Phenotypic characteristics contributing to the enhanced growth of Escherichia coli bloom strains

Abstract

During bloom events,Escherichia colicell countsincrease to between 10,000 and 100,000 cfu/100 mlof water. The strains responsible for bloom eventsbelong toE. coliphylogenetic groups A and B1,and all have acquired a capsule fromKlebsiella.Apan-genome comparison of phylogroup AE. colirevealed that the ferric citrate uptake system(fecIRABCDE) was overrepresented in phylogroupA bloom strains compared with non-bloomE. coli.A series of experiments were carried out to investi-gate if the capsule together with ferric citrateuptake system could confer a growth rate advan-tage onE. coli. Capsulated strains had a growthrate advantage regardless of the media composi-tion and the presence/absence of thefecoperon,and they had a shorter lag phase compared withcapsule-negative strains. The results suggest thattheKlebsiellacapsule may facilitate nutrientuptake or utilization by a strain. This, together withthe protective roles played by the capsule and theshorter lag phase of capsule-positive strains, mayexplain why it is only capsule-positive strains thatproduce elevated counts in response to nutrientinflux. Show more