فصلنامه زیست شناسی میکروارگانیسم ها
پیاپی 38 (تابستان 1400)

Today, one of the main environmental problems is hydrocarbon pollution due to the activities of oil and petrochemical industries. Accidental oil spills occur in the environment during the exploration, production, transportation, and storage of petroleum products. Technologies commonly used for soil remediation are expensive and can lead to the incomplete degradation of pollutants. Biodegradation is a cost-effective technology for the recovery of oil-contaminated areas.

This study was conducted to isolate crude oil degrading bacteria, soil, and sludge from seven oil-contaminated areas in Masjed Soleyman. To determine the frequency of heterotrophic and degrading bacteria, the bacteria were counted by the serial dilution and MPN methods. Twenty-four strains were isolated by the culture enrichment method in Bushnell-Haas broth medium containing 0.5% crude oil. Then, based on warm staining and colonial characteristics, oil spreading test, cell surface hydrophobicity, and the emulsion activity of the strains were examined for initial screening. Finally, the top 10 strains were screened by spectrophotometric and gravimetric methods with a concentration of 0.5% crude oil. Also, Gas Chromatography (GC) was performed on the superior strain.

The identified strains belonged to the genus Rhodococcus jostii strain D3 and Arthrobacter citreus strain E3. The top two strains were studied to investigate the effects of different concentrations of crude oil, nutrient effects, time effects, and mixed culture. The highest oil expansion was related to F3 strain and the highest emulsion activity rate was related to E3 strain. D3 strain with 41% degradation at the concentration of 4.5 and E3 strain with 73.5% degradation at the concentration of 1.5 showed the best results in response to different crude oil concentrations. The results of gas chromatography analysis confirmed that strain D3 can degrade 95 percent of crude oil at the concentration of 0.5%.

The identified strains have a great potential in removing hydrocarbon pollution and can be used at the field level to reduce and eliminate oil pollution in the contaminated areas in the future.

Klebsiella pneumoniae is a human opportunistic pathogen. Biofilm formation is one of the important properties of this bacteria that leads to the development of multidrug-resistant phenotypes. In recent years, Nanoparticle Technology (NP) has been an important field in a wide range of studies. In this study, the effects of chemical nanoparticles on biofilm formation and antibiotic resistance of Klebsiella pneumoniae were investigated.

Overall, 340 samples from patients were collected from different hospitals in Tehran. Colonies were tested to identify bacteria based on standard techniques. In each bacterium, the presence of important biofilm formation genes in Klebsiella pneumoniae was detected by Multiplex PCR and their expression levels were analyzed using the Real-time PCR method. The effect of chemical nanoparticles of iron oxide on biofilm formation and antibiotic resistance was also investigated.

Sixty isolates of Klebsiella pneumoniae were identified based on standard techniques. The results showed that both types of iron oxide nanoparticles had a significant effect on inhibiting the formation of biofilm and antibiotic resistance of this bacterium (p <0.001). In addition, the combination of iron oxide nanoparticles and ciprofloxacin had significant antimicrobial effects compared to other compounds (p <0.001).

The formation of biofilm and the antibiotic resistance of Klebsiella pneumoniae isolates were effectively inhibited in response to iron oxide nanoparticles. The results could be useful in controlling multiple drug-resistant infections in hospitalized patients.

Arbuscular Mycorrhizal Fungi (AMF), as the most abundant mutual symbiotic association between fungi and plants in the soil, are of great ecological and economic importance. The present study aimed to identify AMF species associated with different plant roots based on morphological and molecular characteristics of ß-tubulin gene sequences of collected samples in Raviz and Daveran regions of Rafsanjan city.

Samples were collected from the rhizosphere of different plants and AMF spores were isolated from the soil samples using the wet sieve method. The identification was performed based on morphological characteristics of the spores such as the color, shape, surface ornamentation, size, wall structure as well as characterization of the spores in water. The DNA of the fungi was extracted from single spores and partial sequences of ß-tubulin gene were amplified by three nestedPCR using appropriate primers. The PCR products of the selected samples were sent for Sanger sequencing. The phylogenetic relationship of the selected sequences with other available isolates in GenBank was analyzed using the Maximum likelihood method.

Based on morphological characteristics and phylogenetic analysis of the partial sequence of ß-tubulin gene, the following species were detected: Funneliformis mosseae, Funneliformis coronatum, Gigaspora gigantean, Scutellospora calospora, andSeptoglomus constrictum. F. mosseae followed by F. coronatum were recognized as the dominant species in the present study.

The partial sequence of ß-tubulin gene was well separated from the studied orders, families, and genera of arbuscular mycorrhiza fungi. All the identified species in this study were placed in the expected taxonomic level. The results of the molecular analysis confirmed the classification of species based on morphological characterization.

