Sousa Maria João, Rodrigues Fernando, Coôrte-Real Manuela, Leão Cecília
Microbiology (Reading). 1998 Mar;144 ( Pt 3):665-670. doi: 10.1099/00221287-144-3-665.
Zygosaccharomyces bailii ISA 1307 displays biphasic growth in a medium containing a mixture of glucose (0.5%, w/v) and acetic acid (0.5%, w/v), pH 5.0 and 3.0. In cells harvested during the first growth phase, no activity of a mediated acetic acid transport system was found. Incubation of these cells in phosphate buffer with cycloheximide for 1 h restored activity of an acetic acid carrier which behaved as the one present in glucose-grown cells. These results indicated that the acetic acid carrier is probably present in cells from the first growth phase of the mixed medium but its activity was affected by the presence of acetic acid in the culture medium. In glucose-grown cells, after incubation in phosphate buffer with glucose and acetic acid, the activity of the acetic acid carrier decreased significantly with increased acid concentration in the incubation buffer. At acid concentrations above 16.7 mM, no significant carrier activity was detectable. Furthermore, the intracellular acid concentration increased with the extracellular one and was inversely correlated with the activity of the acetic acid carrier, suggesting the involvement of a feedback inhibition mechanism in the regulation of the carrier. During biphasic growth, the first phase corresponded to a simultaneous consumption of glucose and acetic acid, and the second to the utilization of the remaining acid. The enzyme acetyl-CoA synthetase was active in both growth phases, even in the presence of glucose. Activity of isocitrate lyase and phosphoenolpyruvate carboxykinase was found only in acetic-acid-grown cells. Thus it appears that both membrane transport and acetyl-CoA synthetase and their regulation are important for Z. bailii to metabolize acetic acid in the presence of glucose. This fact correlates with the high resistance of this yeast to environments with mixtures of sugars and acetic acid such as those often present during wine fermentation.
拜耳接合酵母ISA 1307在含有葡萄糖（0.5%，w/v）和乙酸（0.5%，w/v）的混合培养基（pH 5.0和3.0）中呈现双相生长。在第一个生长阶段收获的细胞中，未发现介导的乙酸转运系统的活性。将这些细胞在含有环己酰亚胺的磷酸盐缓冲液中孵育1小时后，乙酸载体的活性恢复，其表现与在葡萄糖培养的细胞中存在的载体相同。这些结果表明，乙酸载体可能存在于混合培养基第一个生长阶段的细胞中，但其活性受到培养基中乙酸存在的影响。在葡萄糖培养的细胞中，在含有葡萄糖和乙酸的磷酸盐缓冲液中孵育后，乙酸载体的活性随着孵育缓冲液中酸浓度的增加而显著降低。在酸浓度高于16.7 mM时，未检测到明显的载体活性。此外，细胞内酸浓度随着细胞外酸浓度增加而增加，并且与乙酸载体的活性呈负相关，这表明反馈抑制机制参与了载体的调节。在双相生长期间，第一阶段对应于葡萄糖和乙酸的同时消耗，第二阶段对应于剩余酸的利用。乙酰辅酶A合成酶在两个生长阶段均有活性，即使在有葡萄糖存在的情况下也是如此。异柠檬酸裂解酶和磷酸烯醇式丙酮酸羧激酶仅在乙酸培养的细胞中被发现。因此，膜转运以及乙酰辅酶A合成酶及其调节对于拜耳接合酵母在葡萄糖存在下代谢乙酸似乎都很重要。这一事实与这种酵母对糖和乙酸混合物环境（如葡萄酒发酵过程中经常出现的环境）的高抗性相关。
