Effect of Plant Species and Environmental Conditions on Ice Nucleation Activity of Pseudomonas syringae on Leaves

Abstract

Selected plant species and environmental conditions were investigated for their influences on expression of ice nucleation activity by 15 Pseudomonas syringae strains grown on plants in constant-temperature growth chamber studies. Ice nucleation frequencies (INFs), the fraction of cells that expressed ice nucleation at-5 or-9°C, of individual strains varied greatly, both on plants and in culture. This suggests that the probability of frost injury, which is proportional to the number of ice nuclei on leaf surfaces, is strongly determined by the particular bacterial strains that are present on a leaf surface. The INFs of strains were generally higher when they were grown on plants than when they were grown in culture. In addition, INFs in culture did not correlate closely with INFs on plants, suggesting that frost injury prediction should be based on INF measurements of cells grown on plants rather than in culture. The relative INFs of individual strains varied with plant host and environment. However, none of seven plant species tested optimized the INFs of all 15 strains. Similarly, incubation for 48 h at near 100% relative humidity with short photoperiods did not always decrease the INF when compared with a 72 h, 40% relative humidity, long-photoperiod incubation. Pathogenic strains on susceptible hosts were not associated with higher or lower INFs relative to their INFs on nonsusceptible plant species. The ice nucleation activity of individual bacterial strains on plants therefore appears to be controlled by complex and interacting factors such as strain genotype, environment, and host plant species.

A Biological Sensor for Iron Available to Bacteria in Their Habitats on Plant Surfaces

“…Plasmid pSFL12 was mutagenized with Tn3-HoHol by using previously described methods (51). Following matings with E. coli donors harboring pSFL12::Tn3-HoHol, colonies of P. syningae 31R1 that harbored fusion plasmids were selected on medium 925 (20) containing myo-inositol (10 g/liter) as a sole carbon source, tetracycline, ampicillin, and 5-bromo-4-chloro-3-indoyl-p-D-galactopyranoside (X-Gal) (40 ,ug/ml). After 3 days of incubation at 27°C, the colonies were screened for a blue color, which indicated that there was a Tn3-HoHol insertion downstream of a promoter.…”

“…Individual leaflets from trifoliate leaves or individual root systems were placed in a washing buffer (40) and sonicated for 5 min to remove bacterial cells from tissue surfaces or rhizosphere soil. The washing buffer containing suspended bacterial cells was diluted, and bacterial population size was determined by spreading aliquots of dilutions on King's medium B (17) containing rifampin, using previously described methods (33,40). The ice nucleation activities of bacteria inhabiting the rhizosphere or phyllosphere were determined by the dropletfreezing assay (24).…”

“…A genomic region whose transcription was regulated strongly by iron was identified by Tn3-HoHol mutagenesis of plasmid pSFL12 (32), which contains cloned genes involved in pyoverdine biosynthesis (pvd) in P. syringae 31. Colonies of P. syringae 31R1 containing pSFL12 with random insertions of Tn3-HoHol were evaluated for 3-galactosidase activity. We identified 40 colonies that were blue on medium 925 containing X-Gal but were white on medium 925 containing X-Gal and 10-4 M FeCl3. Plasmid pJEL1395, which was isolated from one of the 40 colonies, did not confer ,-galactosidase activity on E. coli DH5o or HB1O1.…”

Biogenic ice nuclei in boundary layer air over two U.S. High Plains agricultural regions

“…Because the large aggregates are labile, a variable and typically small fraction of all cells will possess activity at these warm temperatures. For example, O'Brien and Lindow [1988] observed the fraction of INA P. syringae strains grown on plants able to nucleate at −5°C to range from 1 in 30 to 1 in 20,000 for a variety of experimental conditions. At colder temperatures clusters of a few proteins are enough to trigger freezing, so that by −10°C to −12°C the nucleation frequency may be 1 in 10 cells or higher [ Hirano and Upper , 2000; Kim et al , 1987]; a single Ina protein nucleates at −12 to −13°C [ Govindarajan and Lindow , 1988].…”

Microbiology and atmospheric processes: biological, physical and chemical characterization of aerosol particles

“…Even if the gene responsible for this property is present in the genome, bacterial ice nucleation is not always fully expressed. Nutritional and environmental factors influence this expression and the subsequent ice nucleation activity of the bacterium (O'Brien et al, 1988;Nemecek-Marshall et al, 1993). It is not known if such variability exists in other organisms with ice nucleation activity.…”