A biological multidisciplinary characterization of Rhodobacter capsulatus

Abstract

An extensive biological characterization of phototrophic bacterium R. capsulatus was performed to obtain relevant information for a possible medical use. Firstly, a weak anti-microbial activity against B. subtilis was found secreted from the cells. By all means examined, the bacteria was nontoxic: i. e., no biotoxicity was found positive when both cultured media and bacterial cells were tested in either ICR mice or JWR rabbits. Thirdly, to determine subcellular localization of the photosynthetic enzyme, ribulose 1,5-bisphosphate carboxylase/oxygenase, an immunoelectron microscopic examination was performed on ultra thin frozen sections of R. capsulatus. The immunoelectron microscopy revealed that even under aerobic conditions in darkness the enzyme that mediates the conversion of ribulose 1,5-bisphosphate to 3phosphoglycerate in the Calvin cycle was synthesized to localize at the chromatophores in the bacterial cells. Fourthly and lastly, to optimize the production of the biodegradable polymer, poly 3-hydroxybutyric acid (PHB), R. capsulatus was cultured under conditions that lacked nitrogen. The titration of mannitol as a carbon source showed that the production of PHB was maximized to occupy 78% of dried weight of bacteria when the cells were cultured in 1% mannitolcontaining medium. Unexpectedly, PHB was found synthesized even if the bacteria was cultured in the presence of nitrogen. The findings unraveled the previously poorly understood biolodical features of the bacteria and can pave the way for the possible medical use of R. capsulatus in near future.