (Casitone) was normal and independent of cell concentration. Demonstration of cooperative growth at higher cell densities supports the suggestion that the communal behavior of myxobacteria results in more efficient feeding.

Changes in group size during resource shifts reveal drivers of sociality across the tree of life

“…Larger groups, therefore, may be able to better defend resources from others, as with coyotes 5 , or ants that utilize cooperative transport, carrying large resources to the nest, thus removing them from competition 86, 87 . Alternatively, collective feeding of a resource comprised of many components can permit the consumption of a larger fraction of that resource, such as biofilms that encapsulate a resource and slow the diffusion of nutrients 88, 89 , or humpback whales that use bubble nets to feed on a school of fish 90 .…”

Extracellular biology ofMyxococcus xanthus

“…Likewise, the function and importance of the many potentially secreted proteins in predation are currently unknown. The degradation of polymers is thought to be a cooperative process (Rosenberg et al, 1977). Thus, if casein is the sole carbon source, then M. xanthus cells only show significant growth above a certain cell density and the growth rate increases with increasing cell density.…”

Deciphering the hunting strategy of a bacterial wolfpack

“…To determine if high cell density is necessary for predation, Rosenberg et al (1977) showed that growth in liquid culture on the macromolecule casein is dependent on a high cell density of M. xanthus. Yet, when cultured with hydrolyzed casein, no significant difference in growth rate was observed in cultures with either high or low M. xanthus cell density.…”

“…Thus, it will be important for future research to establish whether M. xanthus shows cell density-dependent gene expression of degradative enzymes. Alternatively, regulation could occur at the level of the secretory apparatus or, as Rosenberg et al (1977) proposed, exoenzyme production may be constitutive, and the difference in growth rate could be attributed to reaching a critical extracellular threshold of hydrolytic enzymes required. Also important will be to establish how protein secretion in a shaking flask culture relates to secretion on solid surfaces where diffusion is more limited, and how hydrolysis of the casein protein compares with the lysis of prey.…”