Genes encoding the production of extracellular polysaccharide bioflocculant are clustered on a 30-kb DNA segment in Bacillus licheniformis

Abstract

Bioflocculants are special high-molecular weight polymers produced by microorganisms. Despite the fact that several types of bioflocculants from different species of bacteria have been reported, there is a large gap in our knowledge regarding the molecular machine responsible for the production of bioflocculants. To investigate genes involved in bioflocculant synthesis, a fosmid library was generated from Bacillus licheniformis genomic DNA and screened for the production of bioflocculant. Four positive clones with distinct flocculation were isolated by a two-pooling scheme. The clone with 662 U ml(-1) flocculating activity was sequenced. As a result, a 30-kb fragment with 26 hypothetical genes was identified in the bioflocculant-producing clone. Most of the predicted proteins encoded by the inserted genes showed significant homology with enzymes involved in the biosynthesis of polysaccharide. Based on these homologies, a biosynthesis pathway and two gene clusters involved in the production of the polysaccharide bioflocculant were proposed with the integration of functional descriptions of individual genes by metabolic databases, and a glucose-sensitive glycosidases was predicted. This research supplied significant data for potential application of bioflocculant-producing strains in wastewater refining and industrial downstream treatments.

Poly-γ-glutamic acid produced fromBacillus licheniformisCGMCC 2876 as a potential substitute for polyacrylamide in the sugarcane industry

“…15 Similarly, the flocculation properties of g-PGA (6.2 3 10 6 Da) derived from B. subtilis R 23 indicated that g-PGA can be used in wastewater treatment plants and downstream processing of food and fermentation industries. 12 In this study, B. licheniformis CGMCC 2876, a strain that was previously identified to synthesize a polysaccharide bioflocculant in our laboratory, 16,17 was found to produce g-PGA with even higher FA. The effects of nutrients and chemical compositions on the production and flocculation activity of the g-PGA from B. licheniformis CGMCC 2876 were focused, and the flocculating efficiency of g-PGA was compared with commonly used chemically synthesized flocculant (PAM) in the sugar refinery process.…”

“…In this study, B. licheniformis CGMCC 2876, a strain that was previously identified to synthesize a polysaccharide bioflocculant in our laboratory, was found to produce γ‐PGA with even higher FA. The effects of nutrients and chemical compositions on the production and flocculation activity of the γ‐PGA from B. licheniformis CGMCC 2876 were focused, and the flocculating efficiency of γ‐PGA was compared with commonly used chemically synthesized flocculant (PAM) in the sugar refinery process.…”

Implications for public health demands alternatives to inorganic and synthetic flocculants: bioflocculants as important candidates

“…; Yan et al. ). The gene products, mostly enzymes, are involved in the formation of polysaccharides by sequential addition of sugars to membrane anchored repeating units which are then exported (Cerning ).…”

Characterization of a beta-glucosidase from Bacillus licheniformis and its effect on bioflocculant degradation

“…In the latter phase of polysaccharide fermentation, the flocculating activity decreases because of the degradation of this bioflocculant. At the same time, a gene encoding β-glucosidase (Bgl.bli1) in a bioflocculant-producing clone was predicted to be involved in polysaccharide bioflocculant dissimilation (Yan et al 2013). The present study describes the cloning, heterologous expression and biochemical characterization of this β-glucosidase.…”