Detection and quantification of poly(3-hydroxybutyrate) in cyanobacterial cell mass by Fourier transform infrared spectroscopy

The polymer poly(3-hydroxybutyrate) (PHB), a member of the polyhydroxyalkanoate (PHA) group, is naturally synthesised by cyanobacteria, and genetic engineering can increase its yield. These photoautotrophic organisms use CO 2 and light as carbon and energy sources, offering a sustainable approach to biobased, biodegradable polymers. In biotechnological PHB production, fast and accurate quantification of the polymer content is essential for up-scaling, process optimization, and quality control. Conventional methods such as chromatography require extensive sample preparation and hazardous solvents, limiting their applicability for rapid monitoring. This study introduces a fast, environmentally friendly, and unambiguous Fourier transform infrared (FT-IR) spectroscopy method for direct PHB quantification in crude cyanobacterial biomass. Three batches of dried cell mass from genetically modified Synechocystis sp. PCC 6803 and pure PHB were used to prepare blends with defined PHB contents. FT-IR spectra were processed using an automated procedure, and correlations between spectral key figures and PHB content were established. Among tested models, the exponential function using key figure peak ratio 1720 / 1640 achieved a high correlation ( R e x 2 = 0.941 ) and best validation compared to gas chromatography–mass spectrometry (GC-MS), with a maximum absolute deviation of only 2.10 wt%. The developed method eliminates time-consuming sample preparation and avoids hazardous chemicals, enabling rapid and reliable PHB quantification directly from biomass. This work serves as a basis for real-time monitoring of polymer accumulation, adaption for other PHAs, or direct quantification from liquid cultures, supporting scalable and sustainable bioprocess development.