High-level expression of ice nuclei in a Pseudomonas syringae strain is induced by nutrient limitation and low temperature

Abstract

Attempts were made to maximize the expression of ice nuclei in Pseudomonas syringae Ti isolated from a tomato leaf. Nutritional starvation for nitrogen, phosphorous, sulfur, or iron but not carbon at 320C, coupled to a shift to 14 to 18'C, led to the rapid induction of type 1 ice nuclei (i.e., ice nuclei active at temperatures warmer than -50C nuclei and the number of bacterial cells in a culture (i.e., ice nucleation frequency) varied with incubation temperature, growth medium composition, culture age, and genotype. Hirano et al. (9) showed that culturing of different Pseudomonas syringae strains under identical conditions results in ice nucleation frequencies at a given temperature, such as -50C, that vary from one in 100 cells to as few as one in 106 cells. The basis for this variability is unknown. Enhanced expression of ice nuclei, especially type 1 nuclei, has been noted for P. syringae cultures grown at 20 to 240C on nutrient agar containing glycerol (22); optimal conditions increased -50C ice nuclei from 1 in 410,000 to 1 in 72 cells. Using a chemically defined medium, Pooley and Brown (31) similarly noted enhanced ice nucleation frequencies and elevated threshold ice nucleation temperatures for cultures of P. syringae grown on solid versus liquid media. For submerged cultures of P. syringae, Pooley and Brown found that the highest threshold ice nucleation temperatures and frequencies were achieved in mid-to late-log-phase cultures grown in a chemically defined medium rather than a complex growth medium. They suggested that components within the complex medium may have inhibitory effects on the expression of ice nuclei, which is maximal late in the growth cycle. Programmed fermentations designed to achieve maximal cell densities and ice nucleation frequencies have taken advantage of this correlation between the temporal expression of ice nuclei in the cell cycle and nutritional growth requirements (18). In this work, maximal ice nucleation frequencies at -50C, approaching one active nucleus in 10 cells to one in every cell in the population, were achieved for submerged cultures of P. syringae. This result was accomplished by supplying stoichiometrically limiting quantities of nitrogen 4062 on May 9, 2018 by guest

Atmospheric ice nucleators active ≥ −12 °C can be quantified on PM<sub>10</sub> filters

“…Another potential disadvantage of retrospectively selecting PM 10 filters for analysis is that IN properties may change during filter storage. Living Pseudomonas syringae, for example, change their IN activity within hours, depending on temperature and nutrient status (Nemecek-Marshall et al, 1993). IN active sites in organisms are proteins (Wolber et al, 1986;Morris et al, 2004).…”

Spatial variability in airborne bacterial communities across land-use types and their relationship to the bacterial communities of potential source environments

“…Bacterial abundances are reported as the number of cells per m 3 of air, taking into account the dilution and the volume of air that passed through each filter. For ice nucleation assays, particles were removed from the filters using the same protocol described above, except that the filters were shaken at 4 1C instead of room temperature to minimize warming, which may alter the ice nucleating capabilities of bacterial cells (Nemecek-Marshall et al, 1993). Drop-freeze assays were performed using a protocol described previously (Bowers et al, 2009), which was modified from a protocol described in Vali (1971).…”

Enhanced production of extracellular ice nucleators from Erwinia herbicola.

“…On the hand, Pooley and Brown (1991) found that large numbers of ice nuclei from P. syringae 1105 were obtained by using Koser citrate broth. Nemecek-Marshall et al (1993) reported that nutrient limitation and low temperature induced high levels of ice nuclei by P. syringae T1. Phosphate starvation and low temperature also induced a high-level expression of ice nuclei in E. herbicola (Fall and Fall, 1998).…”