Sensitivity to lytic agents and DNA base composition of several aerobic spore-bearing bacilli

Abstract

The authors studied the possible relationship between a genetic characteristic, like DNA base composition, and certain phenotypic characteristics, i.e., sensitivity to lytic agents, morphology of colonies, and biochemical reactions in 34 strains of spore-bearing bacilli. From the results obtained two groups of bacilli have been identified. The first group includes the species B. subtilis, B. pumilus, B. licheniformis, and B. firmus and one strain of B. megaterium. The mean value of the GC% of the DNA is 44.22 +/- 1.76. All the strains examined are highly sensitive to lysozyme and resistant to sodium lauryl sulphate (S.L.S.); the surface colonies have a "rhizoid" appearance and the microcolonies on slide microculture are star-shaped. The second group includes the species B. cereus, B. cereus var. mycoides, B. anthracis, and B. thuringiensis. The mean value of the GC% of the DNA is 33.65 +/- 0.59. All the strains belonging to this group are resistant to both lysozyme and S.L.S., and the surface macro-colonies and the microcolonies have a "medusae head" appearance. The two groups also have certain different biochemical reactions; e.g., anaerobic growth and the egg yolk reaction, with few exception, are negative for the first group and positive for the second; furthermore, the strains in the first group (with rare exceptions) cause fermentation in the three carbohydrates, glucose, arabinose, and xylose, while glucose only is fermented by all strains with one exception in the second group. The position of B. megaterium is not yet clear, although one strain may certainly be included in the first group. Lysis by lipase is extremely variable and does not correlate with any of the other characteristics studied. The other species studied in relation to the characteristics, considered in our research (B. coagulans, B. macerans, B. polymyxa, B. laterosporus, B. alvei, B. circulans, B. stearothermophilus, and B. brevis), are not susceptible to grouping, either in the first, or in the second or even in a separate group.