فصلنامه زیست شناسی میکروارگانیسم ها
پیاپی 24 (زمستان 1396)

Siderophores are relatively low-weight molecules (500 to 1000 Dalton), which are produced by many microorganisms as the chelating ligands of iron under iron deficiency. Plants can absorb the siderophore-iron complex to meet their needs for iron. The aim of this study was isolation and identification of siderophore producing bacteria.
In this study, we used liquid chrome azurol S (CAS) assay for the isolation of siderophore producing plant growth promoting rhizobacteria (PGPRs). Then, different kinds of the produced siderophores by the best strains were determined using overlaid chrome azurol S (O-CAS) assay. Finally, two best siderophores producing strains were identified using the 16S rDNA gene sequencing analysis.
The results showed that 69.3 percent of the isolated bacteria could produce siderophores. The lowest and highst levels of siderophores belonged to the strains Cke1 (17.58 percent siderophore unit) and Wah1 (97.76 percent siderophore unit) respectively. Based on the O-CAS assay method, these strains produced catchol and hydroxamat types of siderophores. Two strains Wah1 and Wkh were identified using 16S rDNA gene sequencing analysis as Bacillus cereus and Enterobacter cloacae, respectively.
Discussion and Wah1 and Wkh produced more siderophores (as siderophore unit) than other strains, which were studied using the same method until now. Therefore, they could be valuable strains to study their potential as biological fertilizers and plant protection against the soil born pathogens.

Microbial biopolymers such as polyhydroxyalkanoates (PHA) are proper alternatives for petroleum-derived plastics. These biopolymers have many advantages over conventional plastics such as biodegradability, environmental friendly and infinite as a renewable resource. Therefore, our study was aimed to isolate a bacterial strain capable of producing polyhydroxybutyrate (PHB; a highly applicable type of PHA).
To this aim, a total of 6 PHA-producing bacteria were isolated from waste water exit site of a brewery factory. The 6 isolates were studied by Sudan black-staining technique and the most stained isolate was selected for further studies. Next, the selected isolate was identified based on morphological, biochemical and phylogenetic analyses. Finally, the ability of strain in producing PHB as well as other PHAs was analyzed via GC-MS technique.
Strain NG had the highest yield of PHB, according to Sudan black-staining technique and it was selected for further studies. The strain NG was identified as a new strain of Bacillus thuringiensis. According to GC-MS results, this strain was able to produce PHB as well as 4 other PHAs including hexadecanoic acid methyl ester, octadecanoic acid methyl ester, tetradecanoic acid methyl ester, 8-octadecenoic acid methyl ester.
Discussion and It was the first report on producing various PHAs at the same time by a strain of Bacillus thuringiensis.

The present study was carried out to evaluate the occurrence of toxicogenic Fusarium proliferatumstrains isolated from nuts in Iraq.
A total of 108 nut samples collected from different markets in Iraq. Strains of Fusarium spp. isolated from nuts seeds and their morphological characterization of the strains were examined based on their growth on carnation leaf agar (CLA) and potato dextrose agar (PDA). The identification of F. proliferatum isolates were confirmed molecularly using species specific primers of PRO1/PRO2 primers. PCR-based detection of fumonisin-synthesis-pathway gene was also used to determine the potential of F. proliferatum isolates to produce fumonisin using FUM1 gene-based (FUM1 F/FUM1 R) primers.
Based on morphological features 28 fungal isolates were obtained from nuts and identified into four species F. proliferatum (12), Aspergillus niger (8), Aspergillus flavus (5), and Penicillium sp. (3). The primers PRO1/PRO2 produced DNA fragments 585 bp in all F. proliferatum strains. PCR assays also showed DNA fragments (183 bp) were amplified in nearly 42% of F. proliferatum strains.
Discussion and Of 12 tested isolates, 5 isolates (~42%) being fumonisin chemotype. To our knowledge, this is the first report on molecular identification and mycotoxigenic capacity of Fusarium fujikuroi species complex (FFSC) isolated from nuts in Iraq.

