Photolithotrophic cultivation of Laminaria japonica gametophyte cells in a silicone tubular membrane-aerated photobioreactor

Abstract

Gametophyte cells of brown algae Laminaria japonica were employed both in a modified silicone tubular membrane-aerated photobioreactor (bubble-less cultivation mode) and a bubble-column photobioreactor (bubbling cultivation mode), to study different gas–liquid mixing modes on cell growth rate and cell physiological status. With an inoculum density of 50 mg DCW l−1, in modified artificial Pacific seawater (APSW) medium at 13°C, light intensity of 60 μE m−2 s−1, light cycle of 16/8 h L/D, and aeration rate of 60 ml min−1, the specific growth rates were 0.082 d−1 for bubble-less mode and 0.070 d−1 for bubbling mode with biomass, in the form of dry cell density, increasing 10.9 and 6.8 times, respectively, during the 36 days’ photolithotrophic cultivation. The specific oxygen evolution rate under bubble-less mode was 39.6% higher than under bubbling mode on the 18th day. The gametophyte cells grew in cell aggregates with clump sizes, at day 36, of 1.5 mm and 0.5 mm diameter under bubble-less and bubbling mode respectively and cell injury percentages of 5.1% and 21.1%, respectively. The silicone tubular membrane-aerated photobioreactor was better suited for the cultivation of fragile macroalgal gametophyte cells due to the absence of hydrodynamic shear stress caused by fluid turbulence and the presence of a bubble-less gas supply.