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Appl Environ Microbiol, February 1998, p. 564-568, Vol. 64, No. 2
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Intracellular Signal Triggered by Cholera Toxin in Saccharomyces boulardii and Saccharomyces cerevisiae

Rogelio L. Brandão,1 Ieso M. Castro,1 Eduardo A. Bambirra,2 Sheila C. Amaral,1 Luciano G. Fietto,1 Maria José M. Tropia,1 Maria José Neves,3 Raquel G. Dos Santos,3 Newton C. M. Gomes,4 and Jacques R. Nicoli4,*

Laboratório de Fisologia e Bioquímica de Microorganismos, Escola de Farmácia, Universidade Federal de Ouro Preto, Ouro Preto,1 and Departamento de Anatomia Patológica, Faculdade de Medicina,2 Centro de Desenvolvimento de Tecnologia Nuclear,3 and Departamento de Microbiologia, Instituto de Ciências Biológicas,4 Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil

Received 20 February 1997/Accepted 13 November 1997

As is the case for Saccharomyces boulardii, Saccharomyces cerevisiae W303 protects Fisher rats against cholera toxin (CT). The addition of glucose or dinitrophenol to cells of S. boulardii grown on a nonfermentable carbon source activated trehalase in a manner similar to that observed for S. cerevisiae. The addition of CT to the same cells also resulted in trehalase activation. Experiments performed separately on the A and B subunits of CT showed that both are necessary for activation. Similarly, the addition of CT but not of its separate subunits led to a cyclic AMP (cAMP) signal in both S. boulardii and S. cerevisiae. These data suggest that trehalase stimulation by CT probably occurred through the cAMP-mediated protein phosphorylation cascade. The requirement of CT subunit B for both the cAMP signal and trehalase activation indicates the presence of a specific receptor on the yeasts able to bind to the toxin, a situation similar to that observed for mammalian cells. This hypothesis was reinforced by experiments with 125I-labeled CT showing specific binding of the toxin to yeast cells. The adhesion of CT to a receptor on the yeast surface through the B subunit and internalization of the A subunit (necessary for the cAMP signal and trehalase activation) could be one more mechanism explaining protection against the toxin observed for rats treated with yeasts.

* Corresponding author. Mailing address: Departmento de Microbiologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, C.P. 428, 30161-970 Belo Horizonte, MG, Brazil. Phone: 55 31 499 27 57. Fax: 55 31 441 59 63. E-mail: jnicoli{at}mono.icb.ufmg.br.




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Copyright © 1998 by the American Society for Microbiology. All rights reserved.