https://doi.org/10.17113/ftb.60.03.22.7372

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Growth of Methylobacterium organophilum in Methanol for the Simultaneous Production of Single-Cell Protein and Metabolites of Interest

Ana Cristina Pantoja Simões^1*, Rodrigo Pimentel Fernandes¹, Maysa Silva Barreto², Gabriela Bouça Marques da Costa² Mateus Gomes de Godoy³, Denise Maria Guimarães Freire² and Nei Pereira Jr.¹

¹Laboratories of Bioprocess Development, School of Chemistry, Federal University of Rio de Janeiro, RJ 21941-972, Brazil

²Microbial Biotechnology Laboratory, Institute of Chemistry, Exact and Natural Sciences Center of the Federal University of Rio de Janeiro, RJ 21941-972, Brazil

³Laboratory of Biotechnology and Microbial Ecology, Institute of Microbiology, Federal University of Rio de Janeiro, RJ 21941-902, Brazil

Article history:

Received: 11 June 2021

Accepted: 9 April 2022

Key words:

single cell protein; methylotrophic bacterium; methanol consumption

Summary:

Research background. This study aims to monitor the growth of the methylotrophic bacteria Methylobacterium organophilum in a culture medium with methanol as a carbon source and to verify the production of unicellular proteins and other biomolecules, such as carotenoids, exopolysaccharides and polyhydroxyalkanoates, making them more attractive as animal feed.

Experimental approach. Bacterial growth was studied in shake flasks using different carbon/nitrogen (C:N) ratios to determine their best ratio for achieving the highest volumetric productivity of cells and substrate consumption rate. This optimal parameter was further used in a fed-batch operating bioreactor system to define the kinetic profile of cell growth. Methanol consumption was measured by HPLC analysis and the extracted pigments were analyzed by liquid chromatography/mass spectrometry. Chemical composition and rheological properties of the produced exopolysaccharides were also determined.

Results and conclusions. The best experimental parameters were verified using an initial methanol concentration of 7 g/L in the culture medium. The same initial substrate concentration was used in the fed-batch operation and after 60 h of cultivation 5 g/L of biomass were obtained. The accumulation of carotenoids associated with cell growth was monitored, reaching a concentration of 1.6 mg/L at the end of the process. These pigments were then analyzed and characterized as a set of xanthophylls (oxidized carotenoids). In addition, two other product types were identified during the fed-batch operation: exopolysaccharides, which reached a concentration of 8.9 g/L at the end of the cultivation, and an intracellular granular structure that was detected by transmission electron microscopy (TEM), suggesting the accumulation of polyhydroxyalkanoate (PHA), most likely polyhydroxybutyrate.

Novelty and scientific contribution. Methylobacterium organophilum demonstrated a unique ability to produce compounds of commercial interest. The distinct metabolic diversity of this bacterium makes room for its use in biorefineries.