فصلنامه زیست شناسی میکروارگانیسم ها
پیاپی 45 (بهار 1402)

Seemingly worthless agricultural residues (wheat straw, olive pomace) and industrial (wood chips, sugarcane bagasse) constitute a large amount of waste that leads to environmental pollution and health hazards. Fungi, as consumers of organic matter wastes, establish a material recycling cycle and also eliminate the problems related to air pollution caused by the incineration of wastes.

The present study was conducted with a completely randomized design with three replicates in Sistan Damfarm in 2019. Experimental treatments include substrates of wood chips, wheat straw, sugarcane bagasse, sugarcane bagasse+wheat bran (90 to 10), sugarcane bagasse+olive pomace (90 to 10), wood chips+wheat bran (90 to 10), wood chips+olive pomace (90 to 10), wheat straw+olive pomace (90 to 10), wheat straw+wheat bran (90 to 10). Spawn of H. ulmarius and A. aegerita fungi were prepared and the substrates were inoculated with spawn.

In the fungus H. ulmarius, the highest yield (467.54 g), dry matter (50.24 g), the highest amount of total polysaccharide (12.29 mg/g dry matter) and the shortest time (14 days) required to complete the spawn run. The lowest time for precocity (26 days) was allocated to the combined substrates of wheat straw with wheat bran (90 to 10). In the fungus A. aegerita, the highest yield (72.81 g), dry matter (9.22 g), the highest amount of total polysaccharide (11.33 mg/g dry matter) and the shortest time (15 days) required to complete the spawn run. The lowest time for precocity (29 days) was allocated to the combined substrates of wood chip with wheat bran (90 to 10).

A wheat straw substrate for H. ulmarius and wood chip substrate for A. aegerita were introduced as the best substrates.

Indole acetic acid (auxin) is a plant hormone that, in addition to plants, is produced by a number of bacteria. The aim of the present study was to optimize the production of indole acetic acid from whey substrate by bacteria isolated from rhizosphere and phyllosphere of plants.

The desired bacteria were isolated and purified from phyllosphere and rhizosphere of green beans, cowpea, mint, and parsley plants. The ability of isolates to grow in whey substrate and production of auxin was evaluated. The effect of pH and temperature parameters on the function of isolates was investigated. Impure auxin powder was prepared from the bacterial culture in whey substrate and its function was evaluated on the seed growth rate of lentil and mung bean plants.

Out of 26 isolated bacterial samples, 5 isolates (19.2%) had the ability to produce indole acetic acid and grow in whey substrate simultaneously. Two isolates with the highest auxin production capacity were identified using 16S rDNA region sequencing. One isolate had 97% similarity to Enterobacter soli and the other isolate had 99% similarity to Enterobacter mori. These isolates showed the highest auxin production capacity at 30 and 35°C respectively and in pH 7. Seed irrigation of the studied plants with produced auxin solutions significantly increased the longitudinal growth of stems of these plants in comparison with control solutions.

Auxin-producing strains can be isolated from soil and plants, and by using inexpensive substrates such as whey, this phytohormone can be produced on an industrial scale and used as a plant growth stimulant.

Staphylococcus aureus is one of the pathogenic bacteria in humans that causes a wide range of diseases. Biofilm formation protects S. aureus against adverse environmental conditions and the host immune system. The genes that encode the most important biofilm constituents belong to the ica operon, one of the most important of which is the icaA gene. Rifampin is a broad-spectrum antibiotic, and garlic has beneficial antimicrobial effects due to its active ingredient allicin. In the present study, the antimicrobial effect of garlic extract at the phenotypic and molecular level and its effect on icaA biofilm gene expression and its comparison with rifampin were investigated.

A standard and two pathogenic strains of Staphylococcus aureus were evaluated. Antibiogram tests, minimum inhibitory concentration, and minimum bactericidal concentration were performed with rifampin antibiotic and garlic extract. A biofilm phenotypic test was performed with a 96-well microplate. After RNA extraction from the samples treated with rifampin and garlic extract, cDNA synthesis and then Real-time PCR were performed and the expression of icaA gene was measured.

The antibiogram test showed the antimicrobial effect of garlic extract on at least the standard strain and one of the pathogenic strains as compared to rifampin. The results of Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) were determined for all three strains for rifampin and the combined combination of rifampin and garcin were 375 and 750 μg / ml, respectively. Real-time PCR results showed that in all studied strains, garlic extract and rifampin were able to reduce the expression of icaA gene and the combined use of these two substances led to a significant reduction in the expression of this gene. For the standard strain, rifampin and garlic extract reduced icaA expression to 88% and 60% in the control sample, respectively, and the combination of these two substances resulted in a reduction of icaA biofilm gene expression by about 50%.

In general, it can be concluded that rifampin antibiotic can be effective in inhibiting pathogenic bacteria such as Staphylococcus aureus. Garlic extract can also be used as an anti-bacterial drug at both phenotypic and molecular levels.

Manganese oxide nanoparticles are used as strategic materials in various industries such as battery manufacturing, water and wastewater treatment, pharmaceutical industries, etc. because of economic reasons and have special physical and chemical properties. The production of manganese oxide nanoparticles is one of the secondary metabolites in bacteria. Considering that the manganese and narcissus mine in Qom province is one of the most important sources of manganese for manganese-oxidizing microorganisms, this project was done for the first time on mine soli.

