Psychrotrophic bacteria isolated from a constantly warm tropical environment

Psychrotrophic bacteria are known to occur in temperate, constantly cold, and artificially cooled environments. This is the first report of their occurrence in a constantly warm (ca. 24 degrees-35 degrees C) tropical environment. Soil samples taken from two sites along the southeastern coastal zone of Jamaica yielded growth of psychotrophic bacteria after 3-4 weeks of enrichment culture in 1/30 strength tryptic soy broth, 20 mg L-1 cycloheximide at 2 degrees C. Growth of individual isolates at 2 degrees C was confirmed. Isolates include aerobic and fermentative Gram-negative rods and sporeforming (Bacillus sp.) and non-sporeforming (Aureobacterium sp.) Gram-positive rods. We determined the effect of temperature on growth rate in four isolates. Strain Y1 has an unusually wide temperature range for growth, 2 degrees-44 degrees C, resembling that of Listeria monocytogenes. In strain R1 the optimum temperature for growth occurred unusually near the maximum temperature for growth. Strains R2 and Y2 displayed cardinal temperatures typical of known psychotrophs but appear to have evolved enhanced growth potential near the optimum temperature in response to a constantly warm environment.