فصلنامه دنیای میکروب ها
سال دوازدهم شماره 3 (پیاپی 40، پاییز 1398)

In the past, the classification of cyanobacteria was only based on the morphological characteristics; however other markers such as accurate molecular methods have been recently used. This study aimed to identify several heterocystous cyanobacteria by polyphasic taxonomy and to investigate the multigenic approach in enhancing the accuracy of  cyanobacterial identification.

After analyzing the morphological features and initial identification, the 16SrRNA gene along with tufA, rbcL, psbA, and rpoC1 functional genes were used to evaluate the taxonomic status and phylogenetic relationships. For this purpose, after DNA extraction, amplification and sequencing of gene fragments, the exact position of the strains was determined by making phylogenetic trees, based on the corresponding genes using MEGA software.

Among  the functional genes studied, the rpoC1 gene was able to discriminate genera very well, a result that completely confirmed 16SrRNA phylogenetic results. Finally based on the results, 4 samples from the Desmonostoc genus and 2 samples from the Calothrix genus were introduced. 

The results of this study demonstrate the ability of the rpoC1 gene to discriminate genera correctly and confirm the morphological and phylogenetic results of 16SrRNA gene analysis. A phylogenetic study using the rpoC1 gene marker helps to clarify phylogenetic relationships among cyanobacteria. Moreover, it provides further evidence of their chloroplast origin and the presence of different evolutionary pathways among them.

Brucellosis has always been a threat to the health and economy of the community. The limitations of human and animal disease detection methods justify the need for new diagnostic methods. This study was aimed to compare the sensitivity of colorimetric strategy based- immunosensors in the diagnosis of Brucella abortus with those of culturing and PCR methods.

The colored silica nanoparticles and paramagnetic nanoparticles after synthesis were conjugated with polyclonal antibody to form EDC/NHS complexes to form probe sequences, respectively. These probes were collected after being added to serial dilutions of B. abortus and completing the reaction. Then, with releasing organic dye from the silica structure, absorbance intensity was measured at 670 nm. On the other hand, at the time of each dilution, the corresponding chromosomal DNA was extracted by a DNA extraction kit and used for PCR analysis. The results of all three tests were ultimately compared.

Based on the results, the detection range of the immunosensor and culture was the same and equal to 1.5×103 - 1.5×108 CFU mL-1. But, the limit of detection for immunosensor and culture was measured as 450 CFU mL-1 and 400 CFU mL-1, respectively. The results of the PCR test exhibited a wide dynamic range of 1.5×104 to1.5×108 CFU mL-1, with LOD of 5000 CFU mL-1.

Comparing the results of this study showed that the proposed immunosensor is capable of replacing conventional B. abortus detection methods and can be considered as an on-site diagnostic tool, with high sensitivity.

Antioxidants reduce the risk of cardiovascular diseases, and stroke and prevent the development of cancer by neutralizing free radicals. The present study aimed to produce and optimize the production of antioxidant compounds by Aspergillus strains.

Fungi samples were collected from different regions of Isfahan province or obtained from the Persian Type Culture Collection. Purified fungi samples were inoculated to the Czapek medium to produce antioxidant compounds. Screening and comparison of antioxidant properties of the selected strains were carried out using four assays including free DPPH (Diphenyl pycryle-Hydrazyl) radical reduction, iron radical recovery, and total phenol content and flavonoid content assays. Fungi antioxidant activity was optimized in terms of pH, temperature, and type of carbon and nitrogen sources by single factor and detailed factorial (Taguchi) designed experiments.

The highest antioxidant activity was observed in Aspergillus niger isolated from the soil of the Iron melting factory and the highest amount of flavonoid content was shown by Aspergillus fumigatus isolated from greenhouse soil. DPPH radical reduction rate by Aspergillus niger was 89.9% in the optimum condition (pH 6, the temperature of 25°C, sucrose as carbon source and potassium nitrate as nitrogen source). Optimization by Taguchi designed experiments resulted in a 10-15 percent increase in antioxidant compounds production.

Autochthonous isolated fungi had high potential to produce antioxidant compounds and can be proposed to related industries.

Selenium nanoparticles have a wide range application in industry, biomedical and environmental fields due to their unique physical, chemical and photoelectrical properties. This study was aimed to use aquatic bacteria in bioreduction of selenite oxyanioninto elemental nano-selenium.

Synthesized selenium nanoparticles were characterized by spectroscopic analysis and electromicrographs prepared by scanning electron microscopy (SEM). The efficacy of the antimicrobial activity of the synthesized selenium nanoparticles against some Gram-positive and Gram-negative human pathogenic bacteria was also investigated by the agar well diffusion test.

Sixteen selenite-resistant bacterial strains were isolated based on selective enrichment techniques in Tryptic Soy Agar (TSA) medium containing 5 mM selenite ion. Our results showed that Pseudomonas alcaligenes SR5 coastal seawater isolate can reduce selenite oxyanion into selenium nanoparticles. Furthermore, the results showed that extracellular selenium nanoparticles with an average size of 36 nm were formed in an optimum selenite concentration of 3 mM and an optimum initial biomass concentration of 15 g/l, following 96 h incubation at 25ᵒ C at (200 rpm under resting cell condition.

