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The present research aimed at evaluating the effects of urease enzyme and increasing pH on calcite nanocrystal formation. Unlike some researches, the results showed that CaCO3 precipitation is not a general phenomenon among the bacteria and if a bacterium has not this ability, it will not be able to produce calcite even with an increase in pH. All urease-positive bacteria had this ability, while only some urease-negative bacteria were able to produce calcite. Production and characterization of nanocrystals on precipitating medium were shown primarily by light microscopy and then confirmed by X-ray diffraction (XRD) analysis. Crystallite particle size was determined using Scherrer formula that was sub-100-nm in all samples. Based on qualitative and quantitative studies, strain C8 was selected as the best calcite-producing strain. Phylogenetic analysis indicated that this isolate has 99 % similarity with Enterobacter ludwigii. 16S rRNA sequence of isolate was deposited in GenBank with accession number JX666242. The morphology and exact composition of nanocrystalline particles were determined using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). According to data obtained by SEM, we suggest that nanocrystals of CaCO3 adhere to bacteria and each other to form small aggregates and then complex crystalline networks to trap bacteria. Many holes are present in these crystalline networks that seem to be due to the aggregation of nanocrystals.

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Aims: The aim of this research was production of polyphosphate (poly P) and study on its antibacterial effects. Methods and Results: Poly P granules in the cells were observed with the help of Albert staining and extracted by Mussig-Zufika method. Thin layer chromatography and nuclear magnetic resonance spectroscopy ( 31 P NMR) were used to characterize properties of these granules. Relation of phosphorus consumption and poly P production with growth was determined by the vanado-molybdate colorimetric method. Among the 60 strains of bacteria isolated from the environmental samples, strain G11 showed ability for the formation of high levels of poly P. Phylogenetic analysis showed that this isolate had 98% similarity with Bacillus megaterium. 16S rRNA sequence of isolate was deposited in GenBank with accession number JX115009. The average poly P chain length was 10Á5 in this bacterium. The antimicrobial activity of bacterial extracted poly P was much better than chemical poly P, and its interaction with gentamicin increased the activity of this drug. The best synergistic activity of this interaction was observed for Corynebacterium glutamicum and Pseudomonas aeruginosa species. The highest adsorption of phosphorus occurred in stationary phase of growth curve, and then the amount of phosphorus increased in medium by degradation of stored poly P. Conclusions: In this study, we isolated a high-level producer bacterium of poly P and extracted poly P by chemical treatment. In addition, we compared antimicrobial activity of chemical poly P with bacterial poly P and its interaction with gentamicin against both Gram-positive and Gram-negative bacteria. Significance and Impact of the Study: Many studies have shown that bacteria are becoming resistant to gentamicin sulphate. In this study, we approved that Acinetobacter baumannii, a pathogenic gentamicin-resistant bacterium, is sensitive to bacterial poly P, and thus, this poly P can be substituted for gentamicin in treatment.