PubMedDate not supplied
We conducted a comparative study of the effects of alpha-amino-gamma-butyrolactone, the common structural element of extracellular microbial regulators of the homoserine lactone (HSL) group, and of 4-n-hexylresorcinol, an autoregulator of the alkylhydroxybenzene (AHB) group, on the growth and development of gram-positive and gram-negative bacteria. We revealed non-species-specific effects of HSL and AHB and characterized their concentration dependencies. The addition of 10(-5)-10(-3) M HSL or 10(-5)-10(-4) M AHB during the exponential growth phase of the cultures grown on balanced media resulted in cell division arrest and accelerated the transition to the stationary phase that culminated in endospore formation in Bacillus cereus, Alicyclobacillus tolerans, and Sulfobacillus thermosulfidooxidans. When bacilli grew under the cultivation conditions that resulted in a low-zero spore percentage, 10(-4)-10(-3) M HSL cancelled the inhibition of spore formation. In the gram-negative bacteria Pseudomonas aurantiaca and Azotobacter vinelandii, AHB at concentrations of 10(-4) to (1.5-2.5) 10(-4) M induced the formation of dormant cells. Studies with the actinobacterium Streptomyces avermitilis revealed that the HSL effect varied depending on the age of the test cultures. The addition of 10(-4) M HSL during the lag phase of a submerged streptomycete culture accelerated its transition to the stationary phase and induced the formation of endospores, the dormant cells that are regarded as alternatives to exospores (conidia). If HSL (3.64 and 4.55 mg per 1cm2 disc) was locally added to a surface S. avermitilis culture, the growing mycelium formed rings that differed in their density, in the extent of the development of aerial mycelium, and in the presence/absence of exospores. Ring-shaped growth of streptomycete mycelia was also induced by 0.075-0.75 mg of AHB; however, unlike HSL, AHB repressed exospore formation. The data on non-species-specific effects of HSL and AHB suggest that they may perform regulatory functions on the microbial community level.