Spaceflight‐induced enhancement of 2‐keto‐L‐gulonic acid production by a mixed culture of Ketogulonigenium vulgare and Bacillus thuringiensis

Two bacterial strains used for industrial production of 2‐keto‐L‐gulonic acid (2‐KLG), Ketogulonigenium vulgare 2 and Bacillus thuringiensis 1514, were loaded onto the spacecraft Shenzhou VII and exposed to space conditions for 68 h in an attempt to increase their fermentation productivities of 2‐KLG. An optimal combination of mutants B. thuringiensis 320 and K. vulgare 2194 (KB2194‐320) was identified by systematically screening the pH and 2‐KLG production of 16 000 colonies. Compared with the coculture of parent strains, the conversion rate of L‐sorbose to 2‐KLG by KB2194‐320 in shake flask fermentation was increased significantly from 82·7% to 95·0%. Furthermore, a conversion rate of 94·5% and 2‐KLG productivity of 1·88 g l^?1 h^?1 were achieved with KB2194‐320 in industrial‐scale fermentation (260 m³ fermentor). An observed increase in cell number of K2194 (increased by 47·8%) during the exponential phase and decrease in 2‐KLG reductase activity (decreased by 46·0%) were assumed to explain the enhanced 2‐KLG production. The results suggested that the mutants KB2194‐320 could be ideal substitutes for the currently employed strains in the 2‐KLG fermentation process and demonstrated the feasibility of using spaceflight to breed high‐yielding 2‐KLG‐producing strains for vitamin C production.

Significance and Impact of the Study

KB2194‐320, a combination of two bacterial strains bred by spaceflight mutation, exhibited significantly improved 2‐KLG productivity and hence could potentially increase the efficiency and reduce the cost of vitamin C production by the two‐step fermentation process. In addition, a new pH indicator method was applied for rational screening of K2, which dramatically improved the efficiency of screening.