فصلنامه زیست شناسی میکروارگانیسم ها
پیاپی 30 (تابستان 1398)

Nowadays, gluconic acid and its derivatives usages have been broadening in food industry. However, there are still many studies to optimize the production of gluconic acid by fermentation methods. The main goal of the present study was to assess the influences of temperature and pH on some fermentation kinetic parameters and activity of total cellular dehydrogenase.

Acetobacter senegalensis was cultured in batch mode fermentation in different conditions (different concentrations of carbohydrates, temperatures and pHs). In addition, the effect of pH onsub-population formation and by-product production was studied by flow cytometry and different chromatography techniques, respectively.

Flow cytometric assessment showed that bacterial cells segregated during stationary phase, and two sub-populations were appeared based on the activity of total cellular dehydrogenases. Culture medium pH affected the sub-populations formation and the percentage of each sub-population. As culture medium pH decreased, higher percentage(up to 61% of inactive cells) were formed during stationary phase. In addition, it was proved that at low pH (4.5), the percentage of by-products such as keto-gluconic acids increased more than 6 times. Based on the obtained results, the optimum pH for A. senegalensis to ferment 95 g/L glucose to sodium gluconat at 38°C was 5-5.5.
Discussion and

Acetobacter senegalensis can be used as a potential microorganism to produce gluconic acid. However, cell segregation during fermentation seems to result in decreased active producing cells and decreased maximum glucose consumption rate. In future studies, it is necessary either to find a method to prevent cell population from segregation or to resuscitate them into functional cells.

Due to very small dimensions, nanomaterials can have different properties compared to their bulk form. In nanometer dimension of material, atomic behavior dominates. Such behavior changes may adversely affect biological organism, especially phytoplankton as the basis of food chain cycle. For this reason, in current research, toxicity of CuO nanoparticles (CuO NP) on Scenedesmus dimorphus has been evaluated. The average size of CuO NP used were 20 nm. 

The experiments were conducted under OECD201 method. The toxic effect of CuO NP was investigated at 5 different concentrations of 2.5, 6.5, 17.4, 45.7, 120 mg/L against control in three replicates for each treatment and control. All samples were treated at constant temperature of 24 °C and 12-hour period of light and dark for 72 hours. Algae count was done at time intervals of 24, 48 and 72h. Chlorophyll assay was done according to ASTM standard. 

EC10, EC50, and EC90 amounts for 72 hours were 0.18, 28.84 and 4477.35 mg/L, respectively. With time, chlorophyll concentration was decreased in all treatments except for 57.68 mg/L. Carotenoid showed significant decrease between all treatments and the control and also among different treatments (p<0.05) and in 72h three treatments had different carotenoids (p<0.05).Discussion and

These results showed that CuO NP had significant toxic effect on Scenedesmus dimorphus and resulted to reduction in growth rate and increase in doubling time. Also, the percent inhibition was increased with increasing CuO NP concentration. The chlorophyll and carotenoid levels decreased in Scenedesmus dimorphus by increasing CuO NP concentration.

Cyanobacteria are regarded as good candidates for natural pruduct discovery, with applications in ‎pharmaceuticals industry. The majority of bioactive metabolites have either been polyketides, non-ribosomal ‎peptides, or a hybrid of the two. Despite of several worldwide studies on prevalence of NRPSs, none of them ‎included Iranian cyanobacteria of Lavasan Lake. Therefore, the aim of this study was to show that the presence of ‎these genes correlates with natural product synthesis. ‎

‎‏ ‏In this study, ten cultured fresh water cyanobacteria strains of the Lavasan Lake were ‎identified based on the sequence of 16SrRNA gene. In order to phylogenetic analysis the genes responsible for the ‎production of secondary metabolites, a NRPS PCR was conducted. Bioinformatics software tools were used in ‎order to prediction of peptide compound, amino acid activated and the signature sequences by a specific unknown ‎NRPS A module. Antibiogram bioassays were conducted to detect the presence of antimicrobial effects. Lastly, ‎studied strains have been deposited at the Cyanobacteria Culture Collection (CCC) of herbarium ALBORZ at the ‎Science and Research Branch, Islamic Azad University, Teheran.‎

the results showed that NRPS genes are presence in all strains. Morover bioinformatics analysis confirmed ‎the type of natural compound, signature sequences and predicted amino acid. In clusterimg of NRPS protein ‎sequences, there was no clear phylogenetic correlation between adenylation domains and activated amino acid and ‎this result emphasize the variety of adenylation domains. Morover the results of antibiogram bioassays showed ‎that there are positive correlation between the presents of those genes and antimicrobial activity.‎Discussion and

