Metabolic characterisation of <i>Magnetospirillum gryphiswaldense</i> MSR-1 using LC-MS-based metabolite profiling

Abstract

Magnetosomes are nano-sized magnetic nanoparticles with exquisite properties that can be used in a wide range of healthcare and biotechnological applications. They are biosynthesised by magnetotactic bacteria (MTB), such as <i>Magnetospirillum gryphiswaldense</i> MSR-1 (<i>Mgryph</i>). However, magnetosome bioprocessing yields low quantities compared to chemical synthesis of magnetic nanoparticles. Therefore, an understanding of the intracellular metabolites and metabolic networks related to <i>Mgryph</i> growth and magnetosome formation are vital to unlock the potential of this organism to develop improved bioprocesses. In this work, we investigated the metabolism of <i>Mgryph</i> using untargeted metabolomics. Liquid chromatography-mass spectrometry (LC-MS) was performed to profile spent medium samples of <i>Mgryph</i> cells grown under O₂-limited (<i>n</i> = 6) and O₂-rich conditions (<i>n</i> = 6) corresponding to magnetosome- and non-magnetosome producing cells, respectively. Multivariate, univariate and pathway enrichment analyses were conducted to identify significantly altered metabolites and pathways. Rigorous metabolite identification was carried out using authentic standards, the <i>Mgryph</i>-specific metabolite database and MS/MS mzCloud database. PCA and OPLS-DA showed clear separation and clustering of sample groups with cross-validation values of R²X = 0.76, R²Y = 0.99 and Q² = 0.98 in OPLS-DA. As a result, 50 metabolites linked to 45 metabolic pathways were found to be significantly altered in the tested conditions, including: glycine, serine and threonine; butanoate; alanine, aspartate and glutamate metabolism; aminoacyl-tRNA biosynthesis and; pyruvate and citric acid cycle (TCA) metabolisms. Our findings demonstrate the potential of LC-MS to characterise key metabolites in <i>Mgryph</i> and will contribute to further understanding the metabolic mechanisms that affect <i>Mgryph</i> growth and magnetosome formation.