فصلنامه زیست شناسی میکروارگانیسم ها
پیاپی 49 (بهار 1403)

The purpose of the present study was to investigate the antibiotic resistance of culturable bacteria following the increase of three commonly used antibiotics in three agricultural, rangeland, and mine soils with different amounts of heavy metals. Antibiotics amoxicillin, cefixime, and metronidazole were used in amounts of 100 and 200 mg per kilogram of agricultural, rangeland, and mine soils. Then, in a short time incubation (zero, 1, 3, and 7 days), the abundance of bacteria in nutrient agar medium and the percentage of resistant bacteria in nutrient agar medium with antibiotics (16 µg of amoxicillin, 2 µg of cefixime, 8 µg of gentamicin, 16 µg of metronidazole and 8 µg of tetracycline per milliliter of nutrient agar) were counted and estimated. The percentage of bacteria resistant to cefixime, gentamicin, and tetracycline in mine soil, especially rangeland soil, which had high contamination with heavy metals, was higher than in agricultural soil, and only the percentage of bacteria resistant to amoxicillin and metronidazole was higher in agricultural soil than mine soil. In rangeland soil, 100% of bacteria were resistant to the tested antibiotics except for tetracycline. Treatment of soils with amoxicillin caused an increase in the number of resistant bacteria, which was especially evident in agricultural soils at a concentration of 200 mg.kg-1. The same finding was also seen in the application of cefixime, but in mine soil, the high concentration of this antibiotic showed a decrease, and the percentage of resistant bacteria in both rangeland and agricultural soils was close to 100%, but in mine soil, it reached less than 20%. There was a significant increase in the number of resistant bacteria in the soils treated with metronidazole compared to control soils. But, in this treatment, the response of agricultural soil bacteria to a concentration of 200 mg.kg-1 was decreased, and mine soil did not show such a response. In all treatments, the bactericidal power of tetracycline and then gentamicin in the concentrations used in the culture medium was higher compared to the three antibiotics of amoxicillin, cefixime, and metronidazole. Antibiotic resistance of soil bacteria is dependent on soil contamination with heavy metals and diversity of soil bacteria, genetic pool, and ability to move resistance genes between them. The increase of antibiotics in the soil, depending on the characteristics of the soil and the antibiotic causes the dominance of special and resistant species, which increases the transfer of resistance genes and their abundance in the environment.

In recent years, the need for L-asparaginase in different industries has increased. L-asparaginase obtained from microorganisms is cost-effective, has no harmful effects on the environment, and improves the quality of products. In the present study, L-asparaginase-producing microorganisms were isolated and optimized from different sources, and selected strain enzymes were produced. L-asparaginase-producing yeasts were randomly isolated and purified from different parts of Isfahan. Strains were screened for L-asparaginase production. Then, the superior yeast strain with the highest enzymatic activity was selected for optimization. Under suitable pH, temperature, time, carbon source, and nitrogen source, multi-factor optimization was performed using response-level statistical software to investigate the simultaneous effect of several factors on production and the highest enzyme activity. In the present study, 5S2 yeast isolate led to the formation of the highest halo of L-asparaginase. This strain was first introduced as the L-asparaginase-producing strain and was registered in the NCBI database under Diutina mesorugosa strain SBG-IAUF-2 with access number MZ901211. Yeast 5S2 with enzyme activity equivalent to 1722.8 u / ml was selected as the selected strain for optimization. The results of multivariate optimization of enzyme activity showed that at pH 7, a concentration of 2% glucose as carbon source, the attention of 10% L-asparagine, a temperature of 35°C, and a time of 120 hours, there is the highest enzyme production activity and curve RSM is located in the optimization area. In the present study, after recording 5S2 yeast isolate for the first time as an L-asparaginase-producing strain in the NCBI database, extracellular L-asparaginase produced by the 5S2 yeast strain was introduced due to its high enzymatic activity as a potent strain in the production of L-asparaginase enzyme.

One of the concerns of today's world is environmental pollution caused by heavy metals, and in this regard, the element selenium is very important due to its low amount in the environment. Bioremoval of metals is one of the cleanest and cheapest methods of biological absorption. The purpose of this research is to isolate and evaluate selenium-resistant strains for the bioremoval of this metal from aquatic environments.

By isolating selenium-resistant strains, the bioabsorption rate of the selected types was investigated in different conditions of acidity, temperature, and biomass amount at different times. In between, two isolates were resistant to the concentration of 400 mM sodium selenite, which were identified after performing biochemical and genetic tests.

The highest absorption rate in terms of inoculated biomass was related to Thalassospira permensis and Bacillus thuringiensis at 4% in 20 and 60 minutes, respectively. The highest amount of absorption was obtained by Bacillus at an acidity of 5 during 40 minutes and by Thalassospira at an acidity of 7 and a time of 60 minutes. The optimal temperature for the two strains was 25 °C and it was found that Thalassospira permensis had the best effect in 20 minutes and Bacillus thuringiensis had the best effect in 40 minutes. In addition, Thalassospira permensis was the best choice for selenium bioabsorption by absorbing 95.1% of total selenium with 4% of the biological mass in a period of 20 minutes, at acidity equal to 6 and 25 °C.

Thalassospira permensis absorbed 95.1 mgL-1 of 100 mgL-1 of sodium selenite in the culture medium within 20 minutes by biomass 4%. Thus, it had a high bioabsorption rate and became a suitable candidate for further studies to remove selenium from the relevant wastewater.

