Improved propionic acid production with metabolically engineered Propionibacterium jensenii by an oxidoreduction potential-shift control strategy

Appl Microbiol Biotechnol

Liu

2019

Self Cite

362

194

Microorganisms encounter acid stress during multiple bioprocesses. Microbial species have therefore developed a variety of resistance mechanisms. The damage caused by acidic environments is mitigated through the maintenance of pH homeostasis, cell membrane integrity and fluidity, metabolic regulation, and macromolecule repair. The acid tolerance mechanisms can be used to protect probiotics against gastric acids during the process of food intake, and can enhance the biosynthesis of organic acids. The combination of systems and synthetic biology technologies offers new and wide prospects for the industrial applications of microbial acid tolerance mechanisms. In this review, we summarize acid stress response mechanisms of microbial cells, illustrate the application of microbial acid tolerance in industry, and prospect the introduction of systems and synthetic biology to further explore the acid tolerance mechanisms and construct a microbial cell factory for valuable chemicals.

Section: Enhancement Of Organic Acid Production By Acid-tolerant Strainsmentioning

confidence: 99%

Microbial response to acid stress: mechanisms and applications

Appl Microbiol Biotechnol

Liu

2019

Self Cite

362

194

“…Propionibacteria are major producers of PA, owing to the vitality, high yield, wide variety of substrates used, “generally regarded as safe” designation, and antimicrobial activity (Guan et al, ). Various strategies have been developed to improve PA yield and increase productivity of propionibacteria, including optimization of carbon sources (Coral et al, ) and fermentation modes (Zhu et al, ), control of culture conditions such as pH (Zhuge et al, ) and oxidoreduction potential (Zhuge et al, ), reductions in by‐product accumulation (Zhang & Yang, ), and engineering of metabolic pathways (Liu et al, , ; Wang et al, ). Despite all of this, microbial production of PA is still unable to meet industrial standards and market demand.…”

Section: Introductionmentioning

confidence: 99%

Comparative genomics and transcriptomics analysis‐guided metabolic engineering of Propionibacterium acidipropionici for improved propionic acid production

Biotech & Bioengineering

et al. 2017

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Acid stress induced by the accumulation of organic acids during the fermentation of propionibacteria is a severe limitation in the microbial production of propionic acid (PA). To enhance the acid resistance of strains, the tolerance mechanisms of cells must first be understood. In this study, comparative genomic and transcriptomic analyses were conducted on wild-type and acid-tolerant Propionibacterium acidipropionici to reveal the microbial response of cells to acid stress during fermentation. Combined with the results of previous proteomic and metabolomic studies, several potential acid-resistance mechanisms of P. acidipropionici were analyzed. Energy metabolism and transporter activity of cells were regulated to maintain pH homeostasis by balancing transmembrane transport of protons and ions; redundant protons were eliminated by enhancing the metabolism of certain amino acids for a relatively stable intracellular microenvironment; and protective mechanism of macromolecules were also induced to repair damage to proteins and DNA by acids. Transcriptomic data indicated that the synthesis of acetate and lactate were undesirable in the acid-resistant mutant, the expression of which was 2.21-fold downregulated. In addition, metabolomic data suggested that the accumulation of lactic acid and acetic acid reduced the carbon flow to PA and led to a decrease in pH. On this basis, we propose a metabolic engineering strategy to regulate the synthesis of lactic acid and acetic acid that will reduce by-products significantly and increase the PA yield by 12.2% to 10.31 ± 0.84 g/g DCW. Results of this study provide valuable guidance to understand the response of bacteria to acid stress and to construct microbial cell factories to produce organic acids by combining systems biology technologies with synthetic biology tools.

“…Various strategies have been proposed to improve the fermentation process and enhance PA synthesis 3 . However, the majority of these efforts involve strain evolution 28 29 and fermentation optimization 16 19 . Metabolic engineering of propionibacteria has progressed slowly due to the lack of genome information, the shortage of available gene manipulation tools, the difficulties of transforming gram-positive bacteria, and the high GC content of genomes 5 .…”

Section: Discussionmentioning

confidence: 99%

“…A range of carbon sources including glucose 6 , xylose 7 , lactose 8 , sucrose 9 , lactic acid 10 , and maltose 11 and many renewable and low-cost substrates such as hemicellulose 12 , sweet whey permeate 13 , corn meal 14 , and cane molasses 15 can be used by propionibacteria to synthetize PA. In addition, fed-batch culture 16 , extractive fermentation 17 , cell immobilization 11 , pH-shift control 18 , oxidoreduction potential-shift control 19 , and plant fibrous-bed bioreactor 20 techniques have been developed to improve PA production.…”

mentioning

confidence: 99%

Pathway engineering of Propionibacterium jensenii for improved production of propionic acid

Liu

Zhu

et al. 2016

Sci Rep

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Propionic acid (PA) is an important chemical building block widely used in the food, pharmaceutical, and chemical industries. In our previous study, a shuttle vector was developed as a useful tool for engineering Propionibacterium jensenii, and two key enzymes—glycerol dehydrogenase and malate dehydrogenase—were overexpressed to improve PA titer. Here, we aimed to improve PA production further via the pathway engineering of P. jensenii. First, the phosphoenolpyruvate carboxylase gene (ppc) from Klebsiella pneumoniae was overexpressed to access the one-step synthesis of oxaloacetate directly from phosphoenolpyruvate without pyruvate as intermediate. Next, genes encoding lactate dehydrogenase (ldh) and pyruvate oxidase (poxB) were deleted to block the synthesis of the by-products lactic acid and acetic acid, respectively. Overexpression of ppc and deleting ldh improved PA titer from 26.95 ± 1.21 g·L−1 to 33.21 ± 1.92 g·L−1 and 30.50 ± 1.63 g·L−1, whereas poxB deletion decreased it. The influence of this pathway engineering on gene transcription, enzyme expression, NADH/NAD+ ratio, and metabolite concentration was also investigated. Finally, PA production in P. jensenii with ppc overexpression as well as ldh deletion was investigated, which resulted in further increases in PA titer to 34.93 ± 2.99 g·L−1 in a fed-batch culture.