Microcalorimetric Studies of the Toxic Action of La^(3+) on Halobacterium Halobium R1 Growth

A microcalorimetric technique was used to evaluate the influence of La 3+ on Halobacterium halobium R1 growth. By means of LKB 2277 bioactivity monitor, ampoule method at 37 ℃, the thermogenic curves of Halobacterium halobium R1 growth were obtained. In order to analyze the results, the maximum power P m and the growth rate constants k were determined, showing that values of P m and k are linked to the concentration of La 3+ . Addition of low concentration of La 3+ can cause a decrease of the maximum heat production and growth rate constant. However, high concentration of La 3+ may promote growth of Halobacterium halobium R1, but at much higher concentration of La 3+ , the growth of Halobacterium halobium R1 is inhibited again. For comparison, the shapes of Halobacterium halobium R1 cell were observed by means of transmission electron microscope. According to the thermogenic curves and TEM photos of Halobacterium halobium R1 under different conditions, it is clear that metabolic mechanism of Halobacterium halobium R1 growth is changed with the addition of La 3+ .