The current study is the first report on extracellular synthesis of selenium nanoparticles using P. alcaligenes. The produced bio-nanoparticles showed a growth inhibitory effect against four tested pathogenic bacterial strains.

Lipases are important hydrolytic enzymes produced by various microorganisms such as bacteria. This enzyme is applied in various industries including food and pharmaceutical industries. This study aimed to isolate and identify lipase-producing bacteria from various sources to use in different industries.

Sampling and screening of lipase- producing bacteria were carried out from wastewater and soils of Habib-abad refinery, wastewater and slugs of Golbahar oil factory, sheep’s tail fat, and sesame meal. To evaluate the enzymatic activity, bacterial isolates were cultured in lipid-based media, where the supernatant was used for the next assay. A quantitative assessment of enzymatic activity was performed using a spectrophotometer, in the presence of para-nitrophenol acetate at the temperature of 28°C. The identification of bacterial isolates was carried out by macroscopic, microscopic and molecular analysis.

Screening bacterial isolates and the results of enzymatic activity assays showed strain 31 as the superior one. Molecular analysis results identified this strain as Bacillus thuringiensis L26. The highest enzymatic activity and stability were obtained at the temperature of 48°C, pH value of 8.5, and in the presence of sodium chloride, calcium chloride, potassium chloride, magnesium chloride, zinc sulfate, and manganese chloride, respectively.

Our results showed the stability of tested lipase enzymes under alkaline conditions and the presence of different cations. Therefore, further complementary tests are recommended o assess practical uses.

Rice bacterial blight is one of the major factors limiting global rice production. Though the most effective method for controlling this disease is using resistant varieties, they are not stable in farm conditions due to high variability and rapid evolution of pathogenic races. This study was aimed to evaluate rice endophyte bacteria's ability to improving plant growth and biologically controlling Xanthomonas oryzae pv. oryzae.

At the first screening of endophyte isolates was performed to evaluate antagonistic activity against Xanthomonas in tryptic soy agar medium. The stimulation of plant growth by bacterial endophytes was assessed under the growth chamber and greenhouse conditions. The effect of bacterial isolates on disease severity and some rice growth factors under greenhouse conditions were determined, as well. In the final stage, the expression of the Phenylalanine ammonia-lyase gene by endophytic isolate Bacillus subtilis was evaluated using real-time PCR.

In terms of rice seed seedling vigor index, OS40, OS23, OS43, and OS31 isolates had a significant statistical effect as compared to control. Moreover, the use of OS3, OS23, OS31, and OS40 endophytes increased plant growth parameters. OS40 and OS23 bacterial inoculants were more successful in reducing the severity of the disease and the promotion of plant growth. PAL expression level during the experiment period was significantly higher and faster in plants treated with OS40than those treated only with Xanthomonas- isolates.

Rice bacterial endophytes could increase plant growth and reduce disease severity, thus they can be considered as a promising and environmentally- a friendly strategy for sustainable agriculture development.

Staphylococcus aureus is one of the important nosocomial infection agents. Recently, S. aureus strains have become resistant to ciprofloxacin and the efflux pump is considered as its contributor. Herein, we investigated the presence, expression, and activity of efflux pump genes (norA and norB) among ciprofloxacin-resistant S. aureus isolates.

A total of 250 clinical samples were subjected to isolation of S. aureus strains. The antibiotic resistance pattern was characterized and the presence and expression level of norA and norB genes was assessed using PCR test and real-time PCR test, respectively. Finally, active efflux pumps were detected in ciprofloxacin-resistant S. aureus strains using the ethidium bromide test.

Among total clinical samples, 50 S. aureus strains were recovered. Of this 12 samples (24%) were resistant to ciprofloxacin. Moreover, norA and norB genes were found in 100 % and 83% of ciprofloxacin-resistant isolates, respectively. All ciprofloxacin-resistant isolates exhibited active efflux pumps. Real-time PCR results revealed that the isolates are more resistant to ciprofloxacin having a high level of efflux pump gene expression.

The results of this study showed that norA and norB efflux pump genes play an important role in resistance to ciprofloxacin in S. aureus strains.

Grapes infected with Aspergillus can produce ochratoxin A (OTA) in the processing of beverages such as wine or grape juice. This study aimed to evaluate the antifungal biological potential of two low-fermenting native yeast isolates (A01 G01) and three standards (Saccharomyces cerevisiae, Candida guilliermondii, Metschnikowia agaves) yeast isolates against Aspergillus niger and their ability to remove OTA in grape juice and its products, without any considerable alcohol production during the process.

Two native yeast isolates (A01 and G01) were obtained from Malayer apples and grapes, respectively, and inoculated on the PDA culture medium. Native isolates were identified by sequencing D1 and D2 and ITS 1 and ITS2 regions of the ribosomal DNA gene.

The results of DNA sequencing identified both native isolates as Saccharomyces. All strains showed a significant ability in inhibition of A. niger growth both on grape berries and in culture media. Meanwhile, yeast isolates produced a trace amount of alcohol.

Biological control of A. niger and OTA-decontamination using yeast is proposed as an approach to meet the Islamic dietary laws regarding the absence of alcohol in halal beverages.