The success of bacteria in such conditions depends on their ability to sense the nutritional status of the environment and respond appropriately by reprogramming their gene expression and cell metabolism. For instance, nutrient depletion triggers starvation response that involves the stress-specific sigma factor RpoS and results in drastic changes in

gene expression and finally arrests cell growth and division [1]. Bacteria can also discriminate between nutrient-rich and nutrient-poor conditions and respond to nutrient limitation through a regulated nutrient-specific hunger response [2]. Hunger response, activated when the growth rate of a bacterial population decreases due to limited acquisition of nutrients, essentially differs from the starvation response. While the starvation response Poziotinib price prepares a cell population for survival in a nutrient-depleted

environment, the hunger response improves the ability of bacteria to grow under nutrient-poor conditions [3]. The most obvious bacterial physiological response to low nutrient levels is the enhancement of scavenging ability for the limiting nutrient [2, 4]. For instance, if E. coli is cultivated in glucose-limited chemostat, its permeability to glucose is increased through up-regulation of several outer membrane porins and high-affinity cytoplasmic membrane transporters [5–8]. AZD3965 price However, as the rpoS gene was not induced in these conditions, hunger-induced changes should be considered distinct from stationary

phase response [8]. Importantly, the mutants that are defective in some hunger-induced transporter have reduced fitness BVD-523 purchase in nutrient-poor Phosphoprotein phosphatase conditions [5, 9]. Hunger response has been studied by cultivation of bacteria in chemostat which allows a long-term and almost steady-state growth in nutrient-limiting conditions [2]. However, liquid batch cultures of bacteria also transiently experience a nutrient-limited period just before the exhaustion of the carbon source from the medium. Bacteria that grow on solid surfaces, e.g. on agar plates, encounter specific complications of nutrient acquisition, as during consumption of growth substrates niches with different nutrient level develop, which in turn results in a cellular differentiation and an increase in population heterogeneity [10]. The main difference between growth conditions of bacteria in liquid and on solid media is the development of nutrient concentration gradients during the growth on solid medium. This may significantly influence bacterial responses, as has been illustrated by the spatially and temporally different expression of a reporter gene in Bacillus subtilis [11, 12]. Similarly, nutrient gradients that develop in other types of structured multicellular bacterial consortia, e.g. in biofilms, cause considerable physiological heterogeneity [13]. For example, the P.