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Applied and Environmental Microbiology, April 2008, p. 2370-2378, Vol. 74, No. 8
0099-2240/08/$08.00+0     doi:10.1128/AEM.02737-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Role of Ureolytic Activity in Bacillus cereus Nitrogen Metabolism and Acid Survival{triangledown}

Maarten Mols1,2 and Tjakko Abee1,2*

Top Institute Food and Nutrition, Wageningen, The Netherlands,1 Laboratory of Food Microbiology, Wageningen University, Wageningen, The Netherlands2

Received 5 December 2007/ Accepted 11 February 2008

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.

* Corresponding author. Mailing address: Laboratory of Food Microbiology, Wageningen University, Bomenweg 2, 6703 HD Wageningen, The Netherlands. Phone: 31-317-484981. Fax: 31-317-484978. E-mail: tjakko.abee{at}wur.nl

{triangledown} Published ahead of print on 22 February 2008.

Applied and Environmental Microbiology, April 2008, p. 2370-2378, Vol. 74, No. 8
0099-2240/08/$08.00+0     doi:10.1128/AEM.02737-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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