Diverse endophytic fungi exist within plant tissues that are valuable resources for plant growth promotion. These endophytes constitute a rich bio-resource to discover new natural products. Also, endophytic fungi have been recognized as useful sources of bioactive secondary metabolites including antibiotic, antioxidant and anticancer. This study to evaluate antioxidant activity and the phytochemical properties ethyl acetate extract of endophytic fungi from Corylus avellana L. plant. First, endophytic fungi were isolated from C. avellana plant using standard surface sterilization techniques. Ethyl acetate extracts of fungi were screened for the presence of characteristics of qualitative phytochemicals compounds and antioxidant activity. For this purpose, DPPH free radical scavenging was used to evaluate the antioxidant activity. The presence of phytochemical compounds, flavonoids, alkaloids, tannin, phenol, steroid, terpenoid, diterpene, flavanones, quinone and cumarin was also assayed qualitatively. In total, 791 isolates belonging to 24 species were isolated from the stem, leaf and root tissues. . All sequences were deposited in NCBI's GenBank Database. The qualitative analysis of phytochemical compounds showed positive results for flavonoids, alkaloids, tannin, phenols, steroids, terpenoids, diterpenes, flavanones, quinones and coumarins in most of the fungus. Species Paraphaeosphaeria sporulosa, Cladosporium herbarum, Alternaria alternate, Nothophoma quercina, Fusarium equiseti, Pleosporales sp., Neocucurbitaria unguis, Penicillium citrinum, Fusarium sp., Fusarium fujikuroi, Epicoccum nigrum, Gnomoniopsis idaeicola, Cladosporium sphaerospermum, Bjerkandera adusta, Angustimassarina sp., Exophiala sp., Talaromyces amestolkiae showed the highest antioxidant activity ranging from 50% to 97%.Hazelnut plants have different fungal endophytes with several antioxidant activities. Phenoles and flavonoids were positive in all fungal extracts and are the most important phytochemical compounds in this study. Extracts with more phenoles and flavonoid contents produced more antioxidant activity. The results of this study represent that metabolites produced by endophytic fungi isolated from C. avellana plant may serve as a potential source of natural antioxidants.

Phytophthora nicotianae is a destructive plant pathogen with a worldwide distribution that causes root, fruit, leaf, and crown rot. Phytophthora species are the main reason for various diseases in a wide range of plant species including vegetables. Symptoms include fruit, stem, crown, and root rot. They lead to plant host death and in most cases, the economic losses caused by P. nicotianae are very high due to the diversity of the host range and its damage, therefore, controlling this pathogen is a constant challenge.

In order to biologically control the disease, three Streptomyces isolates including M6, M8, and M215 were selected from a large number of soil-inhabitant actinomycetes isolated from Kerman province, which showed effective anti-Oomycete activity against P. nicotianae. To better understand the inhibitory mechanism of these isolates, in vitro dual-culture assay, plant growth promotion, and pathogen control effects were investigated through the application of antagonists under laboratory and greenhouse conditions. Molecular identification of the most promising isolate was also achieved.

The antagonistic activity of three isolates including M8, M6, and M215 against P. nicotianae in tomato plants (super chef variety) was evaluated. Among all, based on the statistical analysis under both laboratory and glasshouse conditions, the M8 isolate had an inhibitory effect on the crown and root rot of tomato. The comparison of the effects of antagonists on the tomato plant yield indices revealed that M8 isolate had the greatest effect on increasing the growth indices of the tomato plant (super chef cultivar) including plant height, the number of flowers, shoot, and root dry weight. The M8 isolate was identified by the sequence analysis of a small ribosomal RNA subunit (16S rRNA). Based on the results of the present study, Streptomyces venetus CMU-AB225T strain had the highest similarity (96.08%) with the M8 isolate.

The results showed that M8 isolate can be considered as a beneficial microorganism to produce some useful biofertilizers and bioactive materials to control tomato crown and root rot biologically. Some biocontrol agents such as T. harzianum and T. asperellum within composts can be effective in reducing the symptoms of Ph. nicotianae in pepper seedlings. The production of any product based on the S. venetus (M8) requires fulfilling further research steps such as the interaction of the bacterium with other beneficial soil microorganisms and its impact on the population of beneficial soil microbes, evaluation of the antimicrobial activity of M8 against other plant pathogenic fungi, fungal-like microorganisms and bacteria. Moreover, biosafety considerations and measures have to be investigated.

Environmental pollution with heavy metals is increasing with the development of the industry. The aim of the present study was to examine the isolation and molecular identification of chromium-resistant bacteria from contaminated wastewaters to investigate the bioremediation of chromium by them.

Chromium-resistant bacteria were isolated from tannery and leather factory effluents. The temperature, pH, BOD, COD, and the amount of heavy metals in each sample were determined. Bacterial isolation was performed by the agar dilution method in the presence of different concentrations of chromium from 1 to 128 mmolL-1. Then, the MIC and MBC for the selected strains were determined. The molecular identification of the resistant strains was done by colony PCR. The biological removal of chromium was evaluated by the selected strains under in vitro conditions.

The results of the study showed that the temperature, pH, BOD, and COD in the leather factory effluent were 28.7 ° C, 7.10, 100, and 330 mgL-1 and in the tannery effluent were 26.03 ° C, 6.84, 110, and 480 mgL-1, respectively. In this study, Bacillus subtilis H1F and Bacillus sp. H1D were isolated from leather wastewaters and Bacillus cereus H2C was the selected strain from tannery effluents. Among them, B. subtilis H1F showed the highest chromium resistance with an MIC value of 64 mM. Chromium removal of this strain was 68.5 ppm and it had the highest capacity among the three selected isolates.

Considering that B.subtilis H1F had the highest resistance and adsorption of chromium compared to other two bacteria, it is a suitable candidate for the biological removal of chromium from polluted effluents.