| 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, beta-elemene, the Z and E isomers of 10-bromomyrcene, 3-chloro-10 E-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 muE m-2 s-1 for nutrient, bromide and vanadium delivery cultivations and the mean light intensity was set to 52.5, 125, and 240 muE 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 mumol 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-1 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 nmol Vanadium L-1, with the bromide concentration going to 1.1 to 1.4 mmol Bromide L-1. |
