Contributions of citrate in redox potential maintenance and ATP production: metabolic pathways and their regulation in Lactobacillus panis PM1

Kang, Tae Seok; Korber, Darren R.; Tanaka, Takuji

doi:10.1007/s00253-013-5108-2

Cited by 26 publications

(26 citation statements)

References 31 publications

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“…6) and altered fructose metabolism from heterolactic to homolactic fermentation, wherein most fructose was processed to lactate. Also, citrate (initial concentration, 16.03 mM) was not converted to succinate, which is an alternate NAD ϩ regeneration route for the 6-PG/PK pathway in the presence of citrate (11), suggesting no NADH regeneration provision from this pathway. Therefore, this change in fermentation pattern indicated that in this recombinant PM1 strain, fructose was mostly fermented via the EM pathway, generating 2 ATP molecules per fructose molecule.…”

Section: Discussionmentioning

confidence: 99%

“…The PM1-TPI strain also produced approximately 11 mM ethanol from fructose fermentation. This ethanol may have been produced via two possible routes: (i) the pyruvate-to-acetyl coenzyme A pathway from the activity of pyruvate dehydrogenase (11) or (ii) the 6-PG/PK pathway via the activity of PGI (Fig. 7).…”

Section: Discussionmentioning

confidence: 99%

“…The amplified TPI gene was digested with NotI and SalI restriction endonucleases and cloned into the expression vector pCER-EGFP ( Table 2). The resultant plasmids were transformed into L. panis PM1 by electroporation, as described previously (11).…”

Section: Determination Of Hexoses (Glucose and Fructose) And End Prodmentioning

confidence: 99%

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Regulation of Dual Glycolytic Pathways for Fructose Metabolism in Heterofermentative Lactobacillus panis PM1

Kang

Korber

Tanaka

2013

Appl Environ Microbiol

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Lactobacillus panis PM1 belongs to the group III heterofermentative lactobacilli that use the 6-phosphogluconate/phosphoketolase (6-PG/PK) pathway as their central metabolic pathway and are reportedly unable to grow on fructose as a sole carbon source. We isolated a variant PM1 strain capable of sporadic growth on fructose medium and observed its distinctive characteristics of fructose metabolism. The end product pattern was different from what is expected in typical group III lactobacilli using the 6-PG/PK pathway (i.e., more lactate, less acetate, and no mannitol). In addition, in silico analysis revealed the presence of genes encoding most of critical enzymes in the Embden-Meyerhof (EM) pathway. These observations indicated that fructose was metabolized via two pathways. Fructose metabolism in the PM1 strain was influenced by the activities of two enzymes, triosephosphate isomerase (TPI) and glucose 6-phosphate isomerase (PGI). A lack of TPI resulted in the intracellular accumulation of dihydroxyacetone phosphate (DHAP) in PM1, the toxicity of which caused early growth cessation during fructose fermentation. The activity of PGI was enhanced by the presence of glyceraldehyde 3-phosphate (GAP), which allowed additional fructose to enter into the 6-PG/PK pathway to avoid toxicity by DHAP. Exogenous TPI gene expression shifted fructose metabolism from heterolactic to homolactic fermentation, indicating that TPI enabled the PM1 strain to mainly use the EM pathway for fructose fermentation. These findings clearly demonstrate that the balance in the accumulation of GAP and DHAP determines the fate of fructose metabolism and the activity of TPI plays a critical role during fructose fermentation via the EM pathway in L. panis PM1. L actobacilli generate metabolic energy (i.e., ATP) mainly by substrate-level phosphorylation by relatively simple pathways: the Embden-Meyerhof (EM) pathway and/or the 6-phosphogluconate/phosphoketolase (6-PG/PK) pathway. The members of the genus Lactobacillus are subdivided into three groups according to their fermentative characteristics on the basis of the presence of these pathways (1, 2). Group I lactobacilli are obligatory homofermentative lactobacilli that exclusively ferment hexose sugars (e.g., glucose) to lactate via the EM pathway; however, they do not metabolize pentose sugars or gluconate. Group II lactobacilli are the facultative heterofermentative lactobacilli that ferment hexoses to lactate via the EM pathway. They can also ferment pentose sugars using an inducible phosphoketolase, producing lactate and acetate, and they can yield carbon dioxide from gluconate but not from glucose. Group III lactobacilli are the obligatory heterofermentative lactobacilli that ferment hexoses to lactate, ethanol and/or acetate, and carbon dioxide, which is a distinct feature of the group III lactobacilli. Group III lactobacilli exclusively use the 6-PG/PK pathway to achieve this metabolism.Fructose, an abundant hexose sugar found in many plants, is one of the main monosaccharides for bacteria...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Regulation of Dual Glycolytic Pathways for Fructose Metabolism in Heterofermentative Lactobacillus panis PM1

Kang

Korber

Tanaka

2013

Appl Environ Microbiol

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“…These data indicated that the acetic acid-to-ethanol route was insufficient for NAD ϩ regeneration during the rapid glycerol consumption period (from 48 h to 72 h). Ethanol production is a typical NAD ϩ regeneration route, and the pyruvate-to-ethanol route (via acetyl coenzyme A) has previously been reported in L. panis PM1 (15). Thus, a part of the pyruvate formed from glycerol could be directed to ethanol production due to the limited capacity of lactate dehydrogenase for NAD ϩ regeneration ( Fig.…”

Section: Resultsmentioning

confidence: 99%

“…2), respectively. These plasmids were then transformed into L. panis PM1 by the electroporation method, as described previously (15).…”

Section: Figmentioning

confidence: 99%

Metabolic Engineering of a Glycerol-Oxidative Pathway in Lactobacillus panis PM1 for Utilization of Bioethanol Thin Stillage: Potential To Produce Platform Chemicals from Glycerol

Kang

Korber

Tanaka

2014

Appl Environ Microbiol

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Lactobacillus panis PM1 has the ability to produce 1,3-propanediol (1,3-PDO) from thin stillage (TS), which is the major waste material after bioethanol production, and is therefore of significance. However, the fact that L. panis PM1 cannot use glycerol as a sole carbon source presents a considerable problem in terms of utilization of this strain in a wide range of industrial applications. Accordingly, L. panis PM1 was genetically engineered to directly utilize TS as a fermentable substrate for the production of valuable platform chemicals without the need for exogenous nutrient supplementation (e.g., sugars and nitrogen sources). An artificial glycerol-oxidative pathway, comprised of glycerol facilitator, glycerol kinase, glycerol 3-phosphate dehydrogenase, triosephosphate isomerase, and NADPH-dependent aldehyde reductase genes of Escherichia coli, was introduced into L. panis PM1 in order to directly utilize glycerol for the production of energy for growth and value-added chemicals. A pH 6.5 culture converted glycerol to mainly lactic acid (85.43 mM), whereas a significant amount of 1,3-propanediol (59.96 mM) was formed at pH 7.5. Regardless of the pH, ethanol (82.16 to 83.22 mM) was produced from TS fermentations, confirming that the artificial pathway metabolized glycerol for energy production and converted it into lactic acid or 1,3-PDO and ethanol in a pH-dependent manner. This study demonstrates the cost-effective conversion of TS to value-added chemicals by the engineered PM1 strain cultured under industrial conditions. Thus, application of this strain or these research findings can contribute to reduced costs of bioethanol production.T hin stillage (TS) is a major fermentation residue from the dry-grind process of bioethanol production. Its downstream treatment, including making a condensed form for animal feed, is an energy-and cost-intensive process (1), while its utilization as animal feed is hardly a high-value application of this industrial by-product and hence does not significantly reduce the cost of ethanol production. TS contains a variety of complex nutrients, including various carbohydrates, minerals, and amino acids. Glycerol (up to 2%) is generated in TS during bioethanol production regardless of feedstock (i.e., sugar cane or corn) (2). Glycerol is at a higher reduced state than carbohydrates (i.e., fermentable sugars). The reduced nature of glycerol allows synthesis of fuels and other reduced chemicals at higher yields with minimal by-products compared to common sugars (e.g., glucose and xylose); however, the high degree of reduction in glycerol makes it difficult for microorganisms to utilize under anaerobic conditions. A few bacteria, including Klebsiella, Enterobacter, and Clostridium, have been exploited to bioconvert glycerol to industrially relevant chemicals (e.g., 1,3-propanediol [1,3-PDO], 3-hydroxypropionic acid, butanol, and ethanol) (3-7). Since these organisms are classified as opportunistic pathogens, industrial applications of these strains may pose issues, particularly re...

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Metabolism and biochemistry of LAB and dairy‐associated species

Poltronieri

Battelli

Mangia

2017

Microbiology in Dairy Processing

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Contributions of citrate in redox potential maintenance and ATP production: metabolic pathways and their regulation in Lactobacillus panis PM1

Cited by 26 publications

References 31 publications

Regulation of Dual Glycolytic Pathways for Fructose Metabolism in Heterofermentative Lactobacillus panis PM1

Regulation of Dual Glycolytic Pathways for Fructose Metabolism in Heterofermentative Lactobacillus panis PM1

Metabolic Engineering of a Glycerol-Oxidative Pathway in Lactobacillus panis PM1 for Utilization of Bioethanol Thin Stillage: Potential To Produce Platform Chemicals from Glycerol

Metabolism and biochemistry of LAB and dairy‐associated species

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