Effect of heat stress on cell activity and cell morphology of the tropicalrhizobium, Sinorhizobium arboris

The effect of heat stress oil the growth, physiological state, cell activit y and cell morphology of the tropical Sinorhizobium ariboris strain HAMBI 2 190 was studied. The cells were chromosomally tagged with the firefly lucif erase gene, luc. Since the bioluminescence phenotype is dependent on cellul ar energy reserves it was used as an indicator of the metabolic status of t he cell population under various heat conditions. Variations in the numbers and lengths of growth phases between individual cultures indicated that th e growth pattern at 40 degreesC was disturbed compared to growth at 37 or 2 8 degreesC. In addition, the cell morphology was changed radically. The num ber of culturable cells and the luciferase activity declined when the cultu res were incubated at 40 degreesC. By contrast, under all conditions studie d, the cells could be stained with 5-(and 6-)sulfofluorescein diacetate, in dicating esterase activity. This demonstrated that although the culturabili ty and cellular energy reserves decreased considerably during heat stress, a majority of the of S. arboris cell population maintained basal enzyme act ivity. (C) 2001 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.