title: Raman spectroscopic analysis of Lactobacillus rhamnosus GG in response to dehydration reveals DNA conformation changes.
abstract: Dehydration of bacterial cells elicits cellular stress responses in bacteria. Microencapsulation has been used to protect cells against the environmental stress. In this study, Confocal Raman Spectroscopy was used to examine DNA changes in the chemical composition of non-encapsulated and microencapsulated Lactobacillus rhamnosus GG and the reversibility of these changes upon freeze drying and rehydration. The viability of cells upon freeze drying was also enumerated using culture methods and membrane integrity was measured using BacLight Live/Dead staining. Raman analyses show changes in the spectral features associated with various biochemical compounds, which are interpreted as the result of detrimental freeze drying effects on the bacterial cells. Specifically, analyses based on Principal Components Analysis (PCA) of Raman spectra, confirm that microencapsulation protects cells from environmental stress. The results also reveal a B- to A-like DNA conformation change in dormant cells that provided insights into the extent of reversibility of this transition upon rehydration. The extent of this reversibility is less in non-encapsulated than in microencapsulated cells. These findings indicate the potential application of Raman spectroscopy in rapid sensing of microbial dehydration stress responses.
authors.affiliation: CSIRO Food and Nutrition, 671 Sneydes Road, Werribee, Victoria, 3030, Australia.
authors.forename: Mya
authors.initials: M
authors.lastname: Myintzu Hlaing
authors.affiliation: Centre for Biospectroscopy, School of Chemistry, Monash University, Victoria, 3800, Australia.
authors.forename: Bayden
authors.initials: B
authors.lastname: Wood
authors.affiliation: Centre for Biospectroscopy, School of Chemistry, Monash University, Victoria, 3800, Australia.
authors.forename: Don
authors.initials: D
authors.lastname: McNaughton
authors.affiliation: CSIRO Food and Nutrition, 671 Sneydes Road, Werribee, Victoria, 3030, Australia.
authors.forename: DanYan
authors.initials: D
authors.lastname: Ying
authors.affiliation: CSIRO Food and Nutrition, 671 Sneydes Road, Werribee, Victoria, 3030, Australia.
authors.forename: Mary Ann
authors.initials: MA
authors.lastname: Augustin
mesh_terms: D004269:DNA, Bacterial / Q000737:chemistry*; D003681:Dehydration; D004926:Escherichia coli; D005612:Freeze Drying; D052201:Lacticaseibacillus rhamnosus / Q000737:chemistry*; D050296:Microbial Viability; D009690:Nucleic Acid Conformation; D025341:Principal Component Analysis; D012815:Signal Processing, Computer-Assisted; D013059:Spectrum Analysis, Raman; D013312:Stress, Physiological; D014867:Water / Q000737:chemistry
chemical_list: D004269:DNA, Bacterial; D014867:Water
keywords: Raman spectroscopy; freeze drying; microencapsulation; probiotics