فصلنامه زیست شناسی میکروارگانیسم ها
پیاپی 36 (زمستان 1399)

Some of plant growth-promoting rhizobacteria are endophytic bacteria that exist in the endo-rhizosphere and are able to promote plant growth via different mechanisms.

24 endophytic bacteria were isolated from the roots of grasses such as rice, wheat and barley using semi-solid nitrogen-free bromothymol blue (NFB) medium. PGP features including phosphate solubilization, indole acetic acid (IAA) production, potassium releasing and siderophore production were measured according to the standard methods.

The dissolution of phosphate 1.67 times was higher in the presence of tri-calcium phosphate (TCP) than rock phosphate (RP), and K release from biotite was more than muscovite (4.7 times); furthermore more IAA was produced in the presence of tryptophan, and this increment was by 30%. The highest and lowest amount of IAA were recorded in Az-3 (2.28 mg/l) and Az-48 (0.75 mg/l), respectively; while the maximum dissolution of phosphate obtained with Az-52 (340.13 mg/l) and the least dissolution of phosphate occurred in Az-13 (98.13 mg/l). The highest K release was accomplished by Az-65 (6.66 mg/l) and the lowest was in Az-3 (4.78 mg/l). Finally, identification of robust isolates by 16S rDNA sequencing showed that Az-8, Az-19, and Az-50 are belonging to the Pseudomonas, Az-3 to Acinetobacter, Az-18 to Rhizobium, Az-48 to Enterobacter, and Az-63 to Advenella. Discussion and

Our results revealed that different genera of bacteria with varied PGP traits are existing as endophytic bacteria in the plant roots. In total, these bacteria were able to solubilize more phosphate from TCP than RP; and higher K from biotite than muscovite. It seems that the production of organic acids is the main mechanism of P and K solubilization. Moreover, higher production of IAA was measured in the presence of tryptophan. Further research, especially in pot or farm, is necessary to assess the effects of these bacteria.

Shiga Toxin-producing Escherichia coli (STEC) is an important organism known as an emerging zoonotic microorganism causing diseases such as hemorrhagic colitis and Hemolytic Uremic Syndrome (HUS) as well as thrombotic thrombocytopenia in humans. This study aimed to determine the contamination of meat-contact surfaces to STEC and the characterization of the virulence genes of the isolates.

Totally, 111 swab samples were obtained from meat-contact surfaces in slaughterhouses and meat supply centers for 6 months. After the primary enrichment and cultivation on EMB and SMAC environments, sorbitol negative colonies were transferred to differential media and confirmed by specific tests as Escherichia coli. Suspected colonies were evaluated by PCR method to determine the existence of serotype O157: H7and virulence genes such as Stx1, Stx2, eae, and Hly.

E. coli O157 was detected in 14 samples (12.61%), and only 2 isolates (1.8%) were identified as E.coli O157: H7. In PCR, 4 isolates contained Stx1, Stx2, and Hly genes, 2 isolates contained Stx1, eae and Hly genes, 3 isolates contained Stx1 and Hly genes, 1 isolate contained Stx2 and eae genes, 3 isolates contained the Hly gene and 1 isolate did not have any of the virulence genes. Discussion and

Concerning the possibility of the transmission of pathogens such as E.coli O157: H7from contaminated surfaces to carcasses and healthy meat, the lack of attention to the health and care of slaughterhouses and meat supply centers can be concerns for the public health.

Propolis is one of the most important bee byproducts that, due to its high antimicrobial properties, has the potential to be used as a food additive. This study investigated the effects of aqueous and ethanolic extracts of propolis on the microbial load of raw milk.

Raw milk samples containing0.1, 0.5, 1, and 2% ethanolic extracts and 0.5, 1, 3, and 5% aqueous extracts were prepared. The treatments were incubated at 4 °C and 25 °C and were cultivated by pour-plate technique in PCA medium during storage times of 0, 2, 24, 48, and 72 hours. By a total count of microorganisms, the effects of different concentrations of propolis extracts on the microbial load of raw milk were investigated. The chemical compounds of the extracts were identified by gas chromatography–mass spectroscopy (GC-MS) analysis.

At 25 °C, all concentrations of aqueous and ethanolic extracts affected the microbial load of raw milk, but at low concentrations, such effects were observed after 24 hours. Aqueous and ethanolic extracts of propolis at 25 °C compared to 4 °C in lower concentrations showed more antimicrobial activity. It was also found that propolisextracts need time to exhibit high antimicrobial activity. Forty-onecompounds were identified with the dominance of phenolic and flavonoid compounds. Discussion and

The antimicrobial properties of the tested propolis extracts can be attributed to the high amounts of phenolic and flavonoid compounds and the use of this bee product as an additive is recommended.

Vitamin B12 is a key factor in many growth-related processes in the human body and its large-scale industrial production is carried out using microorganisms, especially Propionibacterium freudenreichii. The aim of this study was to evaluate the effect of folic acid, methionine, and oxygen on the optimal production of vitamin B12 and Dry Cell Weight (DCW) of this bacterium.

Bacteria were maintained in four different conditions including anaerobic conditions and different concentrations of folic acid, aerobic conditions and different concentrations of folic acid, anaerobic conditions and different concentrations of folic acid and methionine 0.05% (w/v), aerobic conditions and different concentrations of folic acid and methionine 0.05% (w/v).

The maximum production of vitamin B12 and DCW was obtained in 750 mg / L of folic acid in the presence of methionine and aerobic conditions. By increasing the concentration of folic acid up to 1000 mg / L, the amount of vitamin B12 production and dry weight of the bacterium decreased. Discussion and

Due to the effect of folic acid on the fermentative processes of Propionibacterium freudenreichii, the present study could be an effective optimization to increase the final production of vitamin B12. Based on the above findings, aerobic conditions along with the presence of methionine can be effective in improving vitamin B12 production and this optimization may help as an effective strategy to improve vitamin B12 production at the industrial level.

Bacteria in cold ecosystems play a vital role in biochemical cycles, the biodegradation of pollutants, and biotechnology. For this reason, the identification and evaluation of their extracellular enzymes have received a lot of attention in recent years.

In this study, 43 psychrophilic or psychrotolerant bacteria were characterized from alpine soils on different culture media. The ability to produce extracellular enzymes by these bacteria was studied.

These bacteria belonged to the four major phyla including Actinobacteria, Firmicutes, Proteobacteria, and Bacteroidetes.A total of nine genera were identified among which Pseudomonas, Arthrobacter, and Bacillus were the most abundant.
Discussion and

All of the obtained strains have the ability to produce at least one extracellular enzyme; proteolytic and amylolytic activities were the highest among these strains. Cellulase and pectinase activities were observed in 44 and 22 percentage of these strains. This study was the first report on psychrophilic and psychrotolerant bacteria in the Zagros Mountains (Oshtorankuh) and their extracellular enzyme production. The present study indicated that a wide range of bacteria in cold native ecosystems of Iran can be a suitable source for cold active enzymes.