Intracellular Accumulation of the Monomeric Precursors of Polyphosphates and Polyhydroxyalkanoates in Acinetobacter calcoaceticusand Escherichia coliCells

The formation of polyhydroxyalkanoates granules in anaerobically grown Escherichia coliM-17 cells was found to be preceded by the intracellular accumulation of carbonic acids (predominantly, acetic acid), amounting to 9% of the cytosol. The intracellular concentration of acidic metabolites increased after the lyophilization of the bacterial biomass and decreased after its long-term storage (3.5–13.5 years). The decrease in the concentration of acidic metabolites is likely due to the dehydration of dimeric carbonic acids in the viscoelastic cytosol of resting bacterial cells. The hydrophobic obligately aerobic cells of Acinetobacter calcoaceticusIEGM 549 are able to utilize a wide range of growth substrates (from acetate and citrate to hydrophobic hydrocarbons), which is considerably wider than the range of the growth substrates of E. coli(predominantly, carbohydrates). The minimal essential and optimal concentrations of orthophosphates in the growth medium of A. calcoaceticuswere found to be tens of times lower than in the case of E. coli.The intracellular content of orthophosphates in A. calcoaceticuscells reached 35–77% of the total phosphorus content (P_total), providing for the intense synthesis of polyphosphates. The P_totalof the A. calcoaceticuscells grown in media with different proportions between the concentrations of acetate and phosphorus varied from 0.7 to 3.3%, averaging 2%. This value of P_totalis about two times higher than that observed for fermenting E. colicells. Lowering the cultivation temperature of A. calcoaceticusfrom 37–32 to 4°C augmented the accumulation of orthophosphates in the cytoplasm, presumably owing to a decreased requirement of growth processes for orthophosphate. In this case, if the concentration of phosphates in the cultivation medium was low, they were completely depleted.