Growth of Methylobacterium organophilum in Methanol Aiming at the Simultaneous Production of Single-Cell Protein and Metabolites of Interest
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
Received: 11 June 2021
Accepted: 9 April 2022
single-cell protein; methylotrophic; methanol
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 a compound more attractive as food intended for animal feed.
Experimental approach. Microbial growth was studied in shaken flasks to evaluate bacterial growth with different carbon/nitrogen ratios (C:N) and determine the best results in terms of cell volumetric productivity and substrate consumption rate. This condition was to be further applied in an in a fed-batch operating bioreactor system, which depicted the kinetic profile of cell growth, which concentrations were determined by dry cell weight, methanol consumption, measured by HPLC analysis, accumulation of carotenoids, which was analyzed by mass spectrometry, and the production of exopolysaccharide, which was characterized in terms of its chemical composition and submitted to chemical rheological analysis.
Results and conclusions. The best experimental condition was verified using an initial methanol concentration of 7 g/L in the culture medium. This same initial substrate concentration was used in the bioreactor in the fed-batch operation, and the biomass concentration was 5 g/L, after 60 hours of cultivation. 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 products were identified during the fed-batch operation: an exopolysaccharide, which reached a concentration of 8.9 g/L at the end of the culture, and an intracellular granular structure which was detected by transmission electron microscopy, suggesting the accumulation of polyhydroxyalkanoate, most likely polyhydroxybutyrate.
Novelty and scientific contribution. M. organophilum demonstrated a unique ability to produce compounds of commercial interest, leading to a genuine understanding that this species has a metabolism distint. The use of Methylobacterium organophilum makes room for platform integration in the context of biorefineries as a result of its distinct metabolic diversity.