Flow-cytometric assessment of damages to Acetobacter senegalensis during freeze-drying process and storage

Abstract

Downstream processes have great influences on bacterial starter production. Different modifications occur to cellular compounds during freeze-drying process and storage of bacterial starters. Consequently, viability and culturability (multiplication capacity) undergo some changes. In this study, the effects of freeze-drying process and storage conditions were examined on cell envelope integrity, respiration and culturability of <em>Acetobacter senegalensis</em>. Freezing of cells protected with mannitol (20% w/w) did not affect cell multiplication and respiration considerably; however, 19% of cells showed compromised cell envelope after freezing. After drying, 1.96×10<sup>11</sup> CFU/g were enumerated, indicating that about 34% of the cells could survive and keep their culturability. Drying of the cells induced further leakage in cell envelope and finally 81% of cells appeared as injured ones; however, 87% of the dried cells maintained their respiration capacity. Storage temperature had significant effect on cell multiplication ability; higher storage temperature (35°C) caused 8.59-log reduction in cell culturability after nine-month period of storage. Collapse of cell envelop integrity and respiration was observed at 35°C. At lower storage temperature (4°C), the culturability decreased about one-log reduction after nine months. Cell envelope integrity was subjected to minor changes during a period of nine month-storage at 4°C whereas a heterogeneous population of cells with different respiration capacity emerged at 4°C. These results indicate that a major part of cells undergone drying process and storage entered into viable but non-culturable state. In addition, usage of different culture media didn’t improve resuscitation. Besides, it seems that sub-lethal damages to cell envelope caused uptake of propidium iodide, however these kinds of injuries could not impress cell multiplications and respiration.

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

“…The obtained creams were mixed with mannitol (20% w/w). It was then used for freeze-drying process under the conditions previously described by Shafiei et al (2013b).…”

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

“…In the present study , Acetobacter senegalensis is used as a thermo‐tolerant acetic acid bacterium isolated from mango fruit (Ndoye 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 ).…”

The role of protein modifications in senescence of freeze-dried Acetobacter senegalensis during storage

“…Vinegar technology is one of those fermentation technologies which still suffer from the lack of cost-effective starter cultures [2] due to the genetic instability of acetic acid bacteria during preservation [3] and the susceptibility of cells to downstream processes [4,5]. …”

“…However, as with other drying methods, loss of viability is one of the main problems during freezing and drying processes as well as storage period [4]. …”