Production of Poly(3-hydroxybutyrate- co-3-hydroxyvalerate) (PHBV) by Haloferax mediterranei Using Candy Industry Waste as Raw Materials

Abstract

The haloarchaeon Haloferax mediterranei synthesizes poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) under unfavorable nutritional conditions without the addition of any precursor to the culture, which is an advantage compared to other microbial counterparts able to synthesize polyhydroxyalkanoates (PHA). PHBV is a biodegradable polymer showing physiochemical properties of biotechnological and biomedical interest and can be used as an alternative to plastics made from chemical synthesis (which are not environmentally friendly). The versatile metabolism of H. mediterranei makes the use of waste as a carbon source for cellular growth and PHA synthesis possible. In this work, cellular growth and the production and characterization of PHBV using two different types of confectionery waste were analyzed and compared with cellular growth and PHBV synthesis in a standard culture media with glucose of analytical grade as a carbon source. The PHBV granules produced were analyzed by TEM and the biopolymer was isolated and characterized by GC-MS, FTIR NMR, and DSC. The results reveal that H. mediterranei can use these two residues (R1 and R2) for pure PHBV production, achieving 0.256 and 0.983 g PHBV/L, respectively, which are among the highest yields so far described using for the first-time waste from the candy industry. Thus, a circular economy-based process has been designed to optimize the upscaling of PHBV production by using haloarchaea as cell factories and valorizing confectionery waste.

Keywords: bioplastics; candy waste; haloarchaea; poly(3-hydroxybutyrate) (PHB); poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV); poly(3-hydroxyvalerate) (PHV); polyhydroxyalkanoates (PHA).

Figure 1

Growth curve (OD₆₀₀) of H. mediterranei with the different carbon sources.

Figure 2

Electron micrographs of H. mediterranei cells grown with candy industry residues demonstrate the accumulation of PHA granules. Cells were harvested at the beginning of the stationary phase of growth.

Figure 3

Attenuated total reflectance–Fourier transform infrared (ATR–FTIR) spectra of the PHBV purified from H. mediterranei and of the commercial PHBV ENMAT Y1000P (3HV content ≈ 1 mol %).