A rapid method for detecting bacterial polyhydroxyalkanoates in intact cells by Fourier transform infrared spectroscopy

Abstract

Polyhydroxyalkanoates (PHA) are synthesized by many bacteria as inclusion bodies, and their biodegradability and structural diversity have been studied with a view to their potential application as biodegradable materials. In this paper, Fourier-transform infrared spectroscopy (FT-IR) was used to carry out rapid qualitative analysis of PHA in intact bacterial cells. The FT-IR spectra of pure PHA containing short-chain-length monomers, such as hydroxybutyrate (HB), medium-chain-length hydroxyalkanoate (mclHA) monomers including hydroxyoctanoate (HO) and hydroxydecanoate (HD), or both HB and mclHA monomers, showed their strong characteristic band at 1728 cm−1, 1740 cm−1 or 1732 cm−1 respectively. Other accompanying bands near 1280 cm−1 and 1165 cm−1 helped identify the types of PHA. The intensity of the methylene band near 2925 cm−1 provided additional information for PHA characterization. In comparison, bacterial cells accumulating the above PHA also showed strong marker bands at 1732 cm−1, 1744 cm−1 or 1739 cm−1, corresponding to intracellular PHB, mclPHA and P(HB + mclHA) respectively. The accompanying bands visible in pure PHA were also observable in the intact cells. The FT-IR results were further confirmed by gas chromatography analysis.