فصلنامه زیست شناسی میکروارگانیسم ها
پیاپی 8 (زمستان 1392)

Biodesulfurization is used as a selective method for lowering the sulfur content of petroleum products. Materials and method s: A sulfur-oxidation bacterial strain named Rhodococcus erythropolis R1 (NCBI GenBank Accession No. GU570564) was used in this study for desulfurization of dibenzothiophene (DBT). The induced culture of strain R1 was able to produce 2-hydroxybiphenyl (2- HBP) from DBT followed 4S pathway without further degrading carbon backbone. This process confirmed by gas chromatography (GC) analysis. The specific activity of DBT desulfurization by R1 was 45 µM (g dry wt)-1 h-1. The addition of Tween 80 as surfactant and glycerol as carbon source determines a 100% rate of DBT-desulfurization during 3 days. The heavy plasmid detected in R1 strain carries dsz genes responsible for biodesulfurization of DBT that was shown by PCR reaction. The mutant strains which had lost this plasmid also had lost desulfurization phenotype. Both mutant and wild strain were sensitive to high concentration of 2-HBP and some antibiotics. Discussion and Strain R1 desulfurize DBT through the sulfur-specific degradation pathway or 4S pathway with the selective cleavage of carbon-sulfur (C-S) bonds without reducing the energy content. Addition of surfactant enhanced the desulfurization of DBT by increasing its bioavailability and also could improve the growth and desulfurization rate. The location of desulfurization genes was on a heavy plasmid in strain R1. Based on the results of this study, R. erythropolis R1 could serve as a model system for efficient biodesulfurization of petroleum oil without reducing the energy value.

Staphylococcus aureus is an opportunistic pathogen in dairy ruminants which is also found in healthy carriage and can be a major cause of mastitis. Various mastitis control programs have been used to combat the problem but have not always been efficient. In most countries, antibiotic resistance is extremely common. Silver nanoparticles have shown antimicrobial activity against S. aureus. In the present study the effect of silver nanoparticles on S. aureus isolated from cattle mastitis along with antibiotics of operative on protein bacterial synthesis investigated. Three hundred eleven milk samples were collected from the cow farms. Each milk sample was cultured on mannitol salt agar and was incubated. A total of 72 isolates of S. aureus were isolated from the bovine mastitis milk samples. S. aureus DNA extracted by DNA purification kit according to the manufacturer protocol. 58 isolates were confirmed as S. aureus by biochemical tests as well as nuc gene detection. MIC and MBC determined for silver nanoparticles with antibiotics on 50 isolates. The resistance of S. aureus isolates against erythromycin, gentamicin, streptomycin and doxycycline were 100, 22, 100 and 8%, respectively. 8 of all isolates were sensitive to 25 µg/ml concentration of silver nanoparticles. The 92% growth of the samples were inhibited at concentrations between 50-100 µg/ml. Discussion and The p resent study suggests that antibiotics which can inhibit protein synthesis have significant synergistic effect along with silver nanoparticles.

A variety of oxygen-transport and -binding proteins exist in organisms including bacteria, protozoans, and fungi all have hemoglobin-like proteins. In addition to dealing with transport and sensing of oxygen, they may also deal with NO2, CO2, sulfide compounds, and even O2 scavenging in environments. Also they detoxified chlorinated materials like P450 enzymes and peroxidases and use as a detector of nitrate and hydrogen peroxide. Pore-forming bacterial globins are interested for filtration. Although there are data for bacterial toxin as a filter, here we used Agrobacterial hem to induce nano pore in the heme structure using point mutation. Investigations showed that three amino acids leucine 76, alanine 83 and histidine 80 are important for pore formation in Agrobacterium hemoglobin. A point mutation on leucine 76 to glycine, histidine 80 to asparagine and alanine 83 to lysine step by step led to create the nano pore 0.7- 0.8 nm in the globin. Discussion and These mutations in bacterial hemoglobin increase the stability when mutation is with it’s at pH7. This mutation decreases the aliphatic index however increase the stability index.

Because their ability to capture CO2, photosynthetical microorganisms have some advantages to CO2 mitigation from high CO2 streams such as flue gases and they can use CO2 as carbon source. Recently, experts have made efforts to exploit microorganisms intended for recovering CO2 from power plants. Materials and method s: To achieve this purpose, we studied the growth response of the cyanobacterium Spirulina platensis PCC9108 under different concentrations of carbon dioxide (ranging from 0.036% to 10%) and flue gas in a bench-scale system. Preparation of different concentrations of CO2 and injection into Erlenmeyer flasks was performed by a system including air compressor, CO2 capsule, pressure gauge and flow meter. The main goal of studying this paper is a survey of organism's potential to grow by generated CO2 from flue gas of power plant. It already had the potential and highest biomass production recorded at 8% CO2 (v/v). Also we proved that S.platensis PCC9108 can be grown under flue gas, although biomass production decreased fairly. Total lipid content of algae interestingly enhanced with elevated CO2 levels from ambient air to 4% and 6% which ranged from 14.5 to 15.8 and 16 dry weight (wt.) % respectively. In contrast, total protein content illustrated no difference between all treatment and its value was about 46 wt.%. Discussion and The results of present study suggested that understudied S.platensis PCC9108 is appropriate for mitigating CO2 because of its carbon fixation ability. Also due to its high protein content, this cyanobacterium is a good candidate to produce SCP (single cell protein).

