Abstract
Microbial levan is an important biopolymer with considerable potential in food and medical applications. Bacillus amyloliquefaciens NK-ΔLP strain can produce high-purity, low-molecular-weight levan, but production is relatively low. To enhance the production of levan, six extracellular protease genes (bpr, epr, mpr, vpr, nprE and aprE), together with the tasA gene (encoding the major biofilm matrix protein TasA) and the pgsBCA cluster (responsible for poly-γ-glutamic acid (γ-PGA) synthesis), were intentionally knocked out in the Bacillus amyloliquefaciens NK-1 strain. The highest levan production (31.1 g/L) was obtained from the NK-Q-7 strain (ΔtasA, Δbpr, Δepr, Δmpr, Δvpr, ΔnprE, ΔaprE and ΔpgsBCA), which was 103% higher than that of the NK-ΔLP strain (ΔpgsBCA) (15.3 g/L). Furthermore, the NK-Q-7 strain also showed a 94.1% increase in α-amylase production compared with NK-ΔLP strain, suggesting a positive effect of extracellular protease genes deficient on the production of endogenously secreted proteins. This is the first report of the improvement of levan production in microbes deficient in extracellular proteases and TasA, and the NK-Q-7 strain exhibits outstanding characteristics for extracellular protein production or extracellular protein related product synthesis.
Highlights
Microbial levan is an important biopolymer with considerable potential in food and medical applications
B. amyloliquefaciens NK-1 is derived from the LL3 strain, which was isolated from fermented food (Korea bibimbap paste)[9], it is safe for human beings
We found that the NK-1 strain could co-produce γ -PGA and levan simultaneously (Fig. 6a)
Summary
Microbial levan is an important biopolymer with considerable potential in food and medical applications. The NK-Q-7 strain showed a 94.1% increase in α-amylase production compared with NK-ΔLP strain, suggesting a positive effect of extracellular protease genes deficient on the production of endogenously secreted proteins. This is the first report of the improvement of levan production in microbes deficient in extracellular proteases and TasA, and the NK-Q-7 strain exhibits outstanding characteristics for extracellular protein production or extracellular protein related product synthesis. The sacC gene mutant strain showed three-fold higher levansucrase (SacB) activity than the wild-type strain and the levan titer increased from 15.5 g/L to 21.2 g/L. Ananthalakshmy et al.[16] expressed the sacB gene by using the pLSD19 plasmid in the sucrase mutant Zymomonas mobilis Zsuc[1] strain and found that levan production increased from 5 g/L to 10.7 g/L compared with the wild-type strain
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