Production and characterization of a novel bioflocculant from Bacillus licheniformis

Abstract

A bacterium producing an extracellular bioflocculant was isolated from contaminated LB medium and identified as Bacillus licheniformis by 16S rRNA gene sequencing and its biochemical/physiological characteristics. The optimum culture conditions for flocculant production were an initial medium pH of 7.2 and an inoculum size of 4% (vol/vol). The maximum flocculating activity (700 U/ml) was obtained after cultivation at 37 degrees C for 48 h. Chemical analyses of the purified bioflocculant revealed that it was a proteoglycan composed of 89% carbohydrate and 11% protein (wt/wt). The mass ratio of neutral sugar, amino sugar, and uronic acid was measured at 7.9:4:1. Infrared spectrometry further indicated the presence of carboxyl, hydroxyl, and amino groups, typical of heteropolysaccharide. The average mass of the bioflocculant was calculated to be 1.76 x 10(6) Da. Scanning electron microscopy (SEM) images of the bioflocculant showed an irregular structure with netted texture. Its efficient flocculation capabilities suggest potential applications in industry.

FIG. 1.

Phylogenetic tree based on the nucleotide sequences of the 16S rRNA gene.

FIG. 2.

Time courses of the growth, pH, and flocculating activity of culture broth of B. licheniformis cultivated on a rotary shaker at 200 rpm and 37°C for 130 h.

FIG. 3.

Effect of initial pH on flocculant production by B. licheniformis CGMCC 2876.

FIG. 4.

Infrared spectra of purified bioflocculant from B. licheniformis CGMCC 2876.