Induction of a futile Embden-Meyerhof-Parnas pathway in Deinococcus radiodurans by Mn: possible role of the pentose phosphate pathway in cell survival.
Statistical models were used to predict the effects of tryptone, glucose, yeast extract (TGY) and Mn on biomass formation of the highly radioresistant bacterium Deinococcus radiodurans. Results suggested that glucose had marginal effect on biomass buildup, but Mn was a significant factor for biomass formation. Mn also facilitated glucose interactions with other nutrient components. These predictions were verified by in vivo and in vitro experiments. TGY-grown cells metabolized glucose solely by the pentose phosphate pathway (PPP). Although only a fraction of glucose from the medium was transported into the cells, glucose was incorporated into the DNA efficiently after cells were exposed to UV light. The presence of glucose also enhanced the radioresistance of the culture. Mn could induce an Embden-Meyerhof-Parnas (EMP) pathway in D. radiodurans. The EMP pathway and the PPP of the Mn-treated cells oxidized glucose simultaneously at a 6:1 ratio. Although glucose was hydrolyzed rapidly by the Mn-treated cells, most glucose was released as CO(2). Mn-treated cultures retained less glucose per cell than cells grown without Mn, and still less glucose was incorporated into the DNA after cells were exposed to UV light. Mn-treated cells were also more sensitive to UV light. Results suggested that metabolites of glucose generated from the PPP enhanced the survival of D. radiodurans. Induction of the EMP pathway by Mn may deplete metabolites for DNA repair and may induce oxidative stress for the cell, leading to reduction of radioresistance.