The Rhizobium-legume interaction leads to biological nitrogen-fixation and increases nitrogen of soil. The aim of this study was to characterize the properties of Sinorhizobium isolates from the roots of alfalfa plantsin Iran.
Bacteria were isolated in yeast extract mannitol Agar and confirmed by plant infection test. After evaluation from the point of morphological and biochemical properties, a fragment of 16S rDNA gene with a size of approximately 1500 base pair was amplified using fD1 and rD1 primers. PCR (polymerase chain reaction) products were analyzed for digestion pattern by Taq1 endonuclease.
63 bacteria were isolated from homogenized nodules. 42 isolates generated nodules in three replicates in infection test. Of the 42 isolates 8, were resistant to salinity. Seven isolates had better growth than others at pH 4. All isolates were resistant to CuCl2 (0.5 mmol), CdCl2 (0.65 mmol), MnSO4 (0.75 and 1.5 mmol) and ZnSO4 (0.125 mmol). Isolates S3Q and S22K were more resistant to salinity, acidity, temperature and heavy metals stresses. PCR products of all bacteria had the same restricted profile after digestion by Taq1 nuclease.
Discussion and The results showed that among isolated bacteria, there were some differences in the resistance to salinity, acidity, temperature and heavy metals stresses. Identification of native strains of rhizobia, especially strains resistant to salinity, temperature, heavy metals and acidity could be valuable due to their potentiality for using biological fertilizers in harsh conditions.

Phytopathogenic microorganisms affect plant health and burden a major threat to food production and ecosystem stability. Increasing the use of chemical pesticides for plant diseases control causes several negative effects on human and environment health. Furthermore, increasing public awareness about the side effects of them led to a research to find alternatives for these products. One of the alternative methods is bio-control utilizing plant associated antagonistic microorganisms.
In this study, 80 endophytic bacteria were isolated from tomato tissues. Their antagonistic activity screened based on agar diffusion test, against tomato bacterial wilt disease (Ralstonia solanacearum). They were identified based on the morphological, biochemical properties and 16s rRNA sequence analyses. These strains were evaluated in greenhouse and tested for their ability to induce the production of defense-related enzymes in plants e.g. Peroxidase (PO), polyphenoloxidase (PPO) and phenolics based on spectrophotometer method.
Results showed FS67, FS167 and FS184 strains had maximum inhibition zone forming. They identified as Pseudomonas mossellii, P. fuorescence and P. brassicacearum respectively. FS67 and FS167 strains significantly reduced disease in greenhouse. There was a significant increase in the activity of PO, PPO and phenolics in tomato plants treated with FS67, FS167 and pathogen.
Discussion and The present study has shown that P. mosselli and P. fuorescence might have the potential to control R. solanacearum. However, the good results obtained in vitro cannot be gained the same as those in greenhouse or field conditions. So, further experiments are needed to determine the effectiveness of these isolates under field conditions.This work support the view that increased defense enzymes activities could be involved, at least in part, in the beneficial effects of endophytic bacteria on plants growth in interaction of pathogens. This is the first report of antagonistic activity of Pseudomonas mossellii from Iran.

Phytase hydrolyzes phytic acid and enhances bioavailability of phosphorus and other nutritive minerals for monogastric animals, so it is commonly used as an important food additive.
The aim of this study was isolation of phytase producing bacteria from one of Shushtar's bean farms, Southwest of Iran by phytase screening medium (PSM) and optimization of the growth and enzyme productive conditions by the best isolate.
The best isolate was identified as Citrobacter farmeri strain phas32. Optimized conditions for phytase production by this isolate were 30˚C, pH 7, 0.25% phytic acid and 48 h incubation and phytase enzyme of phas32 had the best activity at 65˚C and pH 8.5. Enzyme unit and its molecular weight were 31 U/ml and 40 KD, respectively.
Discussion and Finally, based on these results it can be concluded that the Citrobacter farmeri strain phas32 is potent phytase producer that can be used for large scale enzyme production.