Pseudomonas fluorescens Pf0-1 exhibited chemotactic responses to
l-malate, succinate, and fumarate. We constructed a plasmid library of 37 methyl-accepting chemotaxis protein (MCP) genes of
P. fluorescens Pf0-1. To identify a MCP for
l-malate, the plasmid library was screened using the PA2652 mutant of
Pseudomonas aeruginosa PAO1, a mutant defective in chemotaxis to
l-malate. The introduction of Pfl01_0728 and Pfl01_3768 genes restored the ability of the PA2652 mutant to respond to
l-malate. The Pfl01_0728 and Pfl01_3768 double mutant of
P. fluorescens Pf0-1 showed no response to
l-malate or succinate, while the Pfl01_0728 single mutant did not respond to fumarate. These results indicated that Pfl01_0728 and Pfl01_3768 were the major MCPs for
l-malate and succinate, and Pfl01_0728 was also a major MCP for fumarate. The Pfl01_0728 and Pfl01_3768 double mutant unexpectedly exhibited stronger responses toward the tomato root exudate and amino acids such as proline, asparagine, methionine, and phenylalanine than those of the wild-type strain. The
ctaA,
ctaB,
ctaC (genes of the major MCPs for amino acids), Pfl01_0728, and Pfl01_3768 quintuple mutant of
P. fluorescens Pf0-1 was less competitive than the
ctaA ctaB ctaC triple mutant in competitive root colonization, suggesting that chemotaxis to
l-malate, succinate, and/or fumarate was involved in tomato root colonization by
P. fluorescens Pf0-1.
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