Microbial Growth under Limiting Conditions-Future Perspectives

Abstract

Microorganisms rule the functioning of our planet and each one of the individual macroscopic living creature. Nevertheless, microbial activity and growth status have always been challenging tasks to determine both in situ and in vivo. Microbial activity is generally related to growth, and the growth rate is a result of the availability of nutrients under adequate or adverse conditions faced by microbial cells in a changing environment. Most studies on microorganisms have been carried out under optimum or near-optimum growth conditions, but scarce information is available about microorganisms at slow-growing states (i.e., near-zero growth and maintenance metabolism). This study aims to better understand microorganisms under growth-limiting conditions. This is expected to provide new perspectives on the functions and relevance of the microbial world. This is because (i) microorganisms in nature frequently face conditions of severe growth limitation, (ii) microorganisms activate singular pathways (mostly genes remaining to be functionally annotated), resulting in a broad range of secondary metabolites, and (iii) the response of microorganisms to slow-growth conditions remains to be understood, including persistence strategies, gene expression, and cell differentiation both within clonal populations and due to the complexity of the environment.

Keywords: continuous culture; growth rate; microbial diversity; microbial growth; near-zero growth; physiological states; stationary phase.

Figure 1

A typical growth curve for a mono-specific microbial culture in batch showing the distinctive phases of growth with incubation time. IP, inflection point; μ_max, maximum growth rate. Abundance, blue line; growth rate, red line; dashed green lines, distinct GASP phenotypes.

Figure 2

Growth rate and relevant parameters during a continuous culturing system in a chemostat. Dilution rate, in logarithmic scale, strictly determines growth rate in a chemostat. Beyond the point when the dilution rate exceeds the maximum growth rate, a wash out of cells occurs. Biomass, blue line; growth rate, red line.

Figure 3

Representation of the biomass and growth rate over time in a retentostat culturing system (with complete biomass retention) for a model microorganism. The progressive increase in biomass (blue line) over time follows a logarithmic curve model, which is used to estimate the actual growth rate (red line) of the cells at a given time point.