فصلنامه زیست شناسی میکروارگانیسم ها
پیاپی 33 (بهار 1399)

The purpose of this study was to select moderate extremophile antagonistic Streptomyces strains from the Microbial Collection of Agricultural Biotechnology Research Institute of Iran to improve the growth and protection of cucumber against Phytophthora capsici, the causal agent of seedling damping-off disease in greenhouse conditions.

First, the antagonistic activity of eight strains of Streptomyces against three important cucumber pathogens including Pythium aphanidermatum, P. drechsleri and P. capsiciwas investigated in in vitro conditions. These strains were examined for physiological characteristics, plant growth promoting traits and siderophore and cellulase production in the presence of different amount of NaCl (0%, 6%, 10%, and 12%) and temperatures of 29, 37 and 42 °C. Three strains with a similar potential for auxin production including IT25 (salinity tolerant), IT20 (thermophilic) and SS14 with the highest growth inhibition percentage of P. capsici for further studies including SA production and the ability to induce plant growth and biocontrol of cucumber seedling under greenhouse conditions were selected.

The strains were able to produce siderophore at temperatures above 29 °C and siderophore production increased in SS14 and IT20 strains. Conversely, increasing the NaCl concentrations decreased siderophore production by Streptomyces. The increase in the cellulase activity at elevated temperatures was strain-dependent and was observed only for IT20. However, the increase in salinity did not change the activity of this enzyme. The treatment of soil with SS14 and IT20 increased shoot fresh and dry weights in all treatments. IT20 treatment reduced seedling damping-offby 83% compared to the infected control.

The two SS14 and IT20 strains, which had a good ability to control the disease and enhance plant growth, had common characteristics such as growth in the presence of 6% NaCl, siderophore production and cellulase activity under different temperatures and salinity conditions. The better performance of the IT20 and the poor performance of the IT25 may be related to their high temperature (42 °C) tolerance and intolerance, respectively, as well as their increased cellular activity and inactivity at this temperature.

Ciprofloxacin is a broad-spectrum antibiotic and a member of fluoroquinolones. Its main target in Escheichia coli is DNA gyrase. Ciprofloxacin induces the SOS response via RecA. The presence of RecF protein is essential for RecA activity. The recF is increased in the logarithmic phase by its operon promoter and the stagnation phase by its specific promoter. The activity of the specific promoter is dependent on rpoS. This study aimed to evaluate the expression of rpoS in a ciprofloxacin-resistant mutant.

To evaluate the expression of rpoS, cellular RNAs in the early and middle logarithmic phases of growth were extracted. Then, after synthetizing cDNA, the relative gene expression in the wild type and mutant strains was measured by real-time PCR.

Results showed that the extracted RNAs were free of contamination and have a suitable quality for the production of cDNA. Moreover, the expression of rpoS in the early and middle logarithmic phases after ciprofloxacin treatment in the high ciprofloxacin resistant mutant was approximately similar to the wild type strain.

In conclusion, it seems that the increased expression of recF was related to the operon promoter, and treatment with ciprofloxacin did not cause the stationary phase-like conditions.

The soil microbial community affects its fertility through the decomposition, mineralization, storage, and release of nutrients. Given the release of about 20-30% of photosynthetic materials in the rhizosphere, this environment has provided favorable conditions for the presence of microbial populations.

The aim of this study was to investigate the potential of rhizosphere and endophytic bacterial isolates isolated from the roots of wheat plant in terms of plant growth promoting (PGP) traits to identify their 16S rRNA sequences. To this end, the isolated bacteria were first screened for the production of indole-3-acetic acid (IAA) in the presence of tryptophan in the culture medium, and then they were tested for their ability to dissolve inorganic and organic phosphates. In the next step, other growth promoting factors including siderophore production and ACC-deaminase were investigated.

Among the isolates obtained from rhizosphere and intra-root of wheats, 15 rhizosphere and 7 endophyte isolates were selected based on their ability to induce growth promoting properties. A total of 7 isolates belonged to the Bacillus, 4 isolates to Pseudomonas, 2 isolates to Staphylococcus, 2 isolates to Paenibacillus, and the rest belonged to the genera Sphingobacterium, Lysinibacillus, Advenella, Enterobacter, Variovorax, and Plantibacter.

