The Role of Pigmentation, Ultraviolet Radiation Tolerance, and Leaf Colonization Strategies in the Epiphytic Survival of Phyllosphere Bacteria

Abstract

Phenotypic mechanisms that enhance bacterial UVR survival typically include pigmentation and DNA repair mechanisms which provide protection from UVA and UVB wavelengths, respectively. In this study, we examined the contribution of pigmentation to field survival in Clavibacter michiganensis and evaluated differences in population dynamics and leaf colonization strategies. Two C. michiganensis pigment-deficient mutants were significantly reduced in UVA radiation survival in vitro; one of these mutants also exhibited reduced field populations on peanut when compared to the wild-type strain over the course of replicate 25-day experiments. The UVR-tolerant C. michiganensis strains G7.1 and G11.1 maintained larger epiphytic field populations on peanut compared to the UVR-sensitive C. michiganensis T5.1. Epiphytic field populations of C. michiganensis utilized the strategy of solar UVR avoidance during leaf colonization resulting in increased strain survival on leaves after UVC irradiation. These results further demonstrate the importance of UVR tolerance in the ability of bacterial strains to maintain population size in the phyllosphere. However, an examination of several bacterial species from the peanut phyllosphere and a collection of environmental Pseudomonas spp. revealed that sensitivity to UVA and UVC radiation was correlated in some but not all of these bacteria. These results underscore a need to further understand the biological effects of different solar wavelength groups on microbial ecology.

Comparison of the complete genome sequences of Pseudomonas syringae pv. syringae B728a and pv. tomato DC3000

“…This enzyme allows bacteria to cope with otherwise lethal effects of UV radiation, albeit at the price of an increased mutation rate. Pss B728a is far less sensitive than Pst DC3000 to UV irradiation (19). Analysis of the genes involved in UV and reactive oxygen species (ROS) resistance in Pst DC3000 and Pss B728a (Table 6, which is published as supporting information on the PNAS web site) reveals that they share a number of pathways for detoxification of ROS and DNA repair, including photorepair, base excision repair, and nucleotide excision repair.…”

Role of Microbial Immigration in the Colonization of Apple Leaves by Aureobasidium pullulans

“…Obviously, phytotron and field conditions are different. In the field, microbes on the phylloplane are exposed to fluctuations in sunlight, moisture, temperature, and wind (9,12). The cuticle erodes, which can alter leaf topography, the wettability of the surface, exudation of nutrients, and retention of microbes (5,18,24).…”

pA506, a Conjugative Plasmid of the Plant Epiphyte Pseudomonas fluorescens A506

“…rulAB are known to increase the tolerance of P. syringae strains to UVB and UVC irradiation, which causes DNA damage (67,(69)(70)(71)(72), so we determined if pA506 enhanced UVC tolerance of A506, as expected due to the plasmid-borne rulAB operon. To test the sensitivity of our assay, we compared UVC tolerance of A506 to those of P. fluorescens SS101 and P. brassicacearum Q8r1-96, which have rulAB, and to that of P. chlororaphis O6, which lacks rulAB (6).…”