MicrobiologyBytes

A fundamental characteristic of living cells is their ability to regulate growth in response to changing environmental conditions. This review focuses on recent progress toward understanding the mechanisms by which bacterial growth is regulated. These phenomena include the ‘viable but not culturable’ (VBNC) state, in which bacterial growth becomes conditional, and ‘persistence’, which confers antibiotic resistance to a small fraction of bacteria in a population. Notably, at least one form of persistence appears to involve the generation of nongrowing phenotypic variants after transition through stationary phase. The possible roles of toxin-antitoxin modules in growth control are explored, as well as other mechanisms including contact-dependent growth inhibition, which regulates cellular metabolism and growth through binding to an outer membrane protein receptor.

This review focuses on recent advances in our understanding of bacterial growth regulation, with an emphasis on the mechanisms that control entry and exit from a slow growth or nongrowth (dormant) state, excluding spore formation. This topic has relevance to a number of important aspects of bacterial biology including resistance of a small fraction of a bacterial population to killing by an antibiotic, termed “persistence”. The maintenance of bacterial viability without growth impacts human health in a number of ways including maintenance of pathogen reservoirs and chronic infections such as tuberculosis and melioidosis. This has been a difficult area of research, in part due to phenotypic variability in which only a small fraction of bacteria are within a dormant state in a population, making it hard to isolate and study dormant cells. Moreover, since many genes influence cell growth, it has been a challenge to identify those that constitute specific pathway(s) for dormancy/antibiotic resistance. The aim of this review is to delineate some of the key findings and concepts in growth control, bringing together new developments in different fields of research that may impinge on one another.

Signals of growth regulation in bacteria. Curr Opin Microbiol. Oct 22 2009

Related:

• Metabolism, cell growth and the bacterial cell cycle
• How smart are bacteria?

The life of a bacterial cell is feast or famine. To survive the bacterium must rapidly adapt to changing environmental conditions. Colonization of the mammalian gut provides an enteric organism with an abundant source of carbohydrates, whereas a flash flood instantly depletes the nutrient supply for a soil bacterium. Nutrient-rich conditions lead to a decrease in mass doubling time and an increase in cell size, whereas nutrient-poor conditions curtail growth and reduce cell size. Changes in growth rate must be accompanied by changes in the cell cycle to ensure that cell division stays coordinated with mass doubling, chromosome replication and chromosome segregation. How organisms adjust their cell cycle dynamics to compensate for changes in nutritional conditions is an important outstanding question in bacterial physiology. Recent work suggests that multiple signalling pathways transmit nutritional and growth rate information directly to the cell cycle machinery. Multiple signalling pathways permit cells to constantly sample their environments and fine-tune cell cycle processes, a substantial advantage under challenging conditions.

Adaptation to fluctuations in nutrient availability is a fact of life for single-celled organisms in the ‘wild’. A decade ago our understanding of how bacteria adjust cell cycle parameters to accommodate changes in nutrient availability stemmed almost entirely from elegant physiological studies completed in the 1960s. This article summarizes recent groundbreaking work in this area and discuss potential mechanisms by which nutrient availability and metabolic status are coordinated with cell growth, chromosome replication and cell division.

Metabolism, cell growth and the bacterial cell cycle. Nature Reviews Microbiology 7, 822 (2009)

Related:

• Bacterial Chemoreceptors
• A day in the life of a cyanobacterium
• How smart are bacteria?