Lon protease influences antibiotic production and UV tolerance of Pseudomonas fluorescens Pf-5

Pseudomonas fluorescens Pf-5 is a soil bacterium that suppresses plant path ogens due in part to its production of the antibiotic pyoluteorin. Previous characterization of Pf-5 revealed three global regulators, Including the s tationary-phase sigma factor sigma(S) and the two-component regulators GacA and GacS, that influence both antibiotic production and stress response. I n this report, we describe the serine protease Lon as a fourth global regul ator influencing these phenotypes in Pf-5. lan mutants overproduced pyolute orin, transcribed pyoluteorin biosynthesis genes at enhanced levels, and we re more sensitive to UV exposure than Pf-5. The lan gene was preceded by se quences that resembled promoters recognized by the heat shock sigma factor sigma(32) (sigma(H)) of Escherichia call, and Lon accumulation by Pf-5 incr eased after heat shock Therefore, sigma(H) represents the third sigma facto r (with sigma(S) and sigma(70)) implicated in the regulation of antibiotic production by P. fluorescens. Lon protein levels were similar in stationary -phase and exponentially growing cultures of Pf-5 and were not positively a ffected by the global regulator sigma(S) or GacS. The association of antibi otic production and stress response has practical implications for the succ ess of disease suppression in the soil environment, where biological contro l organisms such as Pf-5 are likely to encounter environmental stresses.