On microbial states of growth^†

Abstract

It is crucial to the reproducibility of results and their proper interpretation that the conditions under which experiments are carried out be defined with rigour and consistency. In this review we attempt to clarify the differences and interrelationships among steady, balanced and exponential states of culture growth. Basic thermodynamic concepts are used to introduce the idea of steady-state growth in open, biological systems. The classical, sometimes conflicting, definitions of steady-state and balanced growth are presented, and a consistent terminology is proposed. The conditions under which a culture in balanced growth is also in exponential growth and in steady-state growth are indicated. It is pointed out that steady-state growth always implies both balanced 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 unbalanced but still reproducible, and to the condition of approximate steady state manifested by growth in batch culture and by asymmetrically dividing cells, which is analysed in some detail.

Visualizing multiple constrictions in spheroidal Escherichia coli cells

“…Similar results are obtained by applying penicillin derivatives that specifically interact with PBPs [1]. In all these cases, however, the cultures cannot be maintained in a steady-state of exponential growth [10] and the cells eventually stop dividing and sometimes even lyse at the restrictive conditions.…”

“…The OD 450 was measured with a spectrophotometer (LKB Ultraspec II), and cell numbers with an electronic particle counter (30 µm orifice). Balanced cultures were grown 'normally' [10] for at least 10 doublings by successive dilutions (OD 450 < 0.4).…”

Compaction of the Escherichia coli nucleoid caused by Cyt1Aa

“…Samples of steady-state exponentially growing cultures (Fishov et al, 1995) were fixed (0?25 % formaldehyde) and immobilized on agarose slides as described by Van Helvoort & Woldringh (1994). Prior to immobilization, the samples were stained with DAPI for visualizing nucleoids and their states by combined fluorescence and phase-contrast microscopy (ZEISS Axioplan 2 fluorescence microscope, equipped with Plan-Neofluar 1006/1?3 oil immersion lens and SPOT2 cooled CCD camera; Diagnostic Instruments).…”

“…A steady-state exponentially growing culture of cells (Fishov et al, 1995) harbouring pRM4-C (carrying cyt1Aa) was split into two flasks; CAM (100 mg ml 21 ) was added to one (either with or without 10 mg nalidixic acid ml 21 ) and IPTG (0?5 mM) was added to the other. Compaction of DAPI-stained nucleoids was measured at different times using combined phase-contrast fluorescence micrographs, from which mean relative nucleoid length was calculated.…”

Perpendicular planes of FtsZ arcs in spheroidal Escherichia coli cells

“…The following chemicals were simultaneously added to a culture of LMC1492, grown under 'balanced growth' conditions [12] in rich trypton-yeast medium containing low (though undefined) concentration of thymine: mecillinam (10 µg mL -1 ), to affect rod-sphere transition; L-arabinose (0.2%), to induce ftsZ-gfp; thymine (20 µg mL -1 ) and deoxyguanosine (100 µg mL -1 ), to enhance the rate of chromosome replication hence, temporarily, the frequency of division signals. At 80-100 min, the cells were washed to release the division inhibition by mecillinam, and re-suspended in glucose salts medium without the required amino acids (but with the same concentrations of L-arabinose, thymine and deoxyguanosine) to Pas et al…”