Characterization of an Exopolymeric Flocculant Produced by a Brachybacterium sp

We evaluated the bioflocculant production potential of an Actinobacteria, which was isolated from a freshwater environment in the Eastern Cape province of South Africa. 16S rDNA nucleotide sequencing analyses revealed that the actinobacteria belongs to the Brachybacterium genus, and the sequences were deposited in the GenBank as Brachybacterium sp. UFH, with accession number HQ537131. Optimum fermentation conditions for bioflocculant production by the bacteria include an initial medium pH of 7.2, incubation temperature of 30 °C, agitation speed of 160 rpm and an inoculum size of 2% (vol/vol) of cell density 3.0 × 10⁸ CFU/mL. The carbon, nitrogen and cation sources for optimum bioflocculant production were maltose (83% flocculating activity), urea (91.17% flocculating activity) and MgCl₂ (91.16% flocculating activity). Optimum bioflocculant production coincided with the logarithmic growth phase of the bacteria, and chemical analyses of the bioflocculant showed 39.4% carbohydrate and 43.7% protein (wt/wt). The mass ratio of neutral sugar, amino sugar and uronic acids was 1.3:0.7:2.2. Fourier transform infrared spectroscopy (FTIR) indicated the presence of carboxyl, hydroxyl and amino groups, amongst others, typical for heteropolysaccharide and glycosaminoglycan polysaccharides. Bioflocculant pyrolysis showed thermal stability at over 600 °C, while scanning electron microscope (SEM) imaging revealed a maze-like structure of interlaced flakes. Its high flocculation activity suggests its suitability for industrial applicability.