Mols Maarten, Abee Tjakko
Laboratory of Food Microbiology, Wageningen University, Bomenweg 2, 6703 HD Wageningen, The Netherlands.
Appl Environ Microbiol. 2008 Apr;74(8):2370-8. doi: 10.1128/AEM.02737-07. Epub 2008 Feb 22.
The presence and activities of urease genes were investigated in 49 clinical, food, and environmental Bacillus cereus isolates. Ten strains were shown to have urease genes, with eight of these strains showing growth on urea as the sole nitrogen source. Two of the urease-positive strains, including the sequenced strain ATCC 10987, could not use urea for growth, despite their capacities to produce active urease. These observations can be explained by the inability of the two strains to use ammonium as a nitrogen source. The impact of urea hydrolysis on acid stress resistance was subsequently assessed among the ureolytic B. cereus strains. However, none of the strains displayed increased fitness under acidic conditions or showed enhanced acid shock survival in the presence of urea. Expression analysis of urease genes in B. cereus ATCC 10987 revealed a low level of expression of these genes and a lack of pH-, nitrogen-, urea-, oxygen-, and growth phase-dependent modulation of mRNA transcription. This is in agreement with the low urease activity observed in strain ATCC 10987 and the other nine strains tested. Although a role for B. cereus ureolytic activity in acid survival cannot be excluded, its main role appears to be in nitrogen metabolism, where ammonium may be provided to the cells in nitrogen-limited, urea-containing environments.
对49株临床、食品和环境来源的蜡样芽孢杆菌分离株的脲酶基因存在情况及其活性进行了研究。结果显示，有10株菌株含有脲酶基因，其中8株菌株能够以尿素作为唯一氮源生长。包括已测序的ATCC 10987菌株在内的2株脲酶阳性菌株，尽管能够产生活性脲酶，但却无法利用尿素进行生长。这一现象可以通过这两株菌株无法利用铵作为氮源来解释。随后评估了尿素水解对产脲酶蜡样芽孢杆菌菌株耐酸胁迫能力的影响。然而，在酸性条件下，这些菌株均未表现出适应性增强，在有尿素存在的情况下也未表现出酸休克存活率提高。蜡样芽孢杆菌ATCC 10987中脲酶基因的表达分析显示，这些基因的表达水平较低，且mRNA转录缺乏pH、氮、尿素、氧和生长阶段依赖性调节。这与在ATCC 10987菌株和其他9株受试菌株中观察到的低脲酶活性一致。虽然不能排除蜡样芽孢杆菌的脲解活性在耐酸生存中的作用，但其主要作用似乎在于氮代谢，即在氮受限的含尿素环境中为细胞提供铵。