Sequence analysis indicates the enzymes encoded by these genes may be responsible ‎for the production of different secondary metabolites, such as antibiotics. The presented results prove that fresh ‎water cyanobacterial of Iran are a promising source to yield chemical and pharmaceutical interesting compounds.‎

Soil contamination by heavy metals, including lead, is one of the most important environmental hazards and a major factor in the ecological collapse. Bioremediation by resistant bacteria is one of the suitable methods for the removal of these heavy metals, which has other advantages, including environmental compatibility, low cost and stimulation of plant growth. The present study was conducted to isolate and identify lead-resistant rhizobacteria from long-term lead-contaminated soil based on morphological characteristics, biochemical tests and sequencing of 16SrRNA gene.

The rhizosphere samples were collected and diluted on the modified LB media.The colonies were studied based on morphological characteristics, biochemical tests, and ultimately molecular identification based on sequencing of the 16SrRNA gene.

Five isolates of lead-resistant Rhizobacteria were identified in this study. All strains showed the ability to tolerate high concentrations of lead (3.26 to 5.9 mM), moreover, all samples have the ability to produce indole acetic acid (88.87 to 38.58 mgl-1). Discussion and

Inoculation of hyperaccumulator plants with these lead tolerant rhizobacteria can be effective in improvement of the phytoremediation efficiency in lead contaminated soils.

Xanthan is an extracellular polysaccharide produced by Xanthomonas genus. Because of high viscosity and other properties, this gum is used in various industries. Hence, the use of cheap carbon sources such as whey can be economically feasible to produce Xanthan gum with positive lactose strains of Xanthomonas.

In this study, the native strain of Xanthmonas citri 386 was used to produce xanthan gum in cheese whey medium. The strain was cultured in a yeast extract lactose broth (YL) and then inoculated into production medium, the fermentation process was investigated in 5 days’ time in terms of production variables such as growth, consumption of lactose, viscosity and amount of xanthan. The content of pyruvate and acetate of product were compared with standard xanthan and the FTIR method was used to determine the functional groups.

The strain used was the ability to use lactose in cheese whey. At the end of the fermentation process, the amount and viscosity of xanthan were estimated to be 20.3 g/L and 2066.5 centipoise respectively. The acetate and pyruvate content was acceptable in comparison with standard xanthan, and the FTIR study confirmed the position of the functional groups of the xanthan structure.

In this study, for the first time, the native isolate of Xanthomonas citri 386 was evaluated for the production of xanthan in whey. This strain showed high potential for lactose consumption in whey and produced a significant amount of xanthan with an optimum viscosity. Therefore, at an industrial scale, the use of this native isolate, can be suitable for the production of xanthan by low-priced whey medium. Keywords: Xanthan gum, Xanthomonas citri, cheese whey, acetate and Pyruvate

Synthetic estrogen, 17α-ethinylestradiol (EE2), has adverse effects on aqueous environments even at the lowest concentrations. Identification of microorganisms with high degradation capability has always been expected. Biodegradation processes may involve the action of different microorganisms and microbial consortia, during which, either pollutants are consumed for growth or transformed due to co-metabolism. In this study, an enrichment culture of activated sludge from the pharmacy wastewater treatment unit was used for degradation of EE2 as the sole source of carbon and energy. For obtaining the strains with the capability of EE2 degradation, the sludge samples were used as seed and the enrichment culture was performed using mineral salt medium (MSM) with EE2 as the sole carbon source. To evaluate the EE2 degradability of the mixed culture, EE2 was added to the cultures at initial concentrations of 0-4 mg L-1. The degradation rate of EE2 (using HPLC) and the biomass concentration (using spectrophotometry) were monitored during the biodegradation process and the kinetic results were also investigated. Two colonies were obtained from the enrichment culture solution of activated sludge. It was concluded that the obtained mixed culture was able to degrade EE2 at different initial concentrations. Considering the probability of presence of multi-enzymes systems in the mixed culture which exhibit the property of cooperativity, the allosteric sigmoidal model was matched with the experimental data. The concentration of biomass was clearly increased along with EE2 biodegradation. The Monod growth equation was applied for modeling the variations of biomass concentration. Discussion and In this study a mixed culture capable of degrading EE2 as the sole carbon and energy source was isolated from the activated sludge of the pharmacy wastewater treatment unit. EE2 was used as a growth substrate due to the increase in the cell population.