Bioflocculant production by marine psychrotolerant Psychrobacter cibarius H41A KF207755 with its special role in silver nanoparticles production

The present study screened 23 previously isolated and identified marine psychrotolerant bacterial strains for the production of bioflocculant. Factors affecting the production process as well as the bioflocculant activity, in addition to the biosynthesis and the characterization of silver AgNPs were carried out. Psychrobacter cibarius H41 AKF207755 exhibited high bioflocculation activity at 75.3%. The effect of different physical and nutritional factors on the bioflocculant production process by P. cibarius H41Awas determined. The bioflocculating activity was increased to 82.1% after incubation for 60 h and to 84.7% at pH 6.5. Also, sucrose and urea improved the activity. The type of cations, pH level, and temperature were examined on the produced bioflocculant, which reached to 90.3% at pH 9 and to 92.1% at 70ºC. The addition of FeSO₄ raised the bioflocculant activity up to 94.0%. The concentrations of total protein, total carbohydrate, and total lipid were estimated for the partially purified bioflocculant as; 20.285, 31.215, and 12.2 gL^-1, respectively. It was found that the AgNPs can be synthesized using the bioflocculant, which remains stable for up to 16 months. Characterization of these AgNPs by UV-spectroscopy, FTIR, and TEM analyses takes place. The pH 11 supported the maximum synthesis of AgNPs at 2 mM AgNO₃. TEM revealed that the size of the produced AgNPs ranged from 1.31 nm to17.45 nm and no agglomeration was observed. Upon the applicable level, the antimicrobial property of AgNPs synthesized by the bioflocculant of P. cibarius H41A KF207755 was confirmed. The concentration dosage that gave the optimum flocculating activity (92.5%) was 4.0 mgmL^-1.