Caracterizació ecofisiològica d'un mutant de Rhodobacter sphaeroides deficient en la síntesi de carotenoides

Abstract

A mutant strain of Rhodobacter sphaeroides, altered in carotenoid biosynthesis. was compared to the wild type in relation to the physiological response of both strains to different light intensities (230-925 lux). Absorption spectra analysis showed that spheroidene, the main carotenoid present in this species, was substituted by chloroxanthin (hydroxyneurosporene) in the mutant strain. The mutation does not affect significantly the growh of the mutant under neither photoorganoheterotrophic nor chemoorganoheterotrophic metabolisms. Mutant cells growing anaerobically at light intensities below 800 lux, surprisingly showed higher growth rates than wild type cells. At light intensities above 800 lux, growth rates of both strains were very similar. Growth rates in chemoorganotrophic metabolism were much higher than in photoorganotrophic growth for both strains. Although pigments do not intervene in nonphotosynthetic metabolism, the wild type strain showed a higher growth rate than the mutant strain. In addition to growth rate measurement, pigment content was studied in order to characterize the physiological behaviour of the mutant. In the wild type strain, specific pigment content decreased as light intensity increased. Bacteriochlorophyll and carotenoids showed the same response. On the contrary, for the mutant cells, bacteriochlorophyll specific content was much higher at high light intensities than at the lower ones. Carotenoids had very low specific content. which was independent of light intensity. Both the physiological implications and the possible ecological meaning of that behaviour are discussed.