Combinatorial metabolic engineering of industrial Gluconobacter oxydans DSM2343 for boosting 5-keto-D-gluconic acid accumulation.

Jianfeng Yuan,Jianping Lin,Mianbin Wu,Lirong Yang

doi:10.1186/s12896-016-0272-y

Abstract

BackgroundL-(+)-tartaric acid (L-TA) is an important organic acid, which is produced from the cream of tartar or stereospecific hydrolysis of the cis-epoxysuccinate. The former method is limited by the availability of raw material and the latter is dependent on the petrochemical material. Thus, new processes for the economical preparation of L-TA from carbohydrate or renewable resource would be much more attractive. Production of 5-keto-D-gluconate (5-KGA) from glucose by Gluconobacter oxydans is the first step to produce L-TA. The aim of this work is to enhance 5-KGA accumulation using combinatorial metabolic engineering strategies in G. oxydans. The sldAB gene, encoding sorbitol dehydrogenase, was overexpressed in an industrial strain G. oxydans ZJU2 under a carefully selected promoter, P0169. To enhance the efficiency of the oxidation by sldAB, the coenzyme pyrroloquinoline quinone (PQQ) and respiratory chain were engineered. Besides, the role in sldAB overexpression, coenzyme and respiratory chain engineering and their subsequent effects on 5-KGA production were investigated.ResultsAn efficient, stable recombinant strain was constructed, whereas the 5-KGA production could be enhanced. By self-overexpressing the sldAB gene in G. oxydans ZJU2 under the constitutive promoter P0169, the resulting strain, G. oxydans ZJU3, produced 122.48 ± 0.41 g/L of 5-KGA. Furthermore, through the coenzyme and respiratory chain engineering, the titer and productivity of 5-KGA reached 144.52 ± 2.94 g/L and 2.26 g/(L · h), respectively, in a 15 L fermenter. It could be further improved the 5-KGA titer by 12.10 % through the fed-batch fermentation under the pH shift and dissolved oxygen tension (DOT) control condition, obtained 162 ± 2.12 g/L with the productivity of 2.53 g/(L · h) within 64 h.ConclusionsThe 5-KGA production could be significantly enhanced with the combinatorial metabolic engineering strategy in Gluconobacter strain, including sldAB overexpression, coenzyme and respiratory chain engineering. Fed-batch fermentation could further enlarge the positive effect and increase the 5-KGA production. All of these demonstrated that the robust recombinant strain can efficiently produce 5-KGA in larger scale to fulfill the industrial production of L-TA from 5-KGA.

Highlights

L-(+)-tartaric acid (L-TA) is an important organic acid, which is produced from the cream of tartar or stereospecific hydrolysis of the cis-epoxysuccinate
Promoter selection in G. oxydans strain Increasing interest in Gluconobacter has led to investigations on strain improvement
To select the appropriate promoter for gene expression in G. oxydans, we generated the different promoters in front of a gfp report gene in a pBBR1MCS5 vector

Summary

Introduction

L-(+)-tartaric acid (L-TA) is an important organic acid, which is produced from the cream of tartar or stereospecific hydrolysis of the cis-epoxysuccinate. The former method is limited by the availability of raw material and the latter is dependent on the petrochemical material. The LTA that is commercially available is produced exclusively through the stereospecific hydrolysis of cis-epoxysuccinate [5,6,7]. In this process, the reaction is catalyzed by the cis-epoxysuccinate hydrolase from Rhodococcus rhodochrous, Nocardia tartaricans, Corynebacterium sp. Development of the sustainable alternative solution for LTA manufacture has recently attracted increasing attention

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