Stress Tolerance and Environmental Fitness of Pseudomonas fluorescens A506, Which Has a Mutation in rpoS

Abstract

Establishment of suppressive populations of bacterial biological control agents on aerial plant surfaces is a critical phase in biologically based management of floral diseases. Periodically, biocontrol agents encounter inhospitable conditions for growth on plants; consequently, tolerance of environmental stresses may contribute to their fitness. In many gram-negative bacteria, including strains of Pseudomonas spp., the capacity to survive environmental stresses is influenced by the stationary phase sigma factor RpoS. This study focused on the role of RpoS in stress response and epiphytic fitness of Pseudomonas fluorescens A506, a well-studied bacterial biological control agent. We detected a frameshift mutation in the rpoS of A506 and demonstrated that the mutation resulted in a truncated, nonfunctional RpoS. Using site-directed mutagenesis, we deleted a nucleotide from rpoS, which then encoded a full-length, functional RpoS. We compared the stress response and epiphytic fitness of A506 with derivative strains having the functional full-length RpoS or a disrupted, nonfunctional RpoS. RpoS had little effect on stress response of A506 and no consistent influence on epiphytic population size of A506 on pear or apple leaves or flowers. Although the capacity of strain A506 to withstand exposure to environmental stresses was similar to that of other fluorescent pseudomonads, this capacity was largely independent of rpoS.

Transcriptional Analysis of the Global Regulatory Networks Active in Pseudomonas syringae during Leaf Colonization

“…In particular, RpoS influenced only a small number of genes, and the growth of the ∆ rpoS mutant was similar to the growth of the wild type. As observed with Pseudomonas fluorescens A506 (69), RpoS was not a major regulator of environmental stress tolerance in strain B728a. In contrast, AlgU regulated a large number of genes involved in mediating tolerance to water limitation and oxidative stress, and the ∆ algU mutant established populations that were approximately 10-fold lower than those of the wild type on and in leaves (Fig.…”

“…RpoS contributes to the tolerance of a P . protegens strain to stresses, including osmotic and oxidative stresses, desiccation, UV irradiation, freezing, and starvation (21), but it has a much smaller influence (68) or no influence (69) on the stress tolerance of two P. fluorescens strains. This illustrates the potential for differences among pseudomonad strains in the role of RpoS and precedence for little to no role for RpoS in stress tolerance in pseudomonads.…”

Comparative Genomics of Plant-Associated Pseudomonas spp.: Insights into Diversity and Inheritance of Traits Involved in Multitrophic Interactions

“…Strains A506, 30-84, SS101, and BG33R are rifampicin-resistant (100 µg/ml) derivatives of field isolates; previously, spontaneous mutants with resistance to rifampicin were selected to facilitate tracking of these strains in field studies. Strain A506 is known to have a single nucleotide insertion in rpoS , which causes a frameshift resulting in a truncated form of the stationary-phase sigma factor RpoS [140]. During the course of this work, we discovered that strain Pf0-1 has a mutation in gacA , which encodes a component of the GacA/GacS global regulatory system in Pseudomonas spp.…”

Physiological and Transcriptional Responses to Osmotic Stress of Two Pseudomonas syringae Strains That Differ in Epiphytic Fitness and Osmotolerance

“…Similarly, small differences in osmotolerance may reflect subtle differences in osmoadaptation mechanisms, with these differences influencing the relative fitness of individual species and strains. In most terrestrial environments, water stress tolerance is an important component of bacterial fitness and is therefore relevant to understanding, predicting, and manipulating the ecological success of target organisms, such as for biocontrol (1,2). Pseudomonas syringae is a foliar pathogen, as well as a common resident on leaves.…”