Genetic diversity of Acidovorax oryzae in a single site in Mazandaran province, Iran.

Brown stripe, incited by Acidovorax oryzae is one of the most important and widespread diseases in rice (Oryza sativa) nurseries in Iran. Rice seedlings showing brown stripes were collected from suburb areas in southern Sari. Bacteria were isolated on plates of sorbitol neutral red agar. Species-specific PCR using trpB1/trpB2 and SEQID1/SEQID2 primer pairs resulted in amplification of the expected 478 bp and 514 bp long fragments, respectively. The 32 isolates subjected to REP-PCR analysis displayed 15 different banding profiles, with just one being shared by 10 isolates and 10 profiles were solitary and not shared by any isolates. Nonetheless, the isolates could not be different phenotypically. They appeared to be biochemically and nutritionally rather homogeneous while the genetic diversity as depicted in REP-PCR analysis was remarkable among the strains isolated from the closely located and even neighboring rice seedbeds. The implication of the findings in breeding programs is briefly discussed.

Phosphate solubilization potential and modeling of stress tolerance of rhizobacteria from rice paddy soil in northern Iran.

The purposes of this study were to evaluate the phosphate solubilization activity of bacteria isolated from the rhizosphere of rice paddy soil in northern Iran, and to study the effect of temperature, NaCl and pH on the growth of these isolates by modeling. Three of the most effective strains from a total of 300 isolates were identified and a phylogenetic analysis was carried out by 16S rDNA sequencing. The isolates were identified as Pantoea ananatis (M36), Rahnella aquatilis (M100) and Enterobacter sp. (M183). These isolates showed multiple plant growth-promoting attributes such as phosphate solubilization activity and indole-3-acetic acid (IAA) production. The M36, M100 and M183 isolates were able to solubilize 172, 263 and 254 µg ml(-1) of Ca3(PO4)2 after 5 days of growth at 28 °C and pH 7.5, and to produce 8.0, 2.0 and 3.0 µg ml(-1) of IAA when supplemented with L-tryptophan (1 mg ml(-1)) for 72 h, at 28 °C and pH 7.0, respectively. The solubilization of insoluble phosphate was associated with a drop in the pH of the culture medium and there was an inverse relationship between pH and solubilized P (r = -0.98, P < 0.0952). There were no significant differences among isolates in terms of acidity tolerance based on their confidence limits as assessed by segmented model analysis and all isolates were able to grow at pH 4.3-11 (with optimum at 7.0-7.5). Based on a sigmoidal trend of a three-parameter logistic model, the salt concentration required for 50 % inhibition was 8.15, 6.30 and 8.23 % NaCl for M36, M100 and M183 isolates, respectively. Moreover, the minimum and maximum growth temperatures estimated by the segmented model were 5.0 and 42.75 °C for M36, 12.76 and 40.32 °C for M100, and 10.63 and 43.66 °C for M183. The three selected isolates could be deployed as inoculants to promote plant growth in an agricultural environment.

Gibbsiella quercinecans as new pathogen involved in bacterial canker of Russian olive.

Russian olive (Elaeagnus angustifolia) is an economically important ornamental and crop plant. It has a wide range of biologically active compounds and is regarded as a unique medicinal plant with multiple applications. Members of the order Enterobacteriales isolated from trees are often associated with bacterial canker. During the growing season from 2017 to 2020, forty Gram-negative bacterial strains were isolated from Russian olive trees infected with cankers showing symptoms such as distinctive lesions on the trunk and branches, decline, weakness of trees, cracked bark, depressed brown to black lesions accompanied by exudation of gum, in the Kerman and Mazandaran Provinces of Iran. We used a polyphasic approach to identify and characterize these strains. Using a multilocus sequence analysis approach of four housekeeping loci, namely atpD, rpoB, gyrB, infB, and partial 16S rRNA gene sequences, isolates were identified as Gibbsiella quercinecans. These results were further supported by phenotypic and biochemical tests. Results of the biochemical, physiological and phenotypic experiments, indicated that the isolates are members of the Enterobacteriales and within the genus Gibbsiella. Pathogenicity of the G. quercinecans isolates was confirmed by fulfillment of Koch's postulates. To our knowledge, this is the first report of G. quercinecans as the causal agent of bacterial canker of Russian olive trees.

First report of a bifunctional chitinase/lysozyme produced by Bacillus pumilus SG2.

Bacillus pumilus SG2 isolated from high salinity ecosystem in Iran produces two chitinases (ChiS and ChiL) and secretes them into the medium. In this study, chiS and chiL genes were cloned in pQE-30 expression vector and were expressed in the cytoplasm of Escherichia coli strain M15. The recombinant proteins were purified using Ni-NTA column. The optimum pH and optimum temperature for enzyme activity of ChiS were pH 6, 50°C; those of ChiL were pH 6.5, 40°C. The purified chitinases showed antifungal activity against Fusarium graminearum, Rhizoctonia solani, Magnaporthe grisea, Sclerotinia sclerotiorum, Trichoderma reesei, Botrytis cinerea and Bipolaris sp. Moreover, purified ChiS was identified as chitinase/lysozyme, which are capable of degrading the chitin component of fungal cell walls and the peptidoglycan component of cell walls with many kinds of bacteria (Xanthomonas translucens pv. hordei, Xanthomonas axonopodis pv. citri, Bacillus licheniformis, E. coli C600, E. coli TOP10, Pseudomonas aeruginosa and Pseudomonas putida). Strong homology was found between the three-dimensional structures of ChiS and a chitinase/lysozyme from Bacillus circulans WL-12. This is the first report of a bifunctional chitinase/lysozyme from B. pumilus.