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      Enhanced propionic acid production from whey lactose with immobilized Propionibacterium acidipropionici and the role of trehalose synthesis in acid tolerance

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          Abstract

          High propionic acid production could be achieved with an enhanced trehalose synthesis mutant immobilized on PEI-Poraver in FBB fed-batch fermentation.

          Whey lactose is a major by-product of the cheese and casein manufacturing industry. Utilization of this cheap and renewable resource is an area of interest among biotechnologists and bulk chemists. The objective of the present work was to determine the suitability of whey lactose for propionic acid production by a food microbe, Propionibacterium acidipropionici. Batch and fed-batch fermentations of whey lactose with both free cells and immobilized cells in a fibrous bed bioreactor (FBB) were examined and compared. It was observed that cells immobilized on polyethylenimine-treated Poraver (PEI-Poraver) in FBB favored higher productivity and yield of propionic acid as compared to free-cell fermentation. Interestingly, P. acidipropionici accumulated high levels of trehalose, especially in response to acid stress. An analysis of the P. acidipropionici genome sequence revealed the presence of two putative trehalose biosynthesis pathways (OtsA–OtsB and TreY–TreZ), and their functions in response to acid stress were subsequently studied. To further improve propionic acid production, an enhanced trehalose synthesis mutant was obtained by over-expression of an otsA gene encoding enzyme belonging to the OtsA–OtsB pathway. In this mutant, the maximum concentration of propionic acid reached 135 ± 6.5 g L −1 in a fed-batch fermentation approach, which to our knowledge is among the highest propionic acid concentration ever produced in the traditional fermentation process. In view of these results it was concluded that the FBB fed-batch fermentation with an enhanced trehalose synthesis mutant from whey lactose can therefore be considered as a good candidate for the large-scale production of propionic acid in the near future.

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          Most cited references 40

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          Biological effects of propionic acid in humans; metabolism, potential applications and underlying mechanisms.

          Undigested food is fermented in the colon by the microbiota and gives rise to various microbial metabolites. Short-chain fatty acids (SCFA), including acetic, propionic and butyric acid, are the principal metabolites produced. However, most of the literature focuses on butyrate and to a lesser extent on acetate; consequently, potential effects of propionic acid (PA) on physiology and pathology have long been underestimated. It has been demonstrated that PA lowers fatty acids content in liver and plasma, reduces food intake, exerts immunosuppressive actions and probably improves tissue insulin sensitivity. Thus increased production of PA by the microbiota might be considered beneficial in the context of prevention of obesity and diabetes type 2. The molecular mechanisms by which PA may exert this plethora of physiological effects are slowly being elucidated and include intestinal cyclooxygenase enzyme, the G-protein coupled receptors 41 and 43 and activation of the peroxisome proliferator-activated receptor γ, in turn inhibiting the sentinel transcription factor NF-κB and thus increasing the threshold for inflammatory responses in general. Taken together, PA emerges as a major mediator in the link between nutrition, gut microbiota and physiology. Copyright © 2010 Elsevier B.V. All rights reserved.
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            Physiological roles of trehalose in bacteria and yeasts: a comparative analysis.

             J Arguelles (2000)
            The disaccharide trehalose is widely distributed in nature and can be found in many organisms, including bacteria, fungi, plants, invertebrates and mammals. Due to its particular physical features, trehalose is able to protect the integrity of the cell against a variety of environmental injuries and nutritional limitations. In addition, data available on several species of bacteria and yeast suggest specific functions for trehalose in these organisms. Bacteria can use exogenous trehalose as the sole source of carbon and energy as well as synthesize enormous amounts of the disaccharide as compatible solute. This ability to accumulate trehalose is the result of an elaborate genetic system, which is regulated by osmolarity. Some mycobacteria contain sterified trehalose as a structural component of the cell wall, whereas yeast cells are largely unable to grow on trehalose as carbon source. In these lower eukaryotes, trehalose appears to play a dual function: as a reserve compound, mainly stored in vegetative resting cells and reproductive structures, and as a stress metabolite. Recent findings also point to important biotechnological applications for trehalose.
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              Trehalose synthesis is induced upon exposure of Escherichia coli to cold and is essential for viability at low temperatures.

              Trehalose accumulates dramatically in microorganisms during heat shock and osmotic stress and helps protect cells against thermal injury and oxygen radicals. Here we demonstrate an important role of this sugar in cold-adaptation of bacteria. A mutant Escherichia coli strain unable to produce trehalose died much faster than the wild type at 4 degrees C. Transformation of the mutant with the otsA/otsB genes, responsible for trehalose synthesis, restored trehalose content and cell viability at 4 degrees C. After temperature downshift from 37 degrees C to 16 degrees C ("cold shock"), trehalose levels in wild-type cells increased up to 8-fold. Although this accumulation of trehalose did not influence growth at 16 degrees C, it enhanced cell viability when the temperature fell further to 4 degrees C. Before the trehalose build-up, levels of mRNA encoding OtsA/OtsB increased markedly. This induction required the sigma factor, RpoS, but was independent of the major cold-shock protein, CspA. otsA/B mRNA was much more stable at 16 degrees C than at 37 degrees C and contained a "downstream box," characteristic of cold-inducible mRNAs. Thus, otsA/otsB induction and trehalose synthesis are activated during cold shock (as well as during heat shock) and play an important role in resistance of E. coli (and probably other organisms) to low temperatures.
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                Author and article information

                Journal
                GRCHFJ
                Green Chemistry
                Green Chem.
                Royal Society of Chemistry (RSC)
                1463-9262
                1463-9270
                2015
                2015
                : 17
                : 1
                : 250-259
                Article
                10.1039/C4GC01256A
                © 2015
                Product
                Self URI (article page): http://xlink.rsc.org/?DOI=C4GC01256A

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