Background: The marine thermophilic bacterium Rhodothermus marinus can degrade many polysaccharides which makes it interesting as a future cell factory. Progress using this bacterium has, however, been hampered by limited knowledge on media and conditions for biomass production, often resulting in low cell yields and low productivity, highlighting the need to develop conditions that allow studies of the microbe on molecular level. This study presents development of defned conditions that support growth, combined with evaluation of production of carotenoids and exopolysaccharides (EPSs) by R. marinus strain DSM 16675.
Results: Two defned media were initially prepared: one including a low addition of yeast extract (modifed Wolfe’s medium) and one based on specifc components (defned medium base, DMB) to which two amino acids (N and Q), were added. Cultivation trials of R. marinus DSM 16675 in shake fasks, resulted in maximum cell densities (OD620 nm) of 2.36±0.057, cell dry weight (CDW) 1.2±0.14 mg/L, total carotenoids 0.59× 10–3 mg/L, and EPSs 1.72±0.03 mg/L using 2 g/L glucose in DMB. In Wolfe’s medium (supplemented by 0.05 g/L yeast extract and 2.5 g/L glucose), maximum OD620 nm was 2.07±0.05, CDW 1.05±0.07 mg/L, total carotenoids 0.39× 10–3 mg/L, and EPSs 1.74±0.2 mg/L. Growth trials at 5 g/L glucose in these media either failed or resulted in incomplete substrate utilization. To improve reproducibility and increase substrate utilization, a screening of macroelements (e.g. phosphate) in DMB, was combined with use of trace elements and vitamins of the modifed Wolfe’s medium. The resulting defned minimal R. marinus medium, (DRM), allowed reproducible cultivations to a fnal OD620nm of 6.6±0.05, CDW 2.85±0.07 mg/L, a maximum specifc growth rate (µmax) of 0.26 h−1 , total carotenoids 0.77× 10–3 mg/L and EPSs 3.4±0.17 mg/L in cultivations supplemented with up to 5 g/L glucose.
Conclusion: A minimal defned medium (DRM) was designed that resulted in reproducible growth and an almost doubled formation of both total carotenoids and EPSs. Such defned conditions, are necessary for systematic studies of metabolic pathways, to determine the specifc requirements for growth and fully characterize metabolite production.
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