Membrane-based continuous fermentation with cell recycling for propionic acid production from glycerol by Acidipropionibacterium acidipropionici.

BACKGROUND: Microbial production of propionic acid (PA) from renewable resources is limited by the slow growth of the producer bacteria and product-mediated inhibition. The present study evaluates high cell density continuous PA fermentation from glycerol (Gly) using Acidipropionibacterium acidipropionici DSM 4900 in a membrane-based cell recycling system. A ceramic tubular membrane filter of 0.22 µm pore size was used as the filtering device for cell recycling. The continuous fermentations were run sequentially at dilution rates of 0.05 and 0.025 1/h using varying glycerol concentrations and two different yeast extract concentrations. RESULTS: PA volumetric productivity of 0.98 g/L.h with a product yield of 0.38 gPA/gGly was obtained with 51.40 g/L glycerol at a yeast extract concentration of 10 g/L. Increasing the glycerol and yeast extract concentrations to 64.50 g/L and 20 g/L, respectively, increased in PA productivity, product yield, and concentration to 1.82 g/L.h, 0.79 gPA/gGly, and 38.37 g/L, respectively. However, lowering the dilution rate to 0.025 1/h reduced the production efficiency. The cell density increased from 5.80 to 91.83 gCDW/L throughout the operation, which lasted for a period of 5 months. A tolerant variant of A. acidipropoinici exhibiting growth at a PA concentration of 20 g/L was isolated at the end of the experiment. CONCLUSIONS: Applying the current approach for PA fermentation can overcome several limitations for process industrialization.

Dióxido de cloro, los milagros no existen / Chlorine dioxide, miricles do not exist

OBJETIVOS: contribuir con una revisión bibliográfica acerca de la acción del dióxido de cloro sobre ciertos microorganismos y biomoléculas. Hacer una revisión de sus usos, toxicidad, reactividad química y bioquímica además de los estudios llevados adelante en modelos animales. Entender cuál es el alcance de los estudios en modelos animales y relacionarlos con la posibilidad de realizar estudios en humanos. METODOLOGÍA: se realizó una revisión exhaustiva sobre el dióxido de cloro. Su uso como antiséptico, toxicidad, estructura molecular, generación de oxígeno molecular, reactividad con biomoléculas y experimentos en modelos animales para entender cuál es el estado del arte de las investigaciones sobre esta molécula. Todas las búsquedas fueron realizadas en bases de datos de artículos científicos así como también por intercambio de información con profesionales entendidos en el tema y curiosidades del colectivo popular. RESULTADOS: la estructura y reactividad molecular del dióxido de cloro determinan una reactividad alta con ciertos aminoácidos y proteínas, explicando así su actividad biológica inhibitoria. Varios estudios demostraron esta actividad inhibitoria frente a diferentes microorganismos, incluyendo los virus. Tales datos y un ensayo clínico en humanos determinaron una baja toxicidad a bajas concentraciones. Sin embargo, pese a tales evidencias, la falta de más estudios clínicos en situaciones controladas inviabiliza la posibilidad de extrapolar los datos al ser humano para mitigar enfermedades infecciosas como el Covid-19. CONCLUSIONES: la reactividad del dióxido de cloro queda clara y su acción sobre las proteínas explica su efectiva acción contra microorganismos como los virus. Su baja toxicidad en estudios llevados adelante en modelos animales abre la posibilidad de más estudios clínicos. Extrapolar los datos que se tienen hasta ahora al ser humano no es correcto.

OBJECTIVES: to contribute with a bibliographic review about the action of chlorine dioxide on certain microorganisms and biomolecules. To review its uses, toxicity, chemical and biochemical reactivity besides studies carried out in animal models. To understand what the extent of the studies in animal models is and relate them with the possibility of carrying out studies in humans. METHODOLOGY: an exhaustive review has been done about chlorine dioxide. Its use as an antiseptic, toxicity, molecular structure, molecular oxygen generation, reactivity with biomolecules and experiments on animal models to understand at which state of the art the research on this molecule is. Every search was carried out in data bases of scientific papers as well as by information exchange with professionals of the field and certain curiosities of the popular collective. RESULTS: The structure and molecular reactivity of chlorine dioxide determines a high reactivity with certain aminoacids and proteins, therefore explaining its inhibitory biological activity. Several studies demonstrated this inhibitory activity against different microorganisms, including viruses. These data and a clinical assay in humans determined a low toxicity at low concentrations. Nonetheless, the lack of more human clinical studies in controlled situations prevents it from the possibility to extrapolate those data to human beings in order to mitigate infectious diseases like Covid-19. CONCLUSIONS: the reactivity of chlorine dioxide remains clarified and its action on proteins explains the effective action against microorganisms like viruses. Its low toxicity in studies carried out in animal models opens the possibility of more clinical studies. Extrapolate data obtained so far to human beings is not correct.

Stress induced biofilm formation in Propionibacterium acidipropionici and use in propionic acid production.

Propionibacterium acidipropionici produces propionic acid from different sugars and glycerol; the production can be improved by high cell density fermentations using immobilized cells that help to overcome the limitations of the non-productive lag phase and product inhibition. In this study, the use of stress factors to induce P. acidipropionici to form biofilm and its use as an immobilization procedure in fermentations in bioreactors for producing propionic acid was investigated. Citric acid and sodium chloride increased exopolysaccharide production, biofilm forming capacity index and trehalose production. Analysis of the expression of trehalose synthesis-related genes otsA and treY by RT-qPCR showed significantly increased expression of only treY during log phase with citric acid, while FISH analysis showed expression of treY and luxS under the influence of both stress factors. The stress factors were then used for development of microbial biofilms as immobilization procedure on Poraver® and AnoxKaldnes® carriers in recycle batch reactors for propionic acid production from 20 g/L glycerol. Highest productivities of 0.7 and 0.78 g/L/h were obtained in Poraver® reactors, and 0.39 and 0.43 g/L/h in AnoxKaldnes® reactors with citric acid and NaCl, respectively.