Quorum‐quenching endophytic bacteria inhibit disease caused byPseudomonas syringaepv. syringae inCitruscultivars

Abstract

Two strains of 64 endophytic bacteria, Bacillus cereus Si‐Ps1 and Pseudomonas azotoformans La‐Pot3‐3, isolated from Citrus sinensis and C. sinensis var. Thomson's leaves, respectively, reduced N‐acyl homoserine‐based quorum sensing in bioindicator strain Pseudomonas syringae pv. syringae (Pss) B728a and the biofilm production and swarming motility of field isolate Pss 3289. A homolog of aiiA gene encoding an AHL‐lactonase was found in B. cereus (Si‐Ps1), suggesting that this isolate can degrade the quorum‐sensing signal molecules of Pss 3289. The crude extract of endophytic bacterium, B. cereus (Si‐Ps1), inhibited Pss 3289 biofilm formation after 48 and 96 h by 55% and 58%, respectively. Similar reductions in biofilm formation were conferred by crude extracts of P. azotoformans (La‐Pot3‐3). Correspondingly, the number of planktonic cells in cultures treated with these extracts was higher than in control cultures, indicating a direct effect on biofilm formation and not on cell growth. In greenhouse assays, the virulence of Pss 3289 to different citrus cultivars was decreased when coinoculated with these endophytic bacteria.

The conserved iol gene cluster in Pseudomonas is involved in rhizosphere competence

“…46 The connection between inositol metabolism, the iol locus, and quorum behavior could explain the decrease in optical density in the Diol CHA0 at the onset of the stationary phase that we observe and, additionally, the enhanced production of siderophores that we observed after 6 days on plates. This is further supported by our results in swarming motility, for which quorum-based coordination is required, 47,48 where inositol does not seem to affect swarming of WT cells, whereas it abolishes swarming in the iol mutant.…”