This study aimed to evaluate the prevalence of Campylobacter isolates based on the presence of certain invasive genes. The experimental study tested 392 samples from Behbahan city. After culturing the samples, microbial identification was performed using Gram staining. Molecular identification of Campylobacter isolates was then conducted using PCR and suitable primers for invasive genes cdtA, B, C, cadF, pldA, ciaB, and 16S rRNA. According to the Gram staining results, 50 samples were infected with Campylobacter. Of these, 37 (74%) were chicken samples, 8 (16%) were cow samples, 2 (4%) were sheep and goat samples, and 3 (6%) were water samples. Analysis of the 16S rRNA gene sequence showed that 72% of the contamination was related to Campylobacter jejuni and 28% was related to Campylobacter coli. Overall, the prevalence of Campylobacter jejuni in isolated samples was significantly higher than that of general Campylobacter (p=0.012). Among the Campylobacter jejuni isolates, the highest prevalence was related to the CdtC toxin production gene (76.2%), and among the Campylobacter coli isolates, it was related to the CdtB toxin production gene (30.2%). Although chickens are considered the main sources of Campylobacter species, it is necessary to investigate the significance of other contamination sources, especially cattle and sheep, to assess their role in human infections. Therefore, necessary precautions must be taken for human consumption, and hygiene standards must be maintained in storage areas, along the slaughter line, and in stores.

Herein we evaluate the effect of secondary metabolites from the cyanobacteria Anabaena sp. on the expression of vancomycin resistance genes in Staphylococcus Saprophyticus.. This study is motivated by the growing concerns of multi-drug resistant S. saprophyticus strains and the need for alternative antimicrobial agents. of During a two-month period, 120 clinical samples were collected from elderly patients referred to Tehran hospitals. S. saprophyticus isolates were identified using both phenotypic and chemical tests. Subsequently, molecular methods were employed to detect the presence of van genes. The microbroth dilution method used to determine the sensitivity of the bacterial isolates to the methanolic extract of Anabaena sp. . Finally, real-time PCR was employed to measure the expression level of van genes compared to the 16S rRNA gene in S. saprophytic isolates treated with the cyanobacterial secondary metabolite. Among the 83 bacterial isolates obtained from the clinical samples, only eight were identified as S. saprophyticus. One isolate harbored the vanA gene, while two isolates possessed the vanB gene. The minimum inhibitory concentration (MIC) of the cyanobacterial secondary metabolite against S. saprophyticus was 750 μg/mL, with a sub-MIC of 325 μg/mL.  Importantly, the expression level of vanA and vanB genes in the strains treated with the cyanobacterial secondary metabolite down-regulated compared to the reference gene (16S rRNA). The findings suggest that the secondary metabolites from Anabaena sp. possess a potent antimicrobial effect and can potentially reduce the expression of antibiotic resistance genes in S. saprophyticus. This paves the way for the development of a new generation of anti-staphylococcal drugs.

The stability of enzymes to heat and pH is one of the most important determining factors in their application. In this research, achieving thermostable and pH-stable cellulase was aimed by screening in one of the Hot springs of Garab in northeast Iran. The samples collected from one of the Hot springs of Garab, in Razavi Khorasan province in Iran, were used to isolate, screen, and identify bacteria capable of producing thermostable cellulase. The cultures were cultured at 45°C and under aerobic conditions. The bacteria were isolated on a CMC agar medium. Initial screening of the isolates was done based on specific culture medium, salt tolerance, and temperature changes. Then, their additional screening was done by evaluating endoglucanase activity at different temperatures and pH using qualitative and quantitative methods. Finally, the molecular identification of the selected isolate was done by 16S rRNA gene sequencing. The results of this study, led to the introduction of a selected strain identified primarily as Bacillus sp. G362, a moderate halophile growing in 6%(w/v) salt concentration.  It showed high endoglucanase stability at 55°C and high stability in a wide range of acidic and alkaline pH. The studied Hot spring, like some other Iranian Hot springs, has cellulase-producing bacteria, which Bacillus sp. G362 is capable of producing endoglucanase showing the thermostablity and pH stability at a wide range of alkaline and Acidic pH. In addition, the specific endoglucanase gene of G362 Bacillus sp. can be identified through molecular methods and used for further research including structural studies. It may even be used as a protein template in protein engineering.

The development of rapid and highly sensitive diagnostic methods has received significant attention. Enzymatic nanobiosensors are a promising approach, offering fast results based on specific interactions between nanoparticles, enzyme, and target molecules. This study investigated the potential of ZnO nanoparticles, SnO, and multiwall carbon nanotubes (MWCNTs) as marker molecules in a system using beta-galactosidase enzyme for bacterial detection. Following nanoparticle synthesis, their structure was confirmed using XRD, FTIR, UV-DRS analyses. Enzyme activity was evaluated in the presence of the substrate ONPG. Different nanoparticle concentrations were tested with a constant amount of enzyme to determine the optimal concentration for inhibiting lactase activity. Subsequently, varying concentrations of Escherichia coli were introduced, and the ability of each nanoparticle type to detect bacteria was compared. Due to their small size, high surface area, and strong reactivity, these nanomaterials demonstrated the potential to detect low  bacterial concentrations in the environment.Bacteria likely attached to the nanoparticles, hindering their intraction with the enzyme and consequently affecting enzyme activity. The results revealed MWCNTs to be most effective for bacterial identification, detecting as low as 10 CFU/mL bacteria within 15 min. This approach has promising applications in the food industry for rapid detection of low-level bacterial contamination.