Maritime and continental microorganisms collected in Mexico: An investigation of their ice-nucleating abilities

Airborne biological particles have a great potential to affect the hydrological cycle as they have been reported as the most efficient ice nucleating particles (INPs). However, their spatiospatial-temporal variability and their ice nucleation abilities are highly uncertain. The present study reports the ice-nucleating abilities, via immersion freezing, of 32 bacteria, 6 fungi, and 26 marine phytoplankton species isolated in different environments in Mexico. Although 15 of the 56 evaluated microorganisms were found to trigger ice formation at temperatures above-21.5 & DEG;C, 41 species (i.e., 91% of the studied microorganisms) can be considered as inefficient INPs as their median freezing temperatures (T50) were observed to be below-25 & DEG;C. Only the Cupriavidus pauculus and the Phaeocystis sp. reported moderately warm T50 values, i.e.,-17.3 & DEG;C and -19.5 & DEG;C, respectively. This cor-roborates the hypothesis that only a very limited fraction of the bioaerosol population have the potential to impact ice formation within clouds, including those found in the Tropics. Finally, out of the three bioparticles studied, phytoplankton showed to be the most efficient INP, in terms of T50, while fungal propagules show the lowest potential to impact mixed-phase cloud formation because of their poor ice-nucleating abilities.

Automated summary

Airborne biological particles, including bacteria, fungi, and marine phytoplankton, have the potential to impact the hydrological cycle by acting as ice nucleating particles. However, their variability and ice nucleation abilities are uncertain. A study in Mexico found that out of 56 microorganisms tested, 15 triggered ice formation at temperatures above -21.5°C, but the majority of them were considered inefficient INPs with median freezing temperatures below -25°C. Phytoplankton showed the highest ice nucleation ability, while fungal propagules had the lowest potential to impact mixed-phase cloud formation.