Factors Contributing to the Bacteriolytic Effect of Species of Myxococci upon Viable Eubacteria

Abstract

ALTHOUGH the lytic effect of certain myxobacteria upon the true bacteria (eubacteria) has been known for some years1–4, the mechanism of the process is imperfectly understood, and no one seems hitherto to have studied the possible production of antibiotic substances by the first-named group of microorganisms. One of us (B.N.S.) has recently shown5 that some species of the Myxococcaceae undoubtedly cause lysis of living as well as dead bacteria, particularly upon solid non-nutrient media, but attempts to grow the lytic strains in suspensions of eubacteria in very dilute salt solution succeeded only when the latter were mostly non-viable. A possible explanation of this apparent anomaly is that the growth of the myxococcus concerned, upon dead bacteria or their products of disintegration, results in the production of a true non-enzymic antibiotic substance capable of killing viable eubacteria and so rendering them susceptible to lysis by the exocellular enzymes previously elaborated by the growing myxococci. If, therefore, an inoculum of myxococcal microcysts is made into a suspension of chiefly viable bacteria in a liquid, the minute amount of growth which can take place quickly upon the few dead bacteria will be insufficient to produce a high enough uniform concentration of antibiotic substance to kill any viable bacteria, and so growth ceases; but if an inoculation is made upon a dense mass of eubacteria on a solid medium, diffusion of metabolites is hindered and a high enough concentration of antibacterial substance is built up in the vicinity of the inoculum to kill some of the viable cells in that region and so enable growth of the myxobacterium to continue with progressive lysis of the eubacterial mass. We present below some evidence concerning the separation of the soluble non-enzymic antibiotic substance from the accompanying exocellular lytic enzymes which are active against non-viable bacteria only.