فصلنامه زیست شناسی میکروارگانیسم ها
پیاپی 5 (بهار 1392)

In biological production of low value added bioproducts، the substrate cost comprises a significant part of the total price. Therefore، choosing an inexpensive substrate with a high yield of production can greatly reduce the production cost. Starch as an abundant and cheap carbon source can be a suitable substrate for microbial production of xanthan gum. However، in most of the studies on microbial xanthan gum production، glucose has been used as substrate. Materials and method s: In this study، microbial production of xanthan gum using Xanthomonas campestris PTCC 1473 and hydrolyzed starch as carbon source was investigated. The concentration of carbon source and time were optimized using RSM-CCD method. Both factors were regarded to be significant for production of xanthan using hydrolyzed starch.

Based on the obtained results، optimum carbon source concentration and time were 56 g/L and 38. 4 h، respectively. Under optimum conditions، 8. 34 g/L of xanthan gum was produced. Discussion and

The results of this study indicated that starch could be used as a waste and inexpensive carbon source instead of glucose for the production of xanthan gum. It was also shown that the effect of carbon source concentration was more significant than time for xanthan production. In addition، these two factors were independent and did not have any interaction.

Probiotics have some beneficial effects on health so these microorganisms are added to dairy products and other foods as well. Lactobacillus bacteria are the most commonly used for this purpose. The aim of this study was to find native Lactobacillus bacteria which has the potentiality for using as probiotic. For isolating lactobacilli، gram strain reaction and catalase test were performed on separated bacteria from 40 local yoghurt samples: after isolating، the acid resistance ability of isolates were evaluated by placing isolates in pH=2. 5 for 2 hours and culturing samples on medium and colony counts. Then، among 18 acid resistant bacteria، by gel diffusion method the inhibitory effect of isolates on pathogens bacteria such as E. coli and Pseudomonas aeruginosa were investigated. The results were compared to the results of investigated commercial strains. The results revealed that S4 isolate had the most inhibitory effect، it showed %80 good-inhibitory and %20 strong-inhibitory effect on pathogenic bacteria، which were completely consistent with results for commercial Lactobacillus gasseri strain. Also، the lowest inhibitory effect against pathogens was related to (Y4-Y5-Y11-Y14-Y15) isolates that all of them had weak-inhibitory effect on pathogens. Other strains were classified in good-inhibitor group. Discussion and Considering daily increasing of drug resistance relating to pathogenic bacteria، today، the use of probiotics، especially lactobacilli as an appropriate alternative of antibiotics is important. The investigated bacteria in this study were able to inhibit pathogens’s growth to some extent، but for investigating the results more accurately، some methods with more sensitivity، for instance، two layers method and MIC method can be used as well.

Ciprofloxacin is a fluoroquinolone antibiotic which is active against mycobacteria and functions by inhibiting DNA gyrase and topoisomerase IV enzymes. Resistance to ciprofloxacin and other fluoroquinolones may evolve rapidly، even during a course of treatment. Nowadays، mycobacteria exhibit resistance worldwide and usage of the fluoroquinolones، particularly in nontuberculous mycobacteria disease، has complicated the related treatments. A total of 39 clinical and environmental isolates of NTM from microbial collections of Isfahan Microbiology Department and Tuberculosis center were obtained. The isolates were investigated by primary conventional methods consisting of colony characteristics، pigmentation، growth temperature، rate of growth and Ziehl–Neelsen staining. The susceptibility of isolates to the concentrations of 1، 2 and 4 µg/ml of ciprofloxacin was determined by agar dilution method according to the CLSI guideline. Thirty nine isolates were identified by phenotypic tests. The frequency of isolates was as follow: M. fortuitum; 25 cases، M. gordonae; 10 cases، M. smegmatis; 1 case، M. conceptionense; 1 case and M. abscessus; 2 cases. All isolates except Mycobacterium abscessus were sensitive to all three concentrations of 1، 2 and 4 µg/ml ciprofloxacin. Discussion and Due to the sensitivity of environmental nontuberculous mycobacteria isolates (except M. abscessus) and clinical isolates including M. fortuitum and M. gordonae to ciprofloxacin، this antibiotic could be regarded as the original drug in the treatment of these infections.

