Analysis of bacterial DNA patterns--an approach for controlling biotechnological processes

Optimisation of biotechnological processes catalysed by microbial cells requires detailed information about operational limits of the single cells. Their performance is correlated with distinct physiological states. We related these states to cell cycle events, which were found to proceed extremely diversely in different bacterial strains. Characteristic DNA patterns were found flow cytometrically, depending on the type of strain, substrates and growth conditions involved; this information can be used for the development of control strategies of bioprocesses, although some skill is required. Four bacterial strains (the Gram-negative strains Acinetobacter calcoaceticus 69-V, Ralstonia eutropha JMP 134, Ochrobactrum anthropi K2-14 and the Gram-positive strain Rhodococcus erythropolis K2-3) were grown in mono- and mixed cultures on different substrates, and analysed regarding their proliferation behaviour. The resulting DNA distribution patterns provided three types of valuable information. First, correlation of proliferation activity with the appearance of a major part of cells within the C(2) stage of the cell cycle is a strain-specific feature. Second, bacteria usually maintain more than one chromosome under limiting growth conditions: DNA replication is completed in such cases, but cell division fails. Third, high growth rates are associated with uncoupled DNA synthesis. Its general initiation might be genetically determined in the first place, but it is promoted by optimal growth conditions and the presence of substrates that can be metabolised at high rates, thereby allowing substantial amounts of carbon, other nutrients and energy to be used exclusively for DNA synthesis.