In this study, 100 soil samples were collected from different areas of the manganese mine and inoculated in the selective enrichment medium K and heated on a rotary shaker. The strains obtained from the culture in a manganese-containing medium were evaluated by the benzidine test to evaluate the oxidation ability of manganese and properties of manganese oxide nanoparticles including morphology, size, and chemical structure using confirmation techniques such as UV-VIS, FTIR, XRD, FESEM, TEM. Using the FESEM histogram, the size of nanoparticles in the range of 10 nm was determined and the selected strain was molecularly identified.

For the first time, native actinobacteria strain with the ability to oxidize manganese and nanoparticle production extracellularly was isolated from the Venarj manganese mine soil of Qom and was biochemically and molecularly identified. The strain was registered in the NCBI with the name Streptomyces xantholiticus HA98 and identification code OM669940.

Based on the importance of manganese oxide nanoparticles in medical, industrial, and pharmaceutical industries and that the Venarj manganese mine soil of Qom is an important source for manganese-oxidizing microorganisms, the present study was conducted for the first time in Iran on this mine soil so that the microorganism with the above properties could be identified and used in various industries

Lactoferricin, a cationic peptide, contains 25 amino acids and is located in domain I of the N-lactoferrin lobe. This peptide has more antibacterial activity than lactoferrin. The aim of the present study was to investigate the effects of Lactoferricin on the growth of Staphylococcus aureus and Pseudomonas aeruginosa.

After isolation from camel milk, lactoferrin was purified using CM-Sephadex C-50 ion-exchange chromatography. Then, Lactoferricin was prepared by modified Law and Reiter methods and the protein was analyzed by polyacrylamide gel electrophoresis and the antibacterial effect of different concentrations of lactoferricin against Pseudomonas aeruginosa and Staphylococcus aureus was investigated.

According to the obtained results, a concentration of 5 µg/ml Lactoferricin had the least inhibitory effect on the studied bacteria. Also, concentrations of 15 and 23 µg/ml Lactoferricin with the inhibitory potency of 26-48 and 42-50% had the greatest inhibitory effect on Staphylococcus aureus and Pseudomonas aeruginosa, respectively.

Based on the results of the study, Lactoferricin has a significant and dose-dependent inhibitory effect on the growth of Staphylococcus aureus and Pseudomonas aeruginosa. The results show that Lactoferricin as an antibacterial agent can be useful in a variety of commercial programs to control the growth and survival of many pathogens.

Among metal nanoparticles, elemental selenium nanoparticles (SeNPs) are considered for their low toxicity and vitality in the human body. Yarrowia lipolytica yeast, due to its reductase enzymes, has the ability to accumulate and detoxify heavy metals and reduce metal salts to nanoparticles with a narrow size and less dispersion. The aim of the present study was to use Y. lipolytica strain MP10 as a biological safe source for the biological synthesis of SeNP.

Agar dilution method was used for determining the resistance pattern of Y. lipolytica strain MP10 to selenite oxyanion. Synthesis of SeNPs was investigated under resting cell strategy. The effects of selenite oxyanion concentrations and also time incubation on the production rate, size, and dispersity of SeNPs were investigated in the bioconversion reaction. SeNPs produced with Y. lipolytica strain MP10 were defined by images obtained from Scanning Electron Microscopy (SEM) analysis, energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR).

The obtained results demonstrated that Y. lipolytica strain MP10 showed tolerance to selenite oxyanion up to 10 mm. The yeast strain, at the optimal condition of 4 mM sodium selenite, and after 24 hours of incubation, was able to produce spherical SeNPs with an average size of 70 nm. As the incubation time increased, the dispersion of spherical SeNPs reduced and the average size of the nanoparticles increased to 117 nm after 72 h incubation. 

Discussion and Conclusion:

The present study is a report on the capability of native yeast Yarrowia lipolytica for the successful synthesis of SeNP under resting cell strategy and the improvement in the dispersion and particle size of the nanoparticles in the optimal incubation time.

Due to the increasing concern about the growing resistance of pathogenic bacteria to a variety of common antibiotics, it is vital to find and introduce new drugs to treat bacterial infections. To this end, intensive efforts need to be taken to find novel antimicrobial agents with diverse antimicrobial modes of action, preventing pathogen growth. Combination therapy using current antibiotics and other biological or chemical molecules might be efficient as an exciting new approach.

In the present study, the synergistic antibacterial activity of Dermastin B1 recombinant peptides isolated from transgenic T1 tobacco plants either alone or in combination with peppermint essential oils were evaluated against Xanthomonas translucen, Xanthomonas perforans, Xanthomonas citri, Xanthomonas gardneri and Pseudomonas syringae by measuring the Fractional Inhibitory Concentration (FIC) index at different concentrations.

The results of this study showed that the MIC of Dermaseptin B1 peptides and the peppermint essential oils against bacteria were 50 µg/ml and 4.6 µg/ml, respectively. FIC index showed a synergistic effect of peppermint essential oils with Dermaseptin B1 recombinant peptide with FIC=0.49.

The results of this study suggest that Dermasptin B1 recombinant peptides can be effective either alone or in combination with the peppermint essential oils to control bacterial infections. However, it seems that there is a synergistic effect between recombinant peptides and peppermint essential oils in combat against phytopathogens.