The use of resistant bacteria to radiation and other extreme conditions for bioremediation of the environmental and radioactive waste is very important due to their survivability and catalytic efficiency under high stress conditions. After primary and secondary screening by irradiation with UV lamp، one isolate was obtained and identified on the basis of morphological and biochemical characteristics، 16S rRNA gene sequencing and phylogenetic analysis. In the next step، the isolate was exposed to extreme conditions such as: UV-radiation (25J/cm2)، desiccation (28 days)، %1-5 hydrogen peroxide، mitomycin C (1-8µg)، salinity (%5-25 NaCl) and different pHs (pH 1. 0-11) during or after culture in TGY medium. Bacterial growth or survival was analyzed by spectrometry or flow cytometry. Isolated strain MG6 was an ultraviolet-resistant، Gram-positive، and rod shaped bacterium that its 16S rDNA sequences showed %99. 69 similarity with Microbacterium resistens. This similarity was confirmed by phylogenetic analysis. Optimal growth rate of strain MG6 occurred at pH 5، %5 (w/v) NaCl and tolerated %1- 4 H2O2 and 2µg of mitomycin C. Analysis of viability indicated that this strain had highly resistance to UV-C radiation but moderately resistance to showed desiccation. Discussion and In this study، a new strain of M. resistens was isolated which was UV-resistant and showed tolerance to several extreme conditions such as: low pH، oxidant and mutagen agents، salinity and desiccation. The UV resistance of strain MG6 was comparable with Deinococcus radiodurans R1. This research was the first study on multiple extreme resistance of M. resistens new isolated strain (MG6) in Iran. Also this strain could be a candidate for the future researches such as bioremediation of radioactive waste sites.

With respect to the usefulness of lichens in the traditional medicine in different parts of the world، identification of lichens and studying their antimicrobial effects are of particular importance. After collecting lichen samples، the methanol extracts were prepared and the effects of dilutions extracts on six pathogenic bacteria to method disc diffusion and the antibiotic Methicillin، Clindamycin، Sterptomycin and Ampicillin were compared to a positive control. Then، the MIC and MBC were determined. Diameter investigation showed that acetone extract of the lichen on the bacteria did not have any affect. Methanol extracts of lichens Fulgensia fulgens (Sw.) Elenkin had significant antibacterial activity. Discussion and Among the lichens we studied، only Fulgensia fulgens had. Therefore، the methanol extracts of Fulgensia fulgens could have antibacterial effects in the treatment of bacterial infections and thus could be replaced by chemical drugs.

The endophytic bacteria are group of bacteria، which live in plants tissues without any apparent harmful effects to the plants. Recently they have been isolated from different parts of plants with capability to produce anti fungi or bacterial activity. Nowadays، the endophytes instead of the fertilizers and germicidal chemical substances are used in agriculture hence the present study evaluated the presence of these organism in Glycine sp. in order to investigate their possible antifungal metabolites. First، in the present study، endophytic bacteria were isolated from the stems and leaves of soybean using serial dilutions on the brain heart infusion agar. Then، the isolates were evaluated for ability to produce anti microbial metabolites against two fungal pathogens: Alternaria alternate (PTCC 5224) and Fusarium solani (PTCC 5284) based on parallel streak and well diffusion agar methods. The bacterial strains with ability to produce antimicrobial metabolites were identified using Api 20E، 20NE kites and then their growth curves were studied. Totally، 39 bacterial endophytes were isolated from stem and leaves of the soybean plants among wich 20 belonged to the stems and 19 were isolated from the leaves. Among، all bacterial isolates 3 showed the antimicrobial effect which identified with Api kits and they belonged to the genus of Pseudomonas. Among the bacteria with anti microbial activity Pseudomonas aeroginosa was the most effective on the fusarium solani. In addition، the results obtained from the growth curves of the bacteria indicated that most of the microorganisms produced their compounds at the first 18 hours which was continued up to 72 hrs in some isolates. Discussion and The present study showed that soybean plant containing endophytic bacteria had the ability to produce antimicrobial effect against plant pathogens and that the produced compounds can be used in further researches.