Studies on the Thermal Sensitivity of Marine Bacteria

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Abstract
Significantly fewer bacteria from sea water and recent marine sediments form colonies on nutrient agar when plated at 45[degree]C or higher than on that plated at 42[degree], the latter being the temp. at which nutrient agar begins to congeal. Using nutrient gelatin which congeals at a lower temp. it was found that only 81 to 83% as many colonies developed when the medium was plated at 45[degree] as on that plated at 30[degree]. Bacteria from lake water are similarly heat-sensitive. About 25% of the bacteria occurring in sea water or marine sediments are killed by being held at 30[degree] for 10 min., and 80% of them are killed at 40[degree] in 10 min. Studies on the O2 uptake of suspensions of marine bacteria after being subjected to different temps. show that the respiratory enzymes of some are inactivated in 10 min. at 30[degree]C. Most of the bacteria isolated from the sea multiply at near zero temp. but their apparent optimum is considerably higher than the environment which they inhabit. The most colonies were found on plates which were incubated at 18[degree] to 22[degree]C for a week or two. The observations demonstrate certain anomalies in the relationship of marine bacteria to temperature, and they emphasize the extreme thermal sensitivity of indigenous spp.