Selective production of the acyclic monoterpene β-myrcene by microplantlet suspension cultures of the macrophytic marine red alga Ochtodes secundiramea under nutrient perfusion cultivation with bromide-free medium

Abstract

This study demonstrated the selective production of a single acyclic monoterpene, β-myrcene, by photosynthetic, clonal microplantlet suspension cultures of the macrophytic red alga Ochtodes secundiramea (Cryptonemiales, Rhizophyllidaceae). Microplantlets were cultivated within an airlift photobioreactor under continuous medium perfusion with enhanced nutrients (nitrate, phosphate) and 3500 ppm CO2 in the aeration gas to provide nutrient-replete conditions. The removal of bromide (Br-) and vanadate (VO43−) from the medium shut down bromoperoxidase-catalyzed halogenation, so that only the common precursor to halogenated monoterpenes, β-myrcene, accumulated within the biomass. Nutrient-replete cultivation enabled near-exponential biomass production to density of 6 g DW/L, with specific growth rate of 4.4 ± 0.1% per day over the 36 day cultivation period at near-saturation light intensity. Myrcene was produced during biomass production, and the specific rate of β-myrcene production within the biomass exceeded the specific rate of biomass production, so that β-myrcene accumulated within the biomass. Increasing the mean light intensity from approximately 60 to 95% of light saturation linearly increased the growth rate, but did not increase the specific rate of β-myrcene production. At near saturation light intensity, the specific rate of β-myrcene production was 6.8 ± 0.7% per day (1.0 S.E.) with yield of 40 μmol/g DW after 36 days. Although the yields of β-myrcene were low (0.6 wt% in biomass), the potential for high biomass density, ease of microplantlet separation, and high selectivity of hydrocarbon biosynthesis suggest that microplantlets of terpenoid-producing red macroalgae have promise as a new platform for advanced hydrocarbon biofuel production from CO2, provided new strategies can be developed to enhance monoterpene yield.