فصلنامه زیست شناسی میکروارگانیسم ها
پیاپی 42 (تابستان 1401)

Magnetic nanoparticles have various biomedical applications such as cell therapy, tissue repair, drug delivery, and magnetic resonance imaging (MRI) due to their unique physical, chemical, thermal, and mechanical characteristics as well as their suitable surface properties. The present study aimed to synthesize magnetic Fe3O4 nanoparticles (NPs) using the interaction of cell-free extracts of endophytic bacterial isolates with Fe2O3 as the precursor of NPs.

In this study, the extracellular synthesis of Fe3O4 NPs was accomplished by the cell-free extract (CFE) strategy. Characterization of Fe3O4 NPs was performed using different methods, including ultraviolet–visible spectroscopy (UV–Vis), field emission scanning electron microscope (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR).

The obtained results of the study showed that the precursor Fe2O3 could be transformed into Fe3O4 NPs with the endophytic strain BR06. Phylogenetic analysis indicated that the isolated strainBR06 belonged to the genus Bacillus, and shared the highest sequence similarity with B. siamensis (MT052693). The Fe3O4 NPs with average diameters of 34 nm and cauliflower shape were synthesized by the endophytic strain BR06 in the biotransformation medium containing 5 mM Fe2O3 after 24 h incubation time. Electron microscopy and the associated spectroscopic analyses confirmed the formation of Fe3O4 NPs.

In the present study, for the first time, the biosynthesis of extracellular magnetite NPs was described using B. siamensis under the cell-free extract strategy.

Microbial strain immobilization has some benefits like the repeatability and cost-effectiveness of strain recovery in the fermentation process. The present study aimed to investigate the effects of Aeromonas hydrophila MSB16 immobilization on its protease production.

The best method for immobilizing MSB16 was selected using five different polymers including alginate, alginate-polyvinyl alcohol, alginate-polyvinyl alcohol-calcium carbonate, alginate-γ-Al2O3 nanoparticles, and carboxymethylcellulose. The best immobilization method was selected based on the ability of protease production of immobilized cells through the one-factor-at-a-time approach. Then, the selected method was optimized using the surface response methodology (RSM). Finally, the data were analyzed by Design Expert 11 software and the analysis of variance.

According to the results of RSM, the immobilized strain in a polymer containing 3% alginate - 3% polyvinyl alcohol - 3% calcium carbonate showed the highest protease production (205/32 U/mL). The second-order model was statistically significant based on the F-values ​​(25.95) and p-values (0.0001). The high determination coefficient (0.9584) and the non-significance lack of fit (0.7818) confirmed the accuracy of the model. The MSB16 protease production was affected by calcium carbonate and polyvinyl alcohol concentrations and had an inverse relationship with calcium carbonate.

The statistical optimization of the MSB16 immobilization method led to a 2.13-fold increase in its protease production than the free cells.

Actinomycetes are filamentous and gram-positive bacteria living as free-living, saprophyte, and sometimes in symbiosis with plants. These bacteria could be isolated from all ecosystems including soil, water, marine sediments and especially hot waters. Marine actinobacteria are known as the producers of a vast range of secondary metabolites. Any actinobacterial strain has the genetic potential for the production of 10-20 of the secondary metabolites. About 23000 antibiotic types were discovered from microorganisms which according to the estimations, about 10000 types have been isolated from actinobacteria. The secondary metabolites produced by marine actinobacteria have an extensive range of biological activities such as antibacterial, antifungal, anti-cancer, cytotoxic, cytostatic, ant-inflammatory, anti-parasite, anti-malaria, antiviral, anti-oxidant and anti-angiogenesis, etc.

In the present study, water and sediment samples from the Persian Gulf at the Bushehr Atomic Energy Beach were collected for Actinobacteria isolation. For the cultivation of these samples, 7 culture medium types were used. For the identification of the gathered isolates, morphological properties, biochemical tests, and molecular studies (e.g. PCR) were investigated.

Twenty-four isolates of Actinobacteria were isolated from water and sediment samples of the Persian Gulf coast. Eighteen of the isolates have antibacterial activities. Seventy-five persent of the isolates were antibiotic producers and 95% of the gathered substances from these 18 strains had an antibacterial effect against gram-positive bacteria and 60% against gram-negative bacteria. Also, 60% of these substances were effective against both bacteria groups.

The abundance of marine actinobacteria in new sources of the Persian Gulf and the extension of this sea’s coat indicates the potential capability of this source for investigation in the scope of attaining new antibiotics.

Biological soil crusts including cyanobacteria, fungi, bacteria, actinomycetes, algae, viruses, mosses, lichens, and plants are formed on the soil surface. Cyanobacteria are key microorganisms in the formation of the biological soil crust, especially in arid and desert areas. Cyanobacteria increase carbon and nitrogen content in soil via increasing colony formation and Exopolysaccharide (EPS) production and play an important role to strengthen soil structure especially in poor soil and prevent it from eroding.

In the present study, three cyanobacteria with the highest secreted carbohydrate production were selected among 19 isolates of different provinces’ soil. The amount of carbohydrate production of the selected strains was determined by using the phenolic sulfuric acid method. Then, three selected strains, with the highest amount of secreted carbohydrate were inoculated to the pot filling with poor soils. After 7 weeks of cyanobacterial inoculation, some physical and chemical alterations of the soil were measured. Furthermore, the rate of formation of the biological soil crust and the adhesiveness of the soil particles were microscopically investigated.

The carbohydrate content was 86.66 µg/ml for Anabaena sphaerica, 55. 91 µg/ml for Geitlerinema.sp, and 64.19 µg/ml, for Nostoc pruniforme. The results of the study also show that these three strains are capable of forming biological soil crust on the soil surface.

Anabaena sphaerica, due to its high growth rate, more biomass production, and more secreted carbohydrates increased soil nitrogen and carbon content, as well as better formation of biological soil crust was selected for further investigation. This strain improved some soil texture characteristics and probably it can have a positive effect on soil fertility.

Although there are different methods for the production of nanoparticles, today the synthesis of nanoparticles with biological methods has attracted the attention of researchers because it is an easy, environmentally friendly, and cost-effective method. The present study investigates the biosynthesis of gold nanoparticles using Lactobacillus paracasei (MN809528) exopolysaccharide and studies the antibacterial, anti-biofilm, and antioxidant properties.

For the synthesis of gold nanoparticles, 30 ml of 1% exopolysaccharide (0.1 g) solution was added to an equal volume of 1 mM aqueous HAuCl4 solution and mixed well using stirred (180 rpm) for 48 h at room temperature. The characterization of synthesized gold nanoparticles was performed using UV-VIS, FT-IR, DLS, XRD, EDX, FE-SEM spectroscopic analysis. Antibacterial activity of produced gold nanoparticles by agar well diffusion method, anti-biofilm activity by 96 well microplate dilution method, and antioxidant activity of nanoparticles using DPPH radical adsorption capability were examined.

Spectroscopic data showed the presence of a peak at 524 nm, which is specific to gold nanoparticles. Examination of the shape and size of nanoparticles with FE-SEM showed that the produced nanoparticles were spherical in shape and their average size is 2o-50 nm. Antibacterial activity of gold nanoparticles at a concentration of 50 µg /ml was observed against all bacterial tests. However, the highest antibacterial activity was observed against Acinetobacter baumannii (ATCC 17978). In the present study, the gold nanoparticles produced acted as biofilm and DPPH radical inhibitors.

The results of the study show that Lactobacillus paracasei (MN809528) is a good biological source for the synthesis of gold nanoparticles. The study is the first report on the production of gold nanoparticles by exopolysaccharides isolated from indigenous lactic acid bacteria.

L-asparaginase is a significant anticancer enzyme used both in medicine and food industries. Considering the importance of L-asparaginase in different industries, finding new sources of producer strains that can produce higher levels of this enzyme with minimum side effects is preferred.

Initial screening for L-asparaginase-producing strain was performed via qualitative plate assay on modified Czapex Dox's agar medium using L-asparagine as the nitrogen source and phenol red as pH indicator. L-asparaginase activity of the fungal strain was quantified by the nesslerization method. Its identification was performed by using both morphological characteristics and phylogenetic analyses of DNA sequence data, including ribosomal DNA regions of ITS (Internal Transcribed Spacer) and LSU (large Sub-Unit) rDNA. L-asparaginase production was optimized by the One Factor-At-the-Time (OFAT) technique. The impacts of temperature, inoculum size, nitrogen, and carbon sources on the enzyme production were then evaluated.

Sarocladium kiliense IBRC-M 30453 was isolated from soil and identified as a potent enzyme-producing strain. The enzyme production was based on the extracellular mode. An optimum enzyme activity of 62.4 U ml−1 was obtained at the temperature of 25°C with inoculum size of 9% (v/v) and sucrose containing carbon and ammonium chloride as the nitrogen source. The optimization process led to 2.8-fold increase in the enzyme production.

There is a market demand for an alternate source of L-asparaginase with fewer adverse effects due to an increase in the clinical and industrial applications of this enzyme. Fungal L-asparaginase can be the proper answer to the current status of the market. However, application of statistical optimization processes and genetic manipulation have been recommended in other studies to achieve its maximum production level and improve feasibility of its industrial production.