Screening and molecular characterization of new thermo‐ and ethanol‐tolerant Acetobacter malorum strains isolated from two biomes Moroccan cactus fruits

Abstract

Industrially, the sensitivity of acetic acid bacteria (AAB) to the high temperatures and the high ethanol concentrations is the major concerns for manufacturers. This study was conceived and designed to isolate and identify new thermo-and ethanol-tolerant AAB from Opuntia ficus-indica L. fruits. As a result, among 140 isolated bacterial strains, five selected strains (CR1, CR5, CR23, CZ2, and CZ15) exhibited important acetic acid production until 40°C. The use of 16S rDNA gene analysis was insufficient to identify selected bacteria. Indeed, except CR5 that presented 100% similarity to A. cerevisiae, the other strains presented similar homology rates simultaneously to the 16S rDNA sequences of A. cerevisiae and A. malorum. The reidentification by 16S-23S rDNA gene sequencing showed that CR1, CR23, and CZ15 were A. malorum, which were shown tolerance to the highest concentration of ethanol (12%) and produced elevated amount (40 g/L) of acetic acid at 37°C. In summary, we showed the thermotolerance and ethanol tolerant character of new A. malorum strains, which can be used as a starter for vinegar production. Furthermore, during the molecular characterization of the isolated strains, we concluded that 16S-23S rDNA internal transcribed spacer sequence is of great importance for discriminating between AAB species as a complement to the identification by 16S rDNA sequencing.

Influence of Different Bacteria Inocula and Temperature Levels on the Chemical Composition and Antioxidant Activity of Prickly Pear Vinegar Produced by Surface Culture

“…Contrariwise, at 37 • C none of these bacteria strains or combinations of strains produced high concentrations of acetic acid, so that the acetobacter strains, the gluconobacter strains and the mixed strains obtained from Sherry vinegar achieved similar concentrations of just 1.88, 1.90 and 1.89 g/100 mL, respectively. Several reasons could explain this lower productivity, such as the effect of the high temperature on the viability of the acetic acid bacteria even if the two genera displayed thermotolerant characteristics in a previous study [32]. Other reasons could be the greater evaporation of ethanol during the fermentation at the highest temperature or a poor tolerance to a large ethanol concentration in the wine (8.7%) when at a high temperature.…”

“…The experiments were conducted at 30 • C and 37 • C in duplicate and the flasks were not agitated to allow the atmospheric oxygen to diffuse slowly into the fermenting medium. A temperature of 37 • C showed the best results in terms of production of acetic acid by thermotolerant bacteria in a previous work [32] and it was compared with the usual acetification temperature (30 • C). The content in each flask was sampled every three weeks and each sample's total acidity was determined by titration with NaOH using phenolphthalein indicator.…”

“…Ten thermo-ethanol tolerant strains (5 Acetobacter and 5 Gluconobacter; AAB) were previously isolated from Moroccan prickly pear fruit following the procedure described in the previous work [32]. Further, a mixture of strains from an unfiltered Sherry vinegar (Jerez, Spain) was used in order to compare the different acetification profiles obtained from different bacteria inocula.…”

“…The acetic acid bacteria (AAB) strains that had presented thermo-ethanol tolerance characteristics in a previous study [32] were selected to be used as the starter culture for the acetic fermentation of the prickly pear wine at two different temperatures: 30 • C and 37 • C. The wine at 30 • C was fermented for 2 months, whereas the one at 37 • C was fermented for three months. The prickly pear vinegar produced by the surface culture at 30 • C reached a higher acidity value compared to that reached by the vinegar produced at 37 • C. This was probably due to the fact that at 30 • C all the bacteria from the Acetobacter genus had the capacity to produce acetic acid, which resulted in a mean value of 5.87 g/100 mL.…”

Two-Stage Polyhydroxyalkanoates (PHA) Production from Cheese Whey Using Acetobacter pasteurianus C1 and Bacillus sp. CYR1

“…Perumpuli et al reported that A. pasteurianus SL13E-2, SL13E-3, and SL13E-4 produced more than 40 g/L of acetic acid at 37 °C, an ethanol concentration of 46.58 g/L, and at 200 rpm [ 23 ]. Es-sbata et al reported that A. malorum strains produced more than 40 g/L of acetic acid at 37 °C [ 24 ]. Kadere et al isolated several Acetobacter and Gluconobacter strains.…”