The effect of temperature on the fatty acids and isozymes of a psychrotrophic and two mesophilic species ofXenorhabdus, a bacterial symbiont of entomopathogenic nematodes

In the first part of this study, generation times relative to temperature, together with cardinal and conceptual temperatures, were determined for four strains of Xenorhabdus bacteria that represented three geographically distinct species. The data showed that the NF strain of Xenorhabdus bovienii, like the Umeå strain of the same species, is psychrotrophic, while Xenorhabdus sp. TX strain resembles Xenorhabdus nematophila All strain in being mesophilic. In the second part, the capacity of these bacteria to adapt to changes in temperature, shown by changes in fatty acid composition, was investigated. As temperature declined, the proportions of the two major unsaturated fatty acids, palmitoleic (16:1ω7) acid and oleic (18:1ω9) acid, increased significantly in all of the strains. The proportion of the prevalent saturated fatty acid, which was palmitic acid (16:0), decreased. In the All, NF, and Umeå strains, myristic acid (14:0), margaric acid (17:0), cyclopropane (17:0c), and arachidic acid (20:0) decreased with decreasing temperature. In the third part of the study, the synthesis of isozymes in response to changing temperature was investigated. For the seven enzymes studied, the numbers for which isozyme synthesis was temperature related were as follows: five for Umeå, four for All, three for NF, and two for TX. Where the study dealt with fatty acid composition and isozyme synthesis, the results show a broad capacity for physiological temperature adaptation among strains of different climatic origin.Key words: Xenorhabdus, temperature, psychrotroph, mesophile, fatty acid, isozyme.