Dipartimento di Scienze e Tecnologie Alimentari e Microbiologiche, Università degli Studi di Milano, Milan, Italy.
PLoS One. 2010 Nov 30;5(11):e15520. doi: 10.1371/journal.pone.0015520.
An understanding of the integrated relationships among the principal cellular functions that govern the bioenergetic reactions of an organism is necessary to determine how cells remain viable and optimise their fitness in the environment. Urease is a complex enzyme that catalyzes the hydrolysis of urea to ammonia and carbonic acid. While the induction of urease activity by several microorganisms has been predominantly considered a stress-response that is initiated to generate a nitrogen source in response to a low environmental pH, here we demonstrate a new role of urease in the optimisation of cellular bioenergetics. We show that urea hydrolysis increases the catabolic efficiency of Streptococcus thermophilus, a lactic acid bacterium that is widely used in the industrial manufacture of dairy products. By modulating the intracellular pH and thereby increasing the activity of β-galactosidase, glycolytic enzymes and lactate dehydrogenase, urease increases the overall change in enthalpy generated by the bioenergetic reactions. A cooperative altruistic behaviour of urease-positive microorganisms on the urease-negative microorganisms within the same environment was also observed. The physiological role of a single enzymatic activity demonstrates a novel and unexpected view of the non-transcriptional regulatory mechanisms that govern the bioenergetics of a bacterial cell, highlighting a new role for cytosol-alkalizing biochemical pathways in acidogenic microorganisms.
理解控制生物体生物能量反应的主要细胞功能的综合关系对于确定细胞如何保持活力并在环境中优化其适应性是必要的。脲酶是一种复杂的酶，它催化尿素水解为氨和碳酸。虽然几种微生物诱导脲酶活性主要被认为是一种应激反应，是为了在环境 pH 值较低时产生氮源而启动的，但在这里，我们展示了脲酶在优化细胞生物能量学方面的新作用。我们表明，尿素水解提高了嗜热链球菌的分解代谢效率，嗜热链球菌是一种广泛用于乳制品工业生产的乳酸细菌。通过调节细胞内 pH 值，从而增加β-半乳糖苷酶、糖酵解酶和乳酸脱氢酶的活性，脲酶增加了生物能量反应产生的总焓变。还观察到同一环境中脲酶阳性微生物对脲酶阴性微生物的协同利他行为。单一酶活性的生理作用展示了一种新的、意想不到的非转录调控机制，该机制控制着细菌细胞的生物能量学，突出了胞质碱化生化途径在产酸微生物中的新作用。
