Abstract
The biofloculant production potential of a consortium of Streptomyces and Brachybacterium species were evaluated. Optimum bioflocculant yields (g/L) and flocculation activities (%) were observed for the following preferred nutritional sources: glucose (56%; 2.78 ± 0.15 g/L), (NH4)2NO3 (53%; 2.81 ± 0.37 g/L) and CaSO4·H2O (47%; 2.19 ± 0.13 g/L). A Plackett-Burman design revealed the critical fermentation media components. The concentrations of these components were optimized [glucose; 16.0, (NH4)2NO3; 0.5 and CaSO4·H2O; 1.2 (g/L)] through a central composite design with optimum bioflocculant yield of 3.02 g/L and flocculation activity of 63.7%. The regression coefficient (R2 = 0.6569) indicates a weak estimation of the model’s adequacy and a high lack-of-fit value (34.1%). Lack of synergy in the consortium may have been responsible for the model inadequacy observed. FTIR spectrometry showed the bioflocculant to be a heteropolysaccharide, while SEM imaging revealed an amorphous loosely arranged fluffy structure with interstial spacing of less than 1 µm.
Highlights
Biopolymeric materials, of extracellular or intracellular origin, synthesized by some species of bacteria, fungi and algae have been variously documented to mediate flocculation of suspended particles in liquid media [1,2,3,4]
Besides bio-prospecting for novel bioflocculant-producing bacteria, strategies employed for yield optimization of microbial products include mutational analysis and manipulation of nutritional and fermentation conditions [19]
The different carbon, nitrogen and cation sources evaluated for optimal utilization for bioflocculant production showed Streptomyces sp. and Brachybacterium sp. consortium to optimally utilize glucose, (NH4)2NO3 and CaSO4·H2O respectively (Table 1)
Summary
Biopolymeric materials, of extracellular or intracellular origin, synthesized by some species of bacteria, fungi and algae have been variously documented to mediate flocculation of suspended particles in liquid media [1,2,3,4]. The growing interest in these biopolymers can be attributed to the advantages they possess over the conventionally used flocculants which include aluminum salts (aluminum sulphate and polyaluminum chloride), derivatives of polyacrylamide and polyethylene imines [5]. Appreciable flocculation activities has been reported for bioflocculants produced by several prokaryotes, fungi and a few algae [12,13,14] the high cost of bioflocculant production and low yield has been a major limiting factor to the industrial applications of these biopolymers [15,16,17]. Besides bio-prospecting for novel bioflocculant-producing bacteria, strategies employed for yield optimization of microbial products include mutational analysis and manipulation of nutritional and fermentation conditions [19].
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