title: Activation of the cryptic PhnE permease promotes rapid adaptive evolution in a population of Escherichia coli K-12 starved for phosphate.
abstract: Escherichia coli K-12 suffers acetic acid stress during prolonged incubation in glucose minimal medium containing a limiting concentration of inorganic phosphate (0.1 mM P(i)), which decreases the number of viable cells from 6 × 10(8) to ≤10 CFU/ml between days 6 and 14 of incubation. Here we show that following two serial transfers into P(i)-limiting medium, evolved mutants survived prolonged incubation (≈10(7) CFU/ml on day 14 of incubation). The evolved strains that overtook the populations were generally PhnE(+), whereas the ancestral K-12 strain carries an inactive phnE allele, which prevents the transport of phosphonates. The switching in phnE occurred with a high frequency as a result of the deletion of an 8-bp repeated sequence. In a mixed culture starved for P(i) that contained the K-12 ancestral strain in majority, evolved strains grew through PhnE-dependent scavenging of probably organic phosphate esters (not phosphonates or P(i)) released by E. coli K-12 between days 1 and 3, before acetic acid excreted by E. coli K-12 reached toxic levels. The growth yield of phnE(+) strains in mixed culture was dramatically enhanced by mutations that affect glucose metabolism, such as an rpoS mutation inactivating the alternative sigma factor RpoS. The long-term viability of evolved populations was generally higher when the ancestral strain carried an inactive rather than an active phnE allele, which indicates that cross-feeding of phosphorylated products as a result of the phnE polymorphism may be essential for the spread of mutants which eventually help populations to survive under P(i) starvation conditions.
authors: Laboratoire de Chimie Bactérienne, Centre National de la Recherche Scientifique, Aix-Marseille University, Marseille, France.
authors: Mélanie L
authors: ML
authors: Guillemet
authors: Patrice L
authors: PL
authors: Moreau
mesh_terms: D027321:Anion Transport Proteins / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D005075:Biological Evolution; D004789:Enzyme Activation; D048168:Escherichia coli K12 / Q000201:enzymology* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D010755:Organophosphates; D010641:Phenotype; D010710:Phosphates / Q000378:metabolism*; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism
chemical_list: D027321:Anion Transport Proteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D010755:Organophosphates; C570408:PhnE protein, E coli; D010710:Phosphates; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria