Unbalanced growth:
An unusual characteristic of the Bdellovibrio growth cycle is its unbalanced growth. This occurs during the intraperiplasmic replication and is in reference to the proportions of DNA and cell volume.
Gray (et al, 1989) found that the rate of DNA replication and protein synthesis were both exponential in the filamentous cell, but DNA was synthesized at a greater rate. They also found that the number of chromosomal origins per unit cell mass was not constant, but actually increased with each round of replication. Likewise, it was concluded that there must also be multiple elongation sites along the filamentous wall for exponential increase of cell mass. The original ratio of DNA:protein was only restored when protein synthesis was given time to recover after the septation period, when DNA replication has been terminated.
A few ideas have been suggested as to why the DNA and protein growth rates are not coordinated. Gray suggested that it is perhaps an adaptation to produce the maximum progeny possible from the determinant amount of substrate available, and so the minimum sustainable cell mass is maintained. Alternately, it was suggested that the attack phase is already larger in mass than the necessary "initiation volume" for replication, and so DNA synthesis is uncoupled from cell volume |
