Alkali-Tolerant Bacillus Producing PHA and Application of its PHA Surface Binding Protein as Surfactant

Abstract

Abstract Polyhydroxyalkanoates (PHA) produced by Bacillus bacteria have potential advantages in medical applications, due to its cell membrane do not contain outer membrane lipopolysaccharide (LPS). However, the PHA accumulation level is far lower than that of Gram-negative bacteria. In this study, an alkali-tolerant Bacillus cereus HBL-AI was screened using Nile Red and Sudan Black B in a Low-Salt LB solid medium at pH 8.0. This strain displayed high PHA accumulation capacity in fed‑batch fermentation with glucose as the carbon source in a 5 L unsterilized fermentor. The highest PHA accumulation reached 12.8 g/L and the extracted product was finally determined as (Poly-β-3-hydroxybutyrate, PHB). It has the potential to be used for large-scale open and continuous fermentation. Furthermore, PHA membrane binding protein (PhaP), PHA regulatory protein (PhaQ and PhaR) derived from HBL-AI were heterologously expressed inE. coli and purified to investigate their application as biosurfactants. The results showed that the emulsification ability and stability of three amphiphilic proteins were higher than those of widely used chemical surfactants. The protein concentration of PhaQ used to form a stable emulsion layer in vegetable oil was the lowest (50 μg/mL), which greatly reduced the amount of protein used in emulsification. This clearly demonstrated that HBL-AI has great potential in the production of PHA without endotoxin, and its PHA binding protein can be well applied as an environmentally friendly biosurfactants.