冰核细菌Pseudomonas syringae是否可以影响大气的冰核核化过程

Do ice nucleation active bacteria effect on ice nucleation in the real atmosphere: Pseudomonas syringae

近年来,大量的研究表明:生物气溶胶作为有效云凝结核与冰核在大气物理和化学过程中发挥着重要的作用.环境大气和云水样品中,冰核活性细菌Pseudomonas syringae的可培养菌株已经成功地被分离筛选出来.其在大气云物理过程尤其是降水过程中的重要作用也已经成为当前国际大气生物气溶胶气候效应研究的热点.本研究采用液滴冻结实验技术,测试了当前已被确定含有冰核活性菌的3种菌属即假单胞菌属(Pseudomonas)、欧文氏菌属(Erwinia)和黄单胞菌属(Xanthomonas)的代表性标准菌株(P.fluorescen,E.uredovora,X.campestris和P.syringaepv.panici),和被证实具有冰核活性的细菌菌株(P.syringaepv.lachrymans)的菌悬液液滴的冻结温度.结果显示:所测试的目前国际公认的冰核活性细菌属的标准菌株P.syringaepv.panici,P.fluorescen,E.uredovora,和X.campestris并不具备冰核活性,被测细菌菌悬液(OD600=0.25,数浓度108cells/mL)的液滴冻结温度分别是:20.3±2.3℃,21.8±2.3℃,20.8±3.4℃和19.9±3.3℃,与超纯水液滴的冻结温度(20.8±2.7℃)差异不大;而相同浓度下,P.syringaepv.lachrymans(ps1-10)菌株的冻结温度是5.0±0.8℃,具有显著的冰核活性.ps1-10菌株液滴平均冻结温度随着菌悬液浓度梯度降低的变化特征表明,当菌液浓度低于105cells/mL时,菌液液滴冻结温度明显降低,当菌液浓度低于104cells/mL时,菌液液滴与无冰核活性的液滴冻结温度接近.由此本文提出疑问:冰核细菌P.syringae是否能以浸润核化活性在大气真实环境中的冰核异质核化过程中起到重要作用,还是存在其他的作用机制?

In recent years, numerous investigations have highlighted the importance of bioaerosols in the atmosphere as effective cloud condensation nuclei （CCN） or ice nuclei （IN） during atmospheric physics and chemistry processes. Culturable strains of the ice nuclei active （INA） bacteria Pseudomonas syringae have been isolated from cloud water samples. This has led to an increase in research on bioaerosols associated with climatic effects. Such research is important because of the impacts that bacteria have in certain atmospheric cloud physical processes, especially in precipitation processes. This paper reports freezing temperatures, measured via Vali’s even drops freezing method, of water droplets containing representative strains of three commonly recognized INA bacterial genera. These strains are Pseudomonas fluorescens, Erwinia uredovora, Xanthomonas campestris, Pseudomonas syringae pv. panici and Pseudomonas syringae pv. lachrymans. Results show that the first four bacteria strains do not have expected IN activity – freezing temperatures were 20.3±2.3°C, 21.8±2.3°C, 20.8±3.4°C, 19.9±3.3°C, respectively, when the concentration of the bacterial suspension was 10 8 cells/mL （OD 600 =0.25）. These are not significantly different from the freezing temperature of ultrapure water droplets, 20.8±2.7°C. However, a higher freezing temperature of 5.0±0.8°C was observed from measurement of P. syringae pv. lachrymans （ps1-10） contained in water droplets with the same bacterial suspension concentration. Additionally, average freezing temperatures of the water droplets are correlated with bacterial concentration. With a concentration lower than 10 5 cells/mL, droplet freezing temperature decreased significantly, and was even close to that of ultrapure water when the concentration was less than 10 4 cells/mL. This seems to indicate there was no IN activity for bacteria at such a low concentration. Based on the results, a question is raised that should be verified in the real atmosphere with lower bacterial concentrations. That is, can impacts of P. syringae on heterogeneous nucleation be attributed to their IN activity, or to some other unverified mechanisms？