Isolation, characterization, optimization, immobilization and batch fermentation of bioflocculant produced by Bacillus aryabhattai strain PSK1

Among others, isolate PSK1 was selected and identified by 16 S rDNA sequencing as Bacillus aryabhattai. Growth optimization of PSK1 and physicochemical parameters affected bioflocculant production was carried out by Plackett-Burman design and resulted in increasing in the activity by 4.5%. Bioflocculant production by entrapped and adsorbed immobilized microbial cells was performed using different techniques and revealed enhancement in the activity in particular with pumice adsorption. HPLC analysis of sugars and amino acids composition, FTIR and the effect of different factors on the purified PSK1 biopolymer such as presence of cations, thermal stability, pH range and clay concentration was carried out. Scanning electron microscopy (SEM) of free, immobilized cells, PSK1 bioflocculant and formed flocs were performed. The results revealed that bioflocculant PSK1 is mainly glycoprotein consists of glucose and rhamnose with a large number of amino acids in which arginine and phenylalanine were the major. SEM analysis demonstrated that PSK1 have a clear crystalline rod shaped structure. FTIR spectrum reported the presence of hydroxyl and amino groups which are preferred in flocculation process. PSK1 was soluble in water and insoluble in all other tested organic solvents, while it was thermally stable from 40 to 80 °C. Among examined cations, CaCl2 was the best coagulant. The maximum flocculation activity of the PSK1 recorded at 50 °C (92.8%), pH 2.0 (94.56%) with clay concentration range 5-9 g/l. To obtain a large amount of PSK1 bioflocculant with high flocculating activity, batch fermentation was employed. The results recorded ∼6 g/l yield after 24 h of fermentation.