- Halogenated monoterpene production by the red macroalga Octhodes
secundiramea was studied-under different levels of nutrient, bromide, vanadium
and light delivery. The key products formed were identified as myrcene, betaelemene,
the Z and E isomers of l0-bromomyrcene, 3-chloro-10E-bromomyrcene,
Apakaocthodene A, and isomers of chloromyrcene and dibromomyrcene. The
proposed pathway begins with an initial halogenation of myrcene to 3-
chloromyrcene or 10-bromomyrcene. 10-bromomyrcene reacts with either chloride
or bromide ions producing either 3-chloro-10E-bromomyrcene or 1,10-
dibromomyrcene. The production of Apakaochtodene A starts from myrcene with
4 consecutive halogenation reactions, the first one forming the cyclic ring.
All fermentations were carried out in similar 2L photobioreactors.
Temperature was controlled at 26°C, with a photoperiod of 14 hours on:10 hours
off. Incident light intensity was 143 μE m⁻² s⁻¹ for nutrient, bromide and vanadium
delivery cultivations and the mean light intensity was set to 52.5, 125, and 240 μE
m⁻² s⁻¹ for light delivery cultivations. The pH was buffered to 8.0 with sodium
bicarbonate, but not controlled. Air was supplied at 630 mL min⁻¹, vvm of 0.3, and
CO₂ was supplied at 2 mL min⁻¹ for nutrient and light delivery cultivations and 0
mL min⁻¹ for bromide and vanadium delivery cultivations. For nutrient delivery
cultivations, nitrate was delivered at 0.006, 0.076 and 0.74 mmol Nitrate L⁻¹ day⁻¹
and phosphate was delivered at 0.33, 3.99 and 38.4 μmol Phosphate L⁻¹ day⁻¹. For
semi-continuous delivery cultivations, bromide was delivered at 0.0, 0.0074, 0.013
and 0.13 mmol Bromide L⁻¹ day⁻¹ at a constant vanadium delivery of 6.38 to 7.35
nmol Vanadium L⁻¹ day⁻¹, and vanadium delivery was set to 0.0 and 6.38 nmol
Vanadium L⁻¹ day⁻' at a constant bromide delivery of 0.13 mmol Bromide L⁻¹ day⁻¹.
For fed-batch bromide and vanadium delivery cultivations the one time pulse of
bromide raised the medium bromide concentration to 0.0, 0.038, 0.128 and 1.4
mmol Bromide L⁻¹, with the vanadium concentration going to 416 to 520 nmol
Vandadium L⁻¹, and the pulse of vanadium raised the medium vanadium
concentration to 0.0 and 515 mmol Vanadium L⁻¹, with the bromide concentration
going to 1.1 to 1.4 mmol Bromide L⁻¹.