TABLE 4.

Influence of fusaric acid on antibiotic production by Pseudomonas protegens Pf-5^a

Antibiotic	Concn, μg ml−1 (mean ± SE) inb:
	NYBGly-Zn		PDB-Fe
	Without FA	With FA	Without FA	With FA
DAPG	9.8 ± 0.9	0.06 ± 0.02**	2.2 ± 0.3	0.56 ± 0.13**
MAPG	6.6 ± 0.9	0.07 ± 0.03**	15 ± 1	0.93 ± 0.05**
Orfamide A	95 ± 9	78 ± 11	15 ± 1	18 ± 1*
Pyoluteorin	0.87 ± 0.04	1.4 ± 0.1**	BD	0.02 ± 0.01
Pyrrolnitrin	0.36 ± 0.06	0.31 ± 0.06	1.2 ± 0.1	1.4 ± 0.1*

^aStrain Pf-5 was grown in 5 ml of NYBGly supplemented with 0.35 mM zinc sulfate (NYBGly-Zn) or in 5 ml of PDB with 0.1 mM FeCl₃ (PDB-Fe). Both media were amended with fusaric acid (FA) at 0 or 0.5 mM. Cultures were incubated for 48 h at 27°C with shaking at 200 rpm. Prior to extraction, culture supernatants were acidified to pH 2.0, which enhances extraction of some antibiotics but causes degradation of rhizoxin (6, 55). Consequently, rhizoxin WF-1360F concentrations were not assessed in this experiment. Concentrations of antibiotics listed were quantified by HPLC.

^bValues represent the mean and standard error for four replicate broth cultures. Values were rounded to two significant digits. BD, below detection, with detection limits being approximately 0.02 μg/ml for all compounds. For each medium, asterisks (* and **) in the same row indicate values that are significantly different from the control value (α = 0.05 and 0.01, respectively) according to Student's t test.