Effects of Various Stress Conditions to Enhance Polyhydroxyalkanoates Accumulation in Wickerhamomyces anomalus VIT-NN01

Abstract

Polyhydroxyalkanoates (PHA) are polyesters produced by various microorganisms. The major drawback of PHA, which is restricting its large-scale production in industries, is its high cost of raw materials and lower PHA concentration. The present study aimed to enhance the production of PHA from Wickerhamomyces anomalus VIT-NN01 by optimizing various nutrient and environmental stress conditions and its characterization. Effect of various stress conditions viz. nitrogen limitation, salinity, chemical mutagens (acridine orange, sodium azide), and physical stresses (UV, Low Electric Current (LEC), Magnetic Field Intensity (MFI), sound waves) were optimized to screen the best strategic growth conditions for the maximum accumulation of PHA in W. anomalus VIT-NN01. Instrumental analysis was done to evaluate the various changes that occurred in the treated cells and extracted PHA. The maximum PHA content was observed on the effect of sound waves (88.74%), followed by LEC (87.8%) and MFI (85.75%). The morphological changes in length, shape, and size of the treated W. anomalus cells were observed by Transmission Electron Microscopy (TEM). Smooth, porous matrix, and pseudo spherical microstructure of the extracted PHA were observed by scanning electron microscopy and TEM analysis. The extracted polymer was identified as poly(3-hydroxybutyrate-co-3- hydroxyvalerate) [P(3HB-co-3HV)] co-polymer comprised of 51.66% 3HB and 48.33% 3HV monomer units based on gas chromatography-mass spectrophotometer and nuclear magnetic resonance spectroscopic analysis. X-ray diffraction analysis revealed the crystalline nature of the extracted P(3HB-co- 3HV). The degradation and melting temperatures were found to be 275.9 and 113.8°C, respectively, through thermogravimetric and differential scanning calorimetry analysis. These results supported the potentiality of W. anomalus, which tolerated the stress conditions and enhanced P(3HB-co-3HV) production from 60 to 88.74% and showed the novelty of present work. This is the first report elucidating the importance of physical stress conditions viz. low electric current, magnetic field intensity, and sound waves for the significant enhancement of PHA production in yeast.