Application of models for envelope growth to cell length distribution data for Pseudomonas aeruginosa at various...

Cell length distributions were determined for magnesium-limited steady-state populations of Pseudomonas aeruginosa grown in a chemostat at a variety of specific growth rates (0.037-0.621 h-1). The data were subjected to numerical analysis using an iterative procedure based upon the Collins and Richmond (1962) equation and various models for envelope growth. The cell length distributions of cultures growing at specific growth rates in excess of 0.276 h-1 could be modelled assuming constancy of the rate of increase in cell length, and the Zaritsky-Pritchard (1973) step growth model. Cultures growing at microns less than 0.276 h-1 had length distributions which skewed markedly towards the shorter length cells, and were not consistent with either linear, exponential nor step growth models. Pierucci (1978), however, proposed a model of linear envelope growth, which for slowly growing cultures predicted periods without envelope synthesis at the beginning of each division cycle. Application of such a model for slowly growing cultures produced similar skews in the cell length distributions, but could only adequately model the data when the periods of no-growth occurred in mid-cycle.