ON MICROBIAL STATES OF GROWTH

It is crucial to the reproducibility of results and their proper inter pretation that the conditions under which experiments are carried out be defined with rigour and consistency. In this review we attempt to c larify the differences and interrelationships among steady, balanced a nd exponential states of culture growth. Basic thermodynamic concepts are used to introduce the idea of steady-state growth in open, biologi cal systems, The classical, sometimes conflicting, definitions of stea dy-state and balanced growth are presented, and a consistent terminolo gy is proposed, The conditions under which a culture in balanced growt h is also in exponential growth and in steady-state growth are indicat ed. It is pointed out that steady-state growth always implies both bal anced and exponential growth, and examples in which the converse does not hold are described. More complex situations are then characterized and the terminology extended accordingly. This leads to the notion of normal growth and growth that can be synchronous or otherwise unbalan ced but still reproducible, and to the condition of approximate steady state manifested by growth in batch culture and by asymmetrically div iding cells, which is analysed in some detail.