According to the obtained results, the dominant genera among the rhizosphere and endophyte isolates were Pseudomonas and Bacillus. Increased yield through increased nutrient bioavailability is the result of siderophore production, dissolution of insoluble inorganic and mineral phosphates, the production of growth factors and plant growth hormones, especially indole acetic acid, which can increase crop growth indices and yield. It also has to protect the environment and the plant.

Among the mycorrhizal fungi, arbuscular mycorrhizal fungi are the most common symbiotic species with plants. Root colonization by these fungi increases plant resistance to biotic and abiotic stresses, enhances growth through increasing elements uptake, improves the water connection of plants, and protects plants against diseases.

In this study, eight plants were selected from Joupar and Mahan regions of Kerman province and were sampled from 0 to 30 cm depth of rhizosphere of each plant, which included thin soils and roots, to calculate the frequency of arbuscular mycorrhizal fungi in the soil, identify spores, and determine the percentage of root colonization. For staining the roots, Philips and Hayman’s method was used and root colonization percentage was determined. Spore density in soil samples was obtained after the extraction of spores from 10 grams of the soil sample by the wet sieve method and existing spores and also dominant spores in the soil of each plant were determined and then the data were statistically analyzed.

All the examined root samples showed a symbiotic relationship with arbuscular mycorrhizal fungi. The percentage of colonization in evergreen, oregano, chicory, safflower and castor plants was 100% and in purslane, gall and chamomile were 98%, 95%, and 88%, respectively. The average number of spores per 10 grams soil was 18, 62, 16, 34, 3, 15, 25, and 7 respectively. Based on statistical analysis, it was found that there is a direct relationship between the number of spores and the percentage of mycorrhizal colonization in most plants. Then, the available spores as well as the dominant spores in the soil of each plant were identified.

High spores per 10 grams of soil and the high percentage of mycorrhizal colonization in the study area indicated that such climates are the valuable natural repository for plant species, animals, and microorganisms.

Folic acid or vitamin B9 is one of the most essential vitamins, which plays a key role in the transport of carbon and many biochemical pathways and its deficiency can lead to neurological diseases, anemia and developmental problems in children. The present study aimed to take a step towards producing this vitamin from native strains by isolating and sequencing the folic acid production gene from soil isolated bacillus and cloning it in Escherichia coli.

In this study, 40 samples were collected from 5-10 cm depth from different areas around Sirjan city. Bacillus bacteria were isolated by molecular and biochemical methods. By PCR method, bacteria with FOLA gene were identified and the amplified gene was cloned into E. coli and sequenced. Gene expression was then evaluated by Real time PCR and its phylogenetic relationships were determined.

As a result of screening of 40 soil samples sent to the laboratory, a total of 12 suspected colonies were isolated from Gram-positive bacilli which were identified based on morphological, microscopic and biochemical characteristics and all species were identified as having FOLA gene. FOLA cloning was performed successfully and confirmed its gene expression.

In the present study, the FOLA gene from Bacillus Halotolerance isolated from the soils of the surrounding areas of Sirjan was successfully cloned into PTG19-T expression vector and its successful expression showed that it could be expanded by this method for industrial production of Folate.

Nattokinase is an enzyme extracted from Japanese food produced in the fermentation process. This enzyme has significant positive effects in the treatment of cardiovascular diseases, the treatment or prevention of amyloid diseases such as Alzheimer disease and the reduction of blood cholesterol. This genomic study aimed to investigate the Nattokinase isolated from soil bacilli in areas around Tehran and its cloning in Escherichia coli bacteria for medicinal use.

In this study, 60 samples were collected from 5-10 cm depth of soil of different areas around Tehran and their Bacillus bacteria were isolated by molecular and biochemical methods. By the PCR method, the bacteria with the Nattokinase gene were identified and the amplified gene was cloned into E. coli and sequenced. The gene expression was then evaluated by Real Time PCR and its phylogenetic relationships were determined.

As a result of screening soil samples sent to the laboratory, a total of 12 suspected colonies were isolated from Gram-positive bacilli which were identified based on morphological, microscopic, and biochemical tests. Then, 11 species was determined as target genes. The cloning and expression of Nattokinase gene were successfully performed and the homology of 99-100% with other enzymes was observed.

In the present study, the Nattokinase gene from Bacillus subtilis RH5 isolated from soils around Tehran was successfully cloned into PTG19-T expression vector. The successful expression of its gene showed that it could be expanded by this method for industrial production.