Effect of Temperature on the Growth Rates of Rhizobia

Abstract

The literature is surprisingly deficient in data showing quantitatively the effect of temperature on growth rates of rhizobia. In most studies the effect of temperature has been reported in terms of total growth observed, often on agar plates, and after three or more days. Obviously such data furnish little information on comparative growth rates at different temperatures, since total growths after a considerable growth period tend to be nearly the same regardless of the initial rates. The data reported in the present paper for several strains of rhizobia were obtained for the primary purpose of establishing rather accurately the optimum temperature for growth. Beijerinck (1888) stated that room temperature was the most favorable for clover bacteria. Laurent (1891) obtained the best growths at 220 to 260C.; at 300C. the growth was no better than at the lower range. DeRossi (1910) found the optimum to vary between 250 and 300C. No growth was obtained at 370C. and frequently not at 350C. Zipfel (1911) obtained the best growths at 180 to 200C. Burrill and Hansen (1917) state that the optimum is 25° to 280C. In 24-hour experiments reported by Muller and Stapp (1925) with bacteria from several species of legumes, Rhizobium meliloti was the most heat resistant species. The optimum temperature for this organism was 280 to 300C., whereas other species preferred lower temperatures. Usually 320 to 330C. was harmful for most rhizobia. Fred, Baldwin and McCoy (1932) state that the optimum is between 200 and 280C.