El-Askri Taoufik, Yatim Meriem, Sehli Youness, Rahou Abdelilah, Belhaj Abdelhaq, Castro Remedios, Durán-Guerrero Enrique, Hafidi Majida, Zouhair Rachid
Laboratory of Plant Biotechnology and Bio-Resources Valorization, Department of Biology, Faculty of Sciences, Moulay Ismail University, Zitoune, Meknes 50050, Morocco.
Analytical Chemistry Department, Faculty of Sciences-IVAGRO, Agrifood Campus of International Excellence (CeiA3), University of Cadiz, Polígono Río San Pedro, s/n, 11510 Cadiz, Spain.
Microorganisms. 2022 Aug 29;10(9):1741. doi: 10.3390/microorganisms10091741.
The production of vinegar on an industrial scale from different raw materials is subject to constraints, notably the low tolerance of acetic acid bacteria (AAB) to high temperatures and high ethanol concentrations. In this study, we used 25 samples of different fruits from seven Moroccan biotopes with arid and semi-arid environmental conditions as a basic substrate to isolate thermo- and ethanol-tolerant AAB strains. The isolation and morphological, biochemical and metabolic characterization of these bacteria allowed us to isolate a total number of 400 strains with characters similar to AAB, of which six strains (FAGD1, FAGD10, FAGD18 and GCM2, GCM4, GCM15) were found to be mobile and immobile Gram-negative bacteria with ellipsoidal rod-shaped colonies that clustered in pairs and in isolated chains. These strains are capable of producing acetic acid from ethanol, growing on peptone and oxidizing acetate to CO2 and H2O. Strains FAGD1, FAGD10 and FAGD18 show negative growth on YPG medium containing D-glucose > 30%, while strains GCM2, GCM4 and GCM15 show positive growth. These six strains stand out on CARR indicator medium as isolates of the genus Acetobacter ssp. Analysis of 16S rDNA gene sequencing allowed us to differentiate these strains as Acetobacter fabarum and Acetobacter pasteurianus. The study of the tolerance of these six isolates towards pH showed that most of the six strains are unable to grow at pH 3 and pH 9, with an ideal pH of 5. The behavior of the six strains at different concentrations of ethanol shows an optimal production of acetic acid after incubation at concentrations between 6% and 8% (v/v) of ethanol. All six strains tolerated an ethanol concentration of 16% (v/v). The resistance of the strains to acetic acid differs between the species of AAB. The optimum acetic acid production is obtained at a concentration of 1% (v/v) for the strains of FAGD1, FAGD10 and FAGD18, and 3% (v/v) for GCM2, GCM4 and GCM15. These strains are able to tolerate an acetic acid concentration of up to 6% (v/v). The production kinetics of the six strains show the highest levels of growth and acetic acid production at 30 °C. This rate of growth and acetic acid production is high at 35 °C, 37 °C and 40 °C. Above 40 °C, the production of acid is reduced. All six strains continue to produce acetic acid, even at high temperatures up to 48 °C. These strains can be used in the vinegar production industry to minimize the load on cooling systems, especially in countries with high summer temperatures.
以不同原材料进行工业规模的醋生产受到诸多限制，尤其是醋酸菌（AAB）对高温和高乙醇浓度的耐受性较低。在本研究中，我们使用了来自摩洛哥七个具有干旱和半干旱环境条件的生物群落的25种不同水果样本作为基础底物，以分离耐热和耐乙醇的AAB菌株。对这些细菌的分离以及形态、生化和代谢特征分析使我们总共分离出400株具有与AAB相似特征的菌株，其中六株（FAGD1、FAGD10、FAGD18和GCM2、GCM4、GCM15）被发现是可运动和不可运动的革兰氏阴性菌，具有椭圆形杆状菌落，成对聚集并形成孤立的链状。这些菌株能够从乙醇中产生乙酸，在蛋白胨上生长，并将乙酸氧化为二氧化碳和水。菌株FAGD1、FAGD10和FAGD18在含有>30% D - 葡萄糖的YPG培养基上生长呈阴性，而菌株GCM2、GCM4和GCM15生长呈阳性。这六株菌株在CARR指示培养基上作为醋酸杆菌属的分离株脱颖而出。对16S rDNA基因测序的分析使我们能够将这些菌株鉴定为巴氏醋酸杆菌和法氏醋酸杆菌。对这六株分离株的pH耐受性研究表明，这六株菌株中的大多数在pH 3和pH 9时无法生长，理想pH为5。这六株菌株在不同乙醇浓度下的行为表明，在6%至8%（v/v）的乙醇浓度下孵育后，乙酸产量达到最佳。所有六株菌株都能耐受16%（v/v）的乙醇浓度。不同种类的AAB菌株对乙酸的抗性有所不同。FAGD1、FAGD10和FAGD18菌株在1%（v/v）的乙酸浓度下获得最佳乙酸产量，而GCM2、GCM4和GCM15菌株在3%（v/v）时获得最佳产量。这些菌株能够耐受高达6%（v/v）的乙酸浓度。这六株菌株的生产动力学表明，在30°C时生长和乙酸产量水平最高。在35°C、37°C和40°C时，这种生长和乙酸产量速率也较高。高于40°C，酸产量会降低。即使在高达48°C的高温下，所有六株菌株仍继续产生乙酸。这些菌株可用于醋生产行业，以减少冷却系统的负荷，特别是在夏季温度较高的国家。
