Revealing differences in metabolic flux distributions between a mutant strain and its parent strain Gluconacetobacter xylinus CGMCC 2955.

Cheng Zhong,Shi-Ru Jia,Miao Liu,Xiao-Ning Yang,Luciano Piergiovanni,Hui-Xia Zhu,Yuan-Yuan Jia,Fei Li,Arnold Driessen

doi:10.1371/journal.pone.0098772

Cheng Zhong, Shi-Ru Jia + Show 7 more

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https://doi.org/10.1371/journal.pone.0098772

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Abstract

A better understanding of metabolic fluxes is important for manipulating microbial metabolism toward desired end products, or away from undesirable by-products. A mutant strain, Gluconacetobacter xylinus AX2-16, was obtained by combined chemical mutation of the parent strain (G. xylinus CGMCC 2955) using DEC (diethyl sulfate) and LiCl. The highest bacterial cellulose production for this mutant was obtained at about 11.75 g/L, which was an increase of 62% compared with that by the parent strain. In contrast, gluconic acid (the main byproduct) concentration was only 5.71 g/L for mutant strain, which was 55.7% lower than that of parent strain. Metabolic flux analysis indicated that 40.1% of the carbon source was transformed to bacterial cellulose in mutant strain, compared with 24.2% for parent strain. Only 32.7% and 4.0% of the carbon source were converted into gluconic acid and acetic acid in mutant strain, compared with 58.5% and 9.5% of that in parent strain. In addition, a higher flux of tricarboxylic acid (TCA) cycle was obtained in mutant strain (57.0%) compared with parent strain (17.0%). It was also indicated from the flux analysis that more ATP was produced in mutant strain from pentose phosphate pathway (PPP) and TCA cycle. The enzymatic activity of succinate dehydrogenase (SDH), which is one of the key enzymes in TCA cycle, was 1.65-fold higher in mutant strain than that in parent strain at the end of culture. It was further validated by the measurement of ATPase that 3.53–6.41 fold higher enzymatic activity was obtained from mutant strain compared with parent strain.

Highlights

Plant-based cellulose, due to its abundance and low-cost, has attracted increasing attention in recent years [1,2]
It has been reported that cellulose production by G. xylinus on glucose medium was enhanced in batch culture when ethanol was present in the media [13]
Obtaining Mutant Strain with High Bacterial cellulose (BC) Productivity To reduce the amount of byproducts and improve BC yield, different groups have carried out various methods that are summarized as follows

Summary

Introduction

Plant-based cellulose, due to its abundance and low-cost, has attracted increasing attention in recent years [1,2]. Bacterial cellulose (BC) is an insoluble, extracellular polysaccharide that is produced by certain types of microorganisms, such as Acetobacter species [4]. It is a highly pure form of cellulose with a fine nano-scale structure and has been widely used in food and biomedical fields for various applications [5,6,7]. Investigations on developing cost-effective culture processes have been broadly carried out using Gluconacetobacter, Acetobacter etc., to obtain maximum productivity of BC [8,9]. It has been reported that cellulose production by G. xylinus on glucose medium was enhanced in batch culture when ethanol was present in the media [13]. There is limited knowledge regarding the metabolism of existing strains of Gluconacetobacter, which makes it difficult to understand the metabolic network and relate it to the production of interesting products (such as acetic acid, cellulose, etc.) [14,15]

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Conclusion