Ice-nucleating proteins are activated by low temperatures to control the structure of interfacial water

Ice-nucleation active (INA) bacteria can promote the growth of ice more effectively than any other known material. Using specialized ice-nucleating proteins (INPs), they obtain nutrients from plants by inducing frost damage and, when airborne in the atmosphere, they drive ice nucleation within clouds, which may affect global precipitation patterns. Despite their evident environmental importance, the molecular mechanisms behind INP-induced freezing have remained largely elusive. We investigate the structural basis for the interactions between water and the ice-nucleating protein InaZ from the INA bacterium Pseudomonas syringae. Using vibrational sum-frequency generation (SFG) and two-dimensional infrared spectroscopy, we demonstrate that the ice-active repeats of InaZ adopt a β-helical structure in solution and at water surfaces. In this configuration, interaction between INPs and water molecules imposes structural ordering on the adjacent water network. The observed order of water increases as the interface is cooled to temperatures close to the melting point of water. Experimental SFG data combined with molecular-dynamics simulations and spectral calculations show that InaZ reorients at lower temperatures. This reorientation can enhance water interactions, and thereby the effectiveness of ice nucleation.

JENIS DAN POPULASI BAKTERI ICE NUCLEATION ACTIVE PENYEBAB LUKA BEKU PADA DAUN JERUK KEPROK SOE DI DATARAN TINGGI MUTIS

Research on ice nucleation-active bacteria causes frost injury from tropic areas has not been widely publicized. The purpose of this study was to determine the population of Ice Nucleation-Active Bacteria on Soe tangerines leaves and the class of Ice Nucleation-Active bacteria based on Ice formation temperatures. The collecting of Soe tangerine leaves used the purpose sampling method. Leaves with frost blotches were collected from three stages at altitudes of 1500, 1800, and 2000 meters above sea level (m asl). Bacterial isolation was carried out by the spread plate method on Nutrien Agar 2,5 % glycerol (NAG) media. Ice Nucleation activity was determined by the tube nucleation test method. Estimation of INA bacterial population was conducted by the multiple-tube nucleation test with Thomas series .3.3.3. The result showed that the highest INA bacterial population was 6.9x104 which was found in leaves samples collected from stations 1800 and 2000 m asl, and the lowest population i.e. 5,4x103 on leaf samples from station 1500 m asl. Based on the temperature of ice formation, it was known that INA bacteria that attack the Soe tangerines leaves Mutis plateau are the INA bacteria class B and C.

Presence of ice-nucleating Pseudomonas on wheat leaves promotes Septoria tritici blotch disease (Zymoseptoria tritici) via a mutually beneficial interaction

Zymoseptoria tritici causes Septoria tritici blotch (STB) of wheat, an economically important disease causing yield losses of up to 10% despite the use of fungicides and resistant cultivars. Z. tritici infection is symptomless for around 10 days, during which time the fungus grows randomly across the leaf surface prior to entry through stomata. Wounded leaves show faster, more extensive STB, suggesting that wounds facilitate fungal entry. Wheat leaves also host epiphytic bacteria; these include ice-nucleating (INA+) bacteria, which induce frost damage at warmer temperatures than it otherwise occurs. Here, STB is shown to be more rapid and severe when wheat is exposed to both INA+ bacteria and sub-zero temperatures. This suggests that ice-nucleation-induced wounding of the wheat leaf provides additional openings for fungal entry. INA+ bacterial populations are shown to benefit from the presence of Z. tritici, indicating that this microbial interaction is mutualistic. Finally, control of INA+ bacteria is shown to reduce STB.

The Ice Nucleating Protein InaZ is Activated by Low Temperature

Ice-nucleation active (INA) bacteria can promote the growth of ice more effectively than any other known material. Utilizing specialized ice-nucleating proteins (INPros), they obtain nutrients from plants by inducing frost damage and, when airborne in the atmosphere, they drive ice nucleation within clouds and may affect global precipitation patterns. Despite their evident environmental importance, the molecular mechanisms behind INPro-induced freezing have remained largely elusive. In the present study, we investigated the folding and the structural basis for interactions between water and the ice-nucleating protein InaZ from the INA bacterium Pseudomonas syringae strain R10.79. Using vibrational sum-frequency generation and two-dimensional infrared spectroscopy, we demonstrate that the ice-active repeats of InaZ adopt a β-helical structure in solution and at water surfaces. In this configuration, hydrogen bonding between INPros and water molecules imposes structural ordering on the adjacent water network. The observed order of water increases as the interface is cooled to temperatures close to the melting point of water. Experimental SFG data combined with spectral calculations and molecular-dynamics simulations shows that the INPro reorients at lower temperatures. We suggest that the reorientation can enhance order-inducing water interactions and, thereby, the effectiveness of ice nucleation by InaZ.

Measurement of Ice Nucleation-Active Bacteria on Plants and in Precipitation by Quantitative PCR

ABSTRACTIce nucleation-active (INA) bacteria may function as high-temperature ice-nucleating particles (INP) in clouds, but their effective contribution to atmospheric processes, i.e., their potential to trigger glaciation and precipitation, remains uncertain. We know little about their abundance on natural vegetation, factors that trigger their release, or persistence of their ice nucleation activity once airborne. To facilitate these investigations, we developed two quantitative PCR (qPCR) tests of theinagene to directly count INA bacteria in environmental samples. Each of two primer pairs amplified most alleles of theinagene and, taken together, they should amplify all known alleles. To aid primer design, we collected many new INA isolates. Alignment of their partialinasequences revealed new and deeply branching clades, including sequences fromPseudomonas syringaepv.atropurpurea,Ps. viridiflava,Pantoea agglomerans,Xanthomonas campestris, and possiblyPs. putida,Ps. auricularis, andPs. poae. qPCR of leaf washings recorded ∼108inagenes g−1fresh weight of foliage on cereals and 105to 107g−1on broadleaf crops. Much lower populations were found on most naturally occurring vegetation. In fresh snow,inagenes from various INA bacteria were detected in about half the samples but at abundances that could have accounted for only a minor proportion of INP at −10°C (assuming oneinagene per INA bacterium). Despite this, an apparent biological source contributed an average of ∼85% of INP active at −10°C in snow samples. In contrast, a thunderstorm hail sample contained 0.3 INA bacteria per INP active at −10°C, suggesting a significant contribution to this sample.

Impacts from ice-nucleating bacteria on deep convection: implications for the biosphere-atmosphere interaction in climate change

A cloud modeling framework is described to simulate ice nucleation by biogenic aerosol particles, as represented by airborne ice-nucleation active (INA) bacteria. It includes the empirical parameterization of heterogeneous ice nucleation. The formation of cloud liquid by soluble material coated on such insoluble aerosols is represented and determines their partial removal from deep convective clouds by accretion onto precipitation. Preliminary simulations are performed for a case of deep convection over Oklahoma. If present at high enough concentrations, as might occur in proximity to land sources, INA bacteria are found to influence significantly: – (1) the average numbers and sizes of crystals in the clouds; (2) the horizontal cloud coverage in the free troposphere; and (3) precipitation and incident solar insolation at the surface, which influence rates of bacterial growth. At lower concentrations, the corresponding responses of cloud fields appear much lower or are ambiguous. In nature, the growth rates of INA bacteria on leaves prior to emission into the atmosphere are known to be highly dependent on temperature, precipitation and plant species. Consequently, the open question emerges of whether emissions of such ice-nucleating biogenic particles can then be modified by their own effects on clouds and atmospheric conditions, forming a weak feedback in climate or microclimate systems.