TREHALOSE INDUCES ANTAGONISM TOWARDS PYTHIUM-DEBARYANUM IN PSEUDOMONAS-FLUORESCENS ATCC-17400

Pseudomonas fluorescens ATCC 17400 shows in vitro activity against Pyt hium debaryanum under conditions of iron limitation. A lacZ reporter g ene introduced by transposon mutagenesis into the P. fluorescens ATCC 17400 trehalase gene (treA) was induced by a factor released by the ph ytopathogen Pythium debaryanum. The induction of the lacZ gene was los t upon treatment of the Pythium supernatant with commercial trehalase. A trehalose concentration as low as I mu M could induce the expressio n of treA. The mutation did not affect the wild-type potential for fun gus antagonism but drastically decreased the osmotolerance of the muta nt in liquid culture and suppressed the ability of P. fluorescens ATCC 17400 to utilize trehalose as a carbon source. A subsequent transposo n insertion in treP, one of the trehalose phosphotransferase genes ups tream of treA, silenced the lacZ gene. This double mutant restricted f ungal growth only under conditions of high osmolarity, which probably results in internal trehalose accumulation. These data confirm the rol e of tile disaccharide trehalose in osmotolerance, and they indicate i ts additional role as an initiator of or a signal for fungal antagonis m.