TABLE 2.

Influence of F. oxysporum culture filtrates on phlA expression in P. fluorescens CHA0 and CHA638^a

P. fluorescens strain	F. oxysporum strain	FA concn in bacterial growth medium (μM)	β-Galactosidase activity (U per 108 CFU)
			OD600 = 1.5	OD600 = 2.5
CHA0	None	0	1,510 a	2,100 a
	240	0	1,520 a	2,000 a
	241	25	1,480 a	1,910 a
	242	0	1,460 a	1,950 a
	410	0	1,640 a	1,920 a
	798	700	220 b	590 b
	801	160	200 b	1,520 c
CHA638	None	0	1,850 a	1,720 a
	240	0	1,660 a	1,390 a
	241	25	1,590 a	1,590 a
	242	0	1,540 a	1,560 a
	410	0	1,740 a	1,680 a
	798	700	1,660 a	1,490 a
	801	160	1,680 a	1,470 a

^aP. fluorescens CHA0 (wild type) and CHA638 (phlF mutant) carrying a translational phlA′-′lacZ fusion on plasmid pME6259 were tested. The F. oxysporum strains were cultivated in Czapek Dox medium for 7 days at 24°C and 180 rpm. Filtrates from F. oxysporum cultures were added to bacterial growth medium OSG at a ratio of 20% (vol/vol). The FA content of the culture filtrates was determined, and the final FA concentration in the bacterial growth medium is indicated. β-Galactosidase activities were determined in bacterial cultures grown to an OD₆₀₀ of 1.5 ± 0.1 or 2.5 ± 0.1, as indicated. Data represent means of three replicate cultures. Means for the same P. fluorescens strain within a column followed by a different letter are significantly different at P ≤ 0.05 according to Fisher's protected least significant difference test.