فصلنامه دنیای میکروب ها
سال دوازدهم شماره 4 (پیاپی 41، زمستان 1398)

Dissolution of chalcopyrite is one of the most important challenges of hydrometallurgy because it is difficult to leach due to its inactivation by passive precipitates like jarosites. The combination of the benefits of microbial leaching (three strains of native mesophiles, moderate thermophiles, and extreme thermophiles), and chloride leaching was the main purpose to enhance the copper recovery, especially from the low-grade chalcopyrite sources.

The native microorganisms were isolated from Sarcheshmeh mine, and adapted (4 months with chloride media). Then, the bioleaching operation was systematically performed using the columns containing low chalcopyrite ore (less than 0.3% Cu) to investigate the effect of the chlorine on the bioleaching process. Different analyzes of the leaching and feed residues were used to closely examine the process and mechanisms involved (A 23% increase in recovery (81% with chlorine and 58% with no chlorine)).

Based on the analyses of the bio-leaching residues, overcoming the problems caused by the unwanted precipitates like jarosite during chlorinated bioprocess (2 g / l chloride) was one of the main reasons for these results which were identified using SEM, EDS analysis. And, the elemental mapping of the solid residues from microbial leaching operations proved this possible reason.

Controlling the undesirable precipitates in the process was the most important lever to improve copper recovery (more than 81% of copper over 120 days). This was achieved by regulating the growth process and activity of microorganisms from mesophiles to extreme thermophiles with sodium chloride salt additive.

Human growth hormone (hGH) or somatotropin is a single chain polypeptid which consisting of 191 amino acid residues and molecular weight of 22kDa. Overexpression of hGH in Cytoplasm often results in forming inclusion bodies (IBs). Purification process of hGH from IBs needs refolding process in order to obtain native protein that is complicated and often does not have good efficiency. Therefore, the high expression of soluble form is always considered.

In this study, recombinant E. coli-pET32a(+)-Trx-His6-hGH was used. In order to obtain high level production of soluble hGH in cytoplasm was used from Trx tag and for purification process of hGH was used from His tag. The bacteria was grown in LB and TB culture media at 25 ⁰C. The purification process carried out based on affinity chromatography using Ni-NTA resin.

The SDS-PAGE analysis showed 55% hGH expression that 33.7% expressed as soluble and 18.8% expressed as IBs. The amount of hGH fusion protein purified through Ni-NTA column was 22. 4 mg per gram of wet cells.

The results of this study indicate that hGH-Trx fusion protein was properly expressed. The purity of hGH fusion protein purified by histidine-tagged protein purification method was determined 91% with the total yield of 38%.

Ferric iron that commonly exists in leaching solution needs to be removed before the recovery of copper bioleaching using methods such as jarosite seed. The objective of this study was to investigate in the catalytic performance of biological seeds and Acidithiobacillus ferrooxidans in the process of jarosite formation via biosynthesis process.

Acidithiobacillus ferrooxidans was first grown in 9K medium. Jarosite seeds were synthesized using this bacterium. Then the effect of biological activity of different seeds (5, 10 g/L) on jarosite formation was investigated. The type of jarosites synthesized was identified by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) analysis. Meantime, the morphologies of jarosite crystals were studied.

The FTIR and XRD results showed that biosynthetic jarosite seeds is ammonium jarosite type. The amount of jarosite increased with increasing seed concentration and the induction time of precipitation decreased. The pH and Eh of culture medium with increasing seed decreased. Bacterial growth also decreased in the presence of jarosite seeds compared to medium without biological seeds. According to the results of SEM, The morphologies of ammonium jarosite crystals were significantly affected by the jarosite seeds. The jarosite crystals were precipitated with the presence of seeds had smooth, uniform and larger surface than non- seeding jarosite.

The results showed that the precipitation process of jarosite is more complete with biological seeds.  The results of this study can improve the efficiency of iron removal process in copper bioleaching and reduce production costs.

Azospirillum comprises rhizobacteria that live freely in the soil where they change gaseous nitrogen to nitrite and nitrate and as a result promote growth and yield of some economically important plants. The aim of this study was to isolate and identify different native species of Azospirillum and to investigate their genetic diversity as plant growth promoting factors.

In this research, some soil and root samples from wheat and maize fields of Isfahan province were collected and cultured in the tubes containing nitrogen free bromothymol blue (NFB) semisolid media. The Azospirillum isolates were chosen on the basis of morphological properties on NFB and RC (Rojo Congo) media and then were purified. The detection and identification of Azospirillum isolates was done by molecular tests using PCR (Polymerase Chain Reaction), 16S rRNA gene sequencing and genomic fingerprinting with rep-PCR (repetitive extragenic palindromic elements-polymerase chain reaction).

The replication of 646 and 263 bp fragments by Az16S-A, Azo494-F/Azo756-R primers respectively, confirmed the presence of Azospirilum bacteria. Azospirillum species were also identified as A. brasilense, A. lipoferum and A. zeae using replication and sequencing of 16S rRNA gene. The genomic profilings of different Azospirillum isolates produced unique band patterns through application of repetitive element BOX (BOX-AIR), ERIC (ERIC IR, ERIC 2: Enterobacterial Repetitive Intergenic Consensus) and REP (REP IR, REP 2: Repetitive Extragenic Palindromic) and showed high genetic diversity between the isolates.

Tomato big bud is a phytoplasma disease which has been recently distributed in different areas of Iran. The aim of this study was to determine the concentration and distribution pattern of 'Candidatus Phytoplasma aurantifolia' within tomato plants for its rapid detection, especially during the incubation period of the disease.

Three tomato plants were graft-inoculated with 'Candidatus Phytoplasma aurantifolia' in a factorial experiment in a completely randomized design. At the time intervals of 10, 20, 40 and 70 days post-inoculation, samples of apical leaves, leaves above and below the grafting site and lateral roots were taken from the inoculated plants. The concentration of the phytoplasma and its distribution pattern were evaluated using real-time PCR. In addition, the direct and nested-PCR assays were used and compared for detection of 'Candidatus Phytoplasma aurantifolia'.

The current study found that after entrance into the tomato plants, 'Candidatus Phytoplasma aurantifolia' moved upward into the apical leaves as well as downward into the roots. The phytoplasma concentration in the apical leaves and roots was higher than the leaves of the middle and lower branches of the inoculated plants. The mean of disease incubation period was estimated to be about 40 days. The nested-PCR was more sensitive than direct-PCR in detecting the phytoplasma.

For the detection of tomato big bud disease associated with 'Candidatus Phytoplasma aurantifolia', especially during the incubation period of the disease, it is recommended to sample form apical leaves and roots as well as using nested-PCR.

One of the most significant current discussions is approaching the antibacterial activity of essential oil to control plant pathogenic agents. Current study aimed to characterize chemical composition and antibacterial activity of Foeniculum vulgare and Eucalyptus to control some plant pathogenic bacteria in-vitro. In the present study, essential oil components of Foeniculum vulgare and Eucalyptus were subjected to Gas chromatography–mass spectrometry analysis, their minimum inhibitory concentration and antibacterial inhibitory on some plant pathogenic bacteria were determined. GC-MS analysis showed that the main component of the essential oil of F. vulgare were p-cymene, (30.18%), Cuminal (24.74%), 2-beta pinene (11.81%), while Eucalyptus were 1,8 cineol (47.87%), 1-alpha pinene (17.94%), p-cymene (7.91%) and Limonene (7.68%). Also, minimum inhibitory concentration was 3.79 µg/ml and 8.54 µg/ml for F. vulgare and Eucalyptus, respectively. Results of the antimicrobial investigation demonstrated that F. vulgare had the highest inhibition diameter of 4.4 centimeters in Clavibacter michiganensis. In Eucalyptus essential oil, highest inhibition zone (4.3 centimeters) were attributed to Erwinia amylovora. Results showed that by increasing the concentration, antibacterial activity increases. Our findings provide a rational basis of a novel emerging alternative to antimicrobial treatments in plant disease management programs.

Bdellovibrio-and-like organisms (BALOs) are a group of predatory bacteria which invade other Gram-negative bacterial cells for growth. The bacteriolytic nature of Bdellovibrios make them one of the promising alternatives for conventional antibiotics. In this study, the isolation and molecular identification of Bdellovibrio bacteriovorus strain SOIR-1 was described. The antibiotic resistance pattern of some clinically isolated Gram-negative pathogens was determined, and the predatory potency of SOIR-1 toward them was evaluated.

Double-layer agar technique, transmission electron microscopy, and PCR targeting the Bdellovibrios-specific hit locus were used for the isolation, morphological investigation, and molecular identification of SOIR-1, respectively. Following the antibiotic resistance profile determination of clinical isolates, the bacteriolytic activity of SOIR-1 against them was evaluated through the plaque formation assay and lysis analysis in the broth co-cultures.

SOIR-1 was identified as a strain of Bdellovibrios bacteriovorus through the transmission electron microscopy examination and specific PCR detection. All clinical isolates showed the properties of extensively drug-resistant (XDR) and typical Bdellovibrios plaques were developed on their lawns of cells. The SOIR-1 had the highest and lowest predation efficiency among the clinical isolates toward Acinetobacter baumannii (84.33%) and Pseudomonas aeruginosa-369 (55.16%), respectively.

This study highlights the great potential of SOIR-1 to prey and lyse XDR pathogens, regardless of their antimicrobial resistance state. So, B. bacteriovorus can be considered as a living antibiotic in the cases of infections caused by multidrug-resistant bacteria.

Biosurfactants are biological surface active compounds produced by fungi, yeast and bacteria. These amphiphilic compounds can reduce surface tension and interfacial tension between individual molecules. The aims of this investigation was screening of biosurfactant producing halotolerant Actinobacteria species from the unexplored regions of Qom saline lake.

About 110 soil actinobacteria isolated strains were initially screened and then teste for their ability to BS production. Conventional screening methods of BS carried out using blood hemolysis, drop collapse method,oil spreading and surface tension measurements. 16S rRNA sequencing was done for the best biosurfactant producer strain. Further the partially purified BS was characterized by TLC, FTIR and compositional analysis. BS production was optimized using different carbon & nitrogen sources and optimized by different culture conditions such as temperatures, pH and stirring rate.

15 out of 110 isolates were able to tolerate high salt concentrations up to 10% . 8 isolated strains were BS producer. Isolate No.9 showed 99% similarity to Microbacterium paraoxidans by 16S rRNA gene sequencing method. Compositional analysis methods proved a glycolipid structure of BS. Sucrose and yeast extract were identified as the most appropriate carbon and nitrogen source, respectively. Maximum production of BS was obtained in pH 7,at temperature 27 oC and stirring rate 170 rpm.

These findings emphasize that such bacterial strains with superior BS production may find their potential application in bioremediation marine and soil ecosystem.