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Chapter 13 : Growth, Sporulation, and Other Tough Decisions
Many types of bacteria produce dormant spores when faced with nutrient deprivation. The decision to enter the developmental pathway is made when the cell is faced with environmental conditions that are unsuitable for vigorous growth but still possesses the nutritional resources to complete development. During development two significant metabolic events occur. First, carbon limitation forces the cell to reduce the catabolism of organic molecules and redirect the flow of carbon to anabolic pathways. Second, the biosynthetic priority shifts from the synthesis of growth-related macromolecular products, such as chromosomes and ribosomes, to structural components of the spore. The myxobacterium Myxococcus xanthus is an aerobic chemoorganotroph that derives carbon, nitrogen, and energy through catabolism of amino acids. Cell elongation and DNA and stable-RNA synthesis cease in SocE-depleted cells. In Escherichia coli, the stringent response helps regulate the growth rate. When E. coli is starved for amino acids, charged tRNA molecules become limiting and ribosomes pause during elongation. The socE and csgA genes are both regulated by RelA but have opposite transcription patterns during the M. xanthus life cycle. A drop of rain or a gust of wind could disperse a population to densities insufficient to complete fruiting body development. If this occurs after A-signaling, then the decision to resume growth would need to be made promptly and in a different manner.