Plant growth stimulating rhizobacteria are beneficial bacteria that can cause resistance to various stresses in plants. One of these stresses is SO2 air pollution. SO2 is known as a strong damaging air pollutant that limits growth of plants. The aim of this study is evaluation of the effects of bacterial inoculation with native and standard Rhizobium on Persian clover root growth and antioxidants activity and capacity under air SO2 pollution. Materials and method s: In this study, 31 day s plants (no-inoculated and inoculated with two strains of Rhizobium) exposed to the different concentrations of SO2 (0 as a control, 0.5, 1, 1.5 and 2 ppm) for 5 consecutive days and 2 hours per day. Results showed different concentrations of SO2 had a significant effect on Persian clover root weight and antioxidant system. Increasing SO2 stress decreased root fresh and dry weight and antioxidant capacities (IC50) and increased antioxidant activities (I%) of Persian clover leaves significantly in comparison to the control plants (under 0 ppm) and increased SOD, CAT and GPX activity. Inoculation of Persian clover plants with native and standard Rhizobium increased root weight and did not show a significant effect on antioxidants activity and capacity, but interaction between Rhizobium inoculation and SO2 treatment reduced significantly the stress effects of high concentration of SO2 on root growth and antioxidants activity and capacity. In fact, level of this change of root growth and antioxidant system under SO2 pollution stress in inoculated plants was lower than in the non-inoculated plants. Discussion and As a result, an increase in SO2 concentration caused a decrease in root weight, increase in antioxidants activity and capacity of Persian clover. Inoculation with Rhizobium strains could alleviate the effect of SO2 pollution on antioxidant system by effects on root growth.

‏Medical devices are made from a variety of materials such as polypropylene, polycarbonate, poly styrene, glass and etc. by attaching to this surfaces, Acinetobacter baumannii can form biofilms and then cause several device associated infections. Biofilms are communities of bacteria attached to the surfaces. In this study, biofilm formation ability in clinical isolates of Acinetobacter baumannii was assessed by two method s on different surfaces. Biofilm formation by 75 clinical isolates of A. baumannii was evaluated on polycarbonate surface (microtiter plate) and polypropylene surface (falcon) by crystal violet and 2,3-Bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide salt (XTT tetrazolium sodium salt) assay methods. Falcon or tube method was carried out under static and agitation conditions. ‏Results showed the most isolates can form biofilm but higher numbers of isolates form biofilm on polypropylene surface under agitation. XTT method confirmed strong biofilm formation ability of 10 isolates. Discussion and Each of the two assays showed an excellent applicability for the quantification of biofilms. The Crystal violet assay is cheap, easy and is usually used for the quantification of biofilms formed by microorganisms but XTT is more reliable and repeatable. Most of A. baumannii isolates have potential to form biofilm on the medical devices which may result in device-associated infections.

Staphylococci release a large number of enzymes. Some of these, such as coagulase, beta lactamase, hemolysins and biofilms are considered indices of pathogenicity. The aim of the current study was based on the isolation and identification of Staphylococcus aureus and coagulase negative Staphylococci (CNS) strains from sheep sub clinical mastitis and examining their biofilm, beta lactamase, hemolysins production and antibiotic resistance pattern. 55 Staphylococci strains were isolated from seventy cases of sheep subclinical mastitis. Thirty three were determined as Staphylococcus aureus (60%) and 22 (40%) as CNS. The hemolytic activity was evaluated by plating Staphylococci strains on 5% bovine blood agar. The biofilm assay was performed by using micro titer plates. Beta Lactamase production was detected by test tube iodometric technique and susceptibility to antimicrobial agents was determined for isolated strains by the disk diffusion method. Twenty six (78.8%) S. aureus strains were biofilm producers. For CNS (59.9%) strains were positive in biofilm production. Two isolates (6.06%), of S. aureus were α, the same number β and 6 (18.2%) isolates were ∂ hemolysin producers. Six isolates of CNS (27.27%) were α and ten (45.45%) ∂ hemolysin producers. Sixteen S. aureus (48.5%) and five CNS (22.72%) isolates were positive in beta lactamase production. The isolated Staphylococci show a low sensitivity pattern to methicillin and streptomycin. Discussion and A high percentage of strains make α toxin that play a role in S. aureus biofilm formation. Twenty one out of 33 (63.63%) isolated Staphylococci were biofilm producers that can have deleterious effects because biofilm formation is thought to play an important role in the survival of virulent strains of Staphylococci. Sixteen out of 33 (48.5%) isolated S. aureus were positive in beta lactamase test, Excluding resistant to methicillin, all of these isolates show a marked sensitivities to other examined beta lactam drugs. High percentage of hemolysins, biofilm and beta lactamase production by isolated Staphylococci, suggest an important role of these virulence factors in the pathogenesis of isolated Staphylococci from mastitis sheep milk samples.