Fatty acid starvation activates RelA by depleting lysine precursor pyruvate

Bacteria undergoing nutrient starvation induce the ubiquitous stringent response, resulting in gross physiological changes that reprograms cell metabolism from fast to slow growth. The stringent response is mediated by the secondary messengers pppGpp and ppGpp collectively referred to as (p)ppGpp or 'alarmone'. In Escherichia coli, two paralogs, RelA and SpoT, synthesize (p)ppGpp. RelA is activated by amino acid starvation, whereas SpoT, which can also degrade (p)ppGpp, responds to fatty acid (FA), carbon and phosphate starvation. Here, we discover that FA starvation leads to rapid activation of RelA and reveal the underlying mechanism. We show that FA starvation leads to depletion of lysine that, in turn, leads to the accumulation of uncharged tRNA(Lys) and activation of RelA. SpoT was also activated by FA starvation but to a lower level and with a delayed kinetics. Next, we discovered that pyruvate, a precursor of lysine, is depleted by FA starvation. We also propose a mechanism that explains how FA starvation leads to pyruvate depletion. Together our results raise the possibility that RelA may be a major player under many starvation conditions previously thought to depend principally on SpoT. Interestingly, FA starvation provoked a similar to 100-fold increase in relA dependent ampicillin tolerance

Chitinases from Vibrio: activity screening and purification of chiA from Vibrio carchariae

Fourteen species of Vibrio were screened for chitin-induced chitinase activity in culture medium. V. carchariae, V. alginolyticus 283 and V. campbellii showed high levels of activity. Screening on agar plates containing swollen chitin showed high levels of chitinase activity by the same three species, and also by V. fischeri and V. alginolyticus 284. An affinity purification procedure was developed for the chitinase from V. carchariae. The purified chitinase was active as a monomer with Mr 63 000–66 000, and displayed activity toward polymeric chitin from acetylated chitosan or from crab shells. N-terminal sequence analysis and immunological cross-reactivity confirmed that the enzyme belongs to the group A/chiA family of bacterial chitinases

Co-ordination of Legionella pneumophila virulence with entry into stationary phase by ppGpp

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71832/1/j.1365-2958.1999.01519.x.pd