Influence of carbon sources on the viability and resuscitation of Acetobacter senegalensis during high-temperature gluconic acid fermentation

Abstract

Much research has been conducted about different types of fermentation at high temperature, but only a few of them have studied cell viability changes during high-temperature fermentation. In this study, Acetobacter senegalensis, a thermo-tolerant strain, was used for gluconic acid production at 38 °C. The influences of different carbon sources and physicochemical conditions on cell viability and the resuscitation of viable but nonculturable (VBNC) cells formed during fermentation were studied. Based on the obtained results, A. senegalensis could oxidize 95 g l glucose to gluconate at 38 °C (pH 5.5, yield 83%). However, despite the availability of carbon and nitrogen sources, the specific rates of glucose consumption (q) and gluconate production (q) reduced progressively. Interestingly, gradual q and q reduction coincided with gradual decrease in cellular dehydrogenase activity, cell envelope integrity, and cell culturability as well as with the formation of VBNC cells. Entry of cells into VBNC state during stationary phase partly stemmed from high fermentation temperature and long-term oxidation of glucose, because just about 48% of VBNC cells formed during stationary phase were resuscitated by supplementing the culture medium with an alternative favorite carbon source (low concentration of ethanol) and/or reducing incubation temperature to 30 °C. This indicates that ethanol, as a favorable carbon source, supports the repair of stressed cells. Since formation of VBNC cells is often inevitable during high-temperature fermentation, using an alternative carbon source together with changing physicochemical conditions may enable the resuscitation of VBNC cells and their use for several production cycles.

Effect of Sequential Acclimation to Various Carbon Sources on the Proteome of Acetobacter senegalensis LMG 23690T and Its Tolerance to Downstream Process Stresses

“…Colony formation took about 72–80 h. In addition, colony formation time did not changed over sequential passages. This may be as a result of pH drop due to the oxidation of glucose to gluconic acid (Shafiei et al, 2017). Since pH and other fermentation parameters could not be monitored and regulated in solid culture media, acclimation in liquid culture media was used as a complementary method.…”

“…Acetic acid bacteria (AAB) have been used in industrial production of vinegar, gluconic acid and L -sorbose (Singh and Kumar, 2007; De Roos and De Vuyst, 2018). They can potentially be used for the production of cellulose and other biological and pharmaceutical compounds (Adachi et al, 2003; Shafiei et al, 2017). Different strains of AAB are used in vinegar production.…”

Modified semi‐continuous fermentation for resuscitating nongrowing cells during high‐temperature gluconic acid production by Acetobacter senegalensis

“…Fermentation samples were subjected to centrifugation at 13 000 g for 10 min. The supernatant was filtered (0·45 µm) and the concentration of glucose and gluconic acid in the supernatant was determined by HPLC (Agilent 1110 equipped with a Supelcogel C610H column), as described previously (Shafiei et al ; Shafiei et al ).…”

“…It was used for vinegar production and vinegar starter production (Ndoye et al ; Shafiei et al ; Shafiei et al ; Shafiei et al ). In 2017, Shafiei and coworkers evaluated sodium gluconate production by A. senegalensis in the batch culture at 38°C; however, cells were not able neither to consume glucose nor to produce gluconic acid at the end of stationary phase (Shafiei et al ). In addition, it was found that the cells sampled from stationary‐phase exhibited improved growth on solid culture medium containing ethanol as the main carbon source (Shafiei et al ).…”

“…Based on our previous findings (Shafiei et al ), and the above‐mentioned problems about cell viability change during fermentation, the main aim of the present study was to find a feeding strategy which enable nongrowing cells to resume growth on glucose, and produce gluconic acid in sequential fermentation cycles. Finally, based on single‐cell analysis complemented with enzymatic activities and co‐factor pool determination, we found physiological differences between cells growing in exponential‐phase, in stationary‐phase and resuscitated cells.…”