title: Metabolomic characterization of halophilic bacterial isolates reveals strains synthesizing rare diaminoacids under salt stress.
abstract: Metabolomics-based approaches to study stress responses in bacteria have received much attention in recent years. In the present study, a metabolomic analysis of the representative halophilic bacterial isolates (Halomonas hydrothermalis VITP9, Bacillus aquimaris VITP4, Planococcus maritimus VITP21 and Virgibacillus dokdonensis VITP14) from a saltern region in India was performed using nuclear magnetic resonance spectroscopy. Chemometric analysis of (1)H NMR spectra revealed salt-dependent increase in the levels of metabolites, mainly from the aspartate and glutamate family, that are directed from the glycolytic pathway, pentose phosphate pathway and citric acid cycle. The composition of the metabolites was found to be different with respect to the species and the type of growth medium. Analysis of the two dimensional NMR data revealed accumulation of two rare diaminoacids, Nε-acetyl-α-lysine and Nδ-acetylornithine (by VITP21 and VITP4 strains respectively) apart from other well known solutes such as ectoine, proline, glutamate and glycine betaine. Metabolite profiles of strains capable of synthesizing Nε-acetyl-α-lysine and Nδ-acetylornithine suggested their biosynthesis from lysine and ornithine using aspartate and glutamate as their precursors, respectively. Further, the cells in moderate salinity (5% w/v NaCl) showed an increase in growth rate along with increase in the levels of nucleotides, whereas at higher salinity (10% w/v NaCl), the levels of aromatic and hydrophobic metabolites dropped, accompanied with a decrease in growth rate, rightly suggesting that at any salt-stress condition provided, cellular homeostasis was favored over growth.
authors.affiliation: School of Bio Sciences and Technology, Vellore Institute of Technology, Vellore 632 014, India.
authors.forename: Nidhya Nadarajan
authors.initials: NN
authors.lastname: Joghee
authors.affiliation: School of Bio Sciences and Technology, Vellore Institute of Technology, Vellore 632 014, India. Electronic address: gjayaraman@vit.ac.in.
authors.forename: Gurunathan
authors.initials: G
authors.lastname: Jayaraman
mesh_terms: D001105:Archaea / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D001224:Aspartic Acid / Q000737:chemistry; D003470:Culture Media; D016931:Halobacteriales / Q000187:drug effects / Q000378:metabolism; D008239:Lysine / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D055432:Metabolomics; D054712:Salinity; D012965:Sodium Chloride / Q000633:toxicity*
chemical_list: D003470:Culture Media; D001224:Aspartic Acid; D012965:Sodium Chloride; D008239:Lysine
keywords: Halophiles; Metabolomics; Nδ-Acetylornithine; Nε-Acetyl-α-lysine; Salt stress