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P Piper

Publications and source records attributed to P Piper.

17 recordsLinked to original sources
PubMed2001

Targeted gene deletion in Zygosaccharomyces bailii.

Yeasts of the genus Zygosaccharomyces are notable agents of large-scale food spoilage. Despite the economic importance of these organisms, little is known about the stress adaptations whereby they adapt to many of the more severe conditions of food preservation. In this study it was shown that genes of Z. bailii, a yeast notable for its high resistances to food preservatives and ethanol, can be isolated by complementation of the corresponding mutant strains of Saccharomyces cerevisiae. It was also discovered that the acquisition by S. cerevisiae of a single small Z. bailii gene (ZbYME2) was sufficient for the former yeast to acquire the ability to degrade two major food preservatives, benzoic acid and sorbic acid. Using DNA cassettes containing dominant selectable markers and methods originally developed for performing gene deletions in S. cerevisiae, the two copies of ZbYME2 in the Z. bailii genome were sequentially deleted. The resulting Zbyme2/Zbyme2 homozygous deletant strain had lost any ability to utilize benzoate as sole carbon source and was more sensitive to weak acid preservatives during growth on glucose. Thus, ZbYME2, probably the nuclear gene for a mitochondrial mono-oxygenase function, is essential for Z. bailii to degrade food preservatives. This ability to catabolize weak acid preservatives is a significant factor contributing to the preservative resistance of Z. bailii under aerobic conditions. This study is the first to demonstrate that it is possible to delete in Z. bailii genes that are suspected as being important for growth of this organism in preserved foods and beverages. With the construction of further mutant of Z. bailii strains, a clearer picture should emerge of how this yeast adapts to the conditions of food preservation. This information will, in turn, allow the design of new preservation strategies. GenBank Accession Nos: ZbURA3 (AF279259), ZbTIM9 (AF279260), ZbYME2 (AF279261), ZbTRP1 (AF279262), ZbHHT1(AF296170).

Acids↗
PubMed1998

The pdr12 ABC transporter is required for the development of weak organic acid resistance in yeast.

Exposure of Saccharomyces cerevisiae to sorbic acid strongly induces two plasma membrane proