Levan from Leuconostoc citreum BD1707: production optimization and changes in molecular weight distribution during cultivation

Levan is a well-known homopolymer of fructose composed predominantly of β-(2, 6) fructofuranosyl linkages in the backbone with occasional β-(2, 1) linkages in the branch chains with varied applications. However, high production cost due to low yield of microbial levan has become a bottleneck for its...

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Published in:	BMC biotechnology 2021-02, Vol.21 (1), p.14-14, Article 14
Main Authors:	Han, Jin, Feng, Huafeng, Wang, Xiaohua, Liu, Zhenmin, Wu, Zhengjun
Format:	Article
Language:	eng
Subjects:	Bacteria Biopolymers Biosynthesis Chain branching Chemical synthesis Cultivation Distribution of molecular weight Electrophoresis Gel electrophoresis Gram-positive bacteria Leuconostoc citreum Leuconostoc citreum BD1707 Levan Levansucrase Linkages Mathematical optimization Methods Microorganisms Molecular weight Molecular weight distribution Optimization Peak values Physiological aspects Polyacrylamide Polymers Production costs Production processes Response surface methodology Size exclusion chromatography Sodium dodecyl sulfate Sodium lauryl sulfate Sucrose Sugars Tomatoes Variables Yield
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Summary:	Levan is a well-known homopolymer of fructose composed predominantly of β-(2, 6) fructofuranosyl linkages in the backbone with occasional β-(2, 1) linkages in the branch chains with varied applications. However, high production cost due to low yield of microbial levan has become a bottleneck for its practical applications. Furthermore, factors affecting the molecular mass of the synthesized levan by Leuconostoc spp. during prolonged cultivation is not fully elucidated. The cultivation condition for Leuconostoc citreum BD1707 to synthesize levan was optimized by single-factor experiments and subsequently with response surface methodology (RSM). The average molecular weight (Mw) of levan synthesized by the strain L.citreum BD1707 under the optimized cultivation conditions was monitored by high-performance size exclusion chromatography (HPSEC). Finally, the enzyme with levan-degrading activity was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The levan yield of BD1707 reached 34.86 g/L with a corresponding productivity of 7.47 g/L/d under the optimal cultivation conditions deduced by RSM, i.e., cultivation at 26 °C and 200 rpm for 112 h in tomato juice supplemented with 172 g/L sucrose with an initial pH value of 6.12. The Mw of levan reached a peak value of 2.320 × 10 Da at 6 h of cultivation under the optimized cultivation conditions and then gradually decreased to 8.809 × 10 Da after 120 h of cultivation. The levan yield of the strain L.citreum BD1707 could be sufficiently enhanced via cultivation condition optimization. The decrease in molecular mass of the synthesized levan was attributed predominantly to the hydrolytic activity of levansucrase secreted by L.citreum BD1707 during cultivation, with an estimated Mw of 130 KD by SDS-PAGE, while the effect of acid hydrolysis could be nearly neglected.
ISSN:	1472-6750 1472-6750