Diversity and Abundance of Ice Nucleating Strains ofPseudomonas syringaein a Freshwater Lake in Virginia, USA.
The bacteriumPseudomonas syringaeis found in a variety of terrestrial and aquatic environments. Some strains ofP. syringaeexpress an ice nucleation protein (hereafter referred to as Ice+) allowing them to catalyze the heterogeneous freezing of water. ThoughP. syringaehas been sampled intensively from freshwater sources in France, little is known about the genetic diversity ofP. syringaein natural aquatic habitats in North America. We collected samples of freshwater from three different depths in Claytor Lake, Virginia, USA between November 2015 and June 2016. Samples were plated on non-selective medium (TSA) and on medium selective forPseudomonas(KBC) and closely related species to estimate the total number of culturable bacteria and ofPseudomonas, respectively. A droplet freezing assay was used to screen colonies for the Ice+ phenotype. Ice+ colonies were then molecularly identified based on thects(citrate synthase) gene and the 16S rDNA gene. Phylogenetic analysis ofctssequences showed a surprising diversity of phylogenetic subgroups ofP. syringae. Frequencies of Ice+ isolates onP. syringaeselective medium ranged from 0 to 15% per sample with the highest frequency being found in spring. Our work shows that freshwater lakes can be a significant reservoir of Ice+P. syringae. Future work is needed to determine the contribution ofP. syringaefrom freshwater lakes to theP. syringaepopulations present in the atmosphere and on plants and, in particular, if freshwater lakes could be an inoculum source ofP. syringae-caused plant disease outbreaks.
Department of Biological Sciences, Virginia Tech Blacksburg, VA, USA.
Renée B
RB
Pietsch
Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech Blacksburg, VA, USA.
Boris A
BA
Vinatzer
Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech Blacksburg, VA, USA.
David G
DG
Schmale
Pseudomonas; Pseudomonas syringae; cts; freshwater bacteria; ice nucleation