High productivity of ectoines by Halomonas boliviensis using a combined two-step fed-batch culture and milking process

A process comprising two-step fed-batch cultivation has been investigated for the production of ectoines using the halophilic bacterium Halomonas boliviensis DSM 15516T. The first cultivation was performed under optimal conditions for cell growth and resulted in cell mass concentration of about 41 g l−1 after 24 h of cultivation. During the second cultivation at higher salt concentration, accumulation of ectoines increased while cell mass decreased with increasing salt concentration. Maximum productivity of total ectoines reached was 10 g l−1 d−1 with ectoine concentration of 6 g l−1 and hydroxyectoine concentration of 8 g l−1 after 9 h of cultivation at 18.5% NaCl, which is among the highest reported so far. H. boliviensis cells were further recycled for the production process after releasing the ectoines. About 75% of the accumulated ectoines were released by subjecting the cells to hypoosmotic shock. On subsequent reincubation in a medium containing higher salt concentration the cells were able to re-synthesize the ectoines resulting in a global productivity of 11.1 g l−1 d−1, and ectoine and hydroxyectoine productivities of 9.1 g l−1 d−1 and 2.0 g l−1 d−1, respectively.