اولین گزارش از باکتری‌های گرم مثبت دارای فعالیت هسته یخ جدا شده از درختان میوه هسته‌دار در ایران

Freezing causes considerable economic losses to many agricultural crops, especially stone fruit trees. Ice-nucleating bacteria can induce ice formation at temperatures above -10°C and are commonly found on nearly all plants in nature. Some of the most known species are: Pseudomonas syringae, Pseudomonas fluorescens, Pseudomonas viridiflava, Erwinia herbicola, Erwinia ananas and Xanthomonas campestris which have an important role in ice formation in plants. Ice particles may be formed by different processes, which heterogeneous ice-nucleation is produced by the presence of external agents such as microorganisms. Ice-nucleating bacteria are often Gram-negative, epiphytic and pathogenic bacteria. The aim of this study was isolation and identification of epiphytic ice-nucleating bacteria on the surface of stone fruit trees (apricot, peach, sour cherry, cherry and plum) from areas of Zanjan, Maragheh and Azarshahr. A total of 77 bacterial strains were isolated on nutrient agar medium. Approximately 18/18% strains had positive ice nucleation activity at -7°C for time period 5-8 min as compared with the control (Pseudomonas syringae pv. Syringae). Identification of Gram-positive strains based on physiological and biochemical tests, including gram reaction, oxidase, production and non-production fluorescent on Kingʼs B medium, aerobic and anaerobic growth, hypersensitive reaction on tobacco plants, production of soft rot on potato slices, gelatin, tween 80 and starch hydrolysis, lecithinase activity, nitrate reduction, grow at 4, 37 and 40°C. Also, molecular identification was conducted by amplifying the 16SrRNA gene using the pA/pH universal primer pair and partial sequencing of this gene. Blast search and phylogenetic analysis showed that Gram-positive strains 5Dc, 4Vd and 6Za respectively had 99% similarity with Bacillus pumilus MG721541, Microbacterium foliorum MH368761 and Staphylococcus sciuri MH370473 available in GeneBank.To the best of our knowledge, this is the first report of the ice-nucleating activity of these Gram-positive bacteria.