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Monitoring of CO2 and O2 concentrations in the headspace of Sakaguchi flasks during liquid culture of microorganism

Takahashi, Masato, Aoyagi, Hideki
Applied microbiology and biotechnology 2018 v.102 no.15 pp. 6637-6645
Escherichia coli, Saccharomyces cerevisiae, absorbance, adsorbents, carbon dioxide, culture flasks, culture media, headspace analysis, liquids, monitoring, oxygen
CO₂ and O₂ in the Sakaguchi flask headspace during culture was monitored via circulation direct monitoring and sampling system (CDMSS), a device with circulation bypass system. In static culture with Saccharomyces cerevisiae (circulation rate, 50 mL/min), a vertical CO₂ concentration gradient (maximum gap ~ 2% (v/v) [height from the bottom of flask 45 mm, 7%; 155 mm, 5%]) in the Sakaguchi flask headspace was observed; no concentration O₂ gradient was observed. However, shake flask culture showed vertical gradient concentrations for both CO₂ and O₂ (maximum gap of CO₂ and O₂ concentrations: 2 and 4% [heights from the bottom of flask 115 mm, 6.0 and 9.5%; 175 mm, 4.0 and 13.5%], respectively). When the CDMSS circulation rate in the Sakaguchi flask headspace was 300 or 400 mL/min, the gaseous environment was uniformly distributed so that no vertical gradient concentration was observed. In shaking culture with Escherichia coli under these conditions, CO₂ was accumulated at high concentrations in the headspace and culture broth (maximum values 8%, in the headspace; 120 mg/L, in the culture broth). Most of the accumulated CO₂ in the headspace could be removed by inserting a column packed with CO₂ adsorbent at the bypass port of the CDMSS gaseous circulation. Thus, dissolved CO₂ was maintained at a lower concentration, and the final UOD (unit optical density) value of culture was increased compared with that of the control. This study is the first to demonstrate that vertical gradients of CO₂ and O₂ concentrations exist in the headspace of Sakaguchi flask during culture.