Earth’s radiation budget and frequency and intensity of precipitation are influenced by aerosols with ice nucleation activity (INA), i.e., particles that catalyze the formation of ice. Some bacteria, fungi, and pollen are among the most efficient ice nucleators but the molecular basis of INA is poorly understood in most of them. Lysinibacillus parviboronicapiens (Lp) was previously identified as the first Gram-positive bacterium with INA. INA of Lp is associated with a secreted, nanometer-sized, non-proteinaceous macromolecule or particle. Here a combination of comparative genomics, transcriptomics, and a mutant screen showed that INA in Lp depends on a type I iterative polyketide synthase and a non-ribosomal peptide synthetase (PKS-NRPS). Differential filtration in combination with gradient ultracentrifugation revealed that the product of the PKS-NRPS is associated with secreted particles of a density typical of extracellular vesicles and electron microscopy showed that these particles consist in “pearl chain”-like structures not resembling any other known bacterial structures. These findings expand our knowledge of biological INA, may be a model for INA in other organisms for which the molecular basis of INA is unknown, and present another step towards unraveling the role of microbes in atmospheric processes.

地球的辐射收支以及降水的频率和强度受到具有冰核活动（INA）的气溶胶（即催化冰形成的颗粒）的影响。一些细菌、真菌和花粉是最有效的冰成核剂之一，但在大多数情况下对 INA 的分子基础知之甚少。Lysinibacillus parviboronicapiens ( Lp ) 先前被鉴定为第一个具有 INA 的革兰氏阳性细菌。Lp的INA与分泌的纳米大小的非蛋白质大分子或颗粒有关。在这里，比较基因组学、转录组学和突变筛选的组合显示Lp中的 INA依赖于 I 型迭代聚酮合酶和非核糖体肽合成酶 (PKS-NRPS)。差速过滤与梯度超速离心相结合显示，PKS-NRPS 的产物与具有典型细胞外囊泡密度的分泌颗粒相关，电子显微镜显示这些颗粒由类似于任何其他已知细菌的“珍珠链”状结构组成结构。这些发现扩展了我们对生物 INA 的认识，可能是其他生物体中 INA 的模型，而 INA 的分子基础尚不清楚，并为揭示微生物在大气过程中的作用迈出了又一步。