Revisiting the stringent response, ppGpp and starvation signaling

Microbial adaptation to environmental stress plays an important role in sur vival. It is necessary to understand the mechanisms underlying the survival of microbes under stress, as they may eventually aid in the successful con trol of the growth and persistence of these organisms. During nutrient star vation, Escherichia coli elicits a stringent response to conserve energy. T he hallmark of the stringent response is the accumulation of guanosine tetr a-(ppGpp) and pentaphosphates (pppGpp), which probably bind RNA polymerase to regulate gene expression at certain promoters, Recently, there has been renewed interest in the stringent responses of other microbes, with a view to correlating! it with sporulation, virulence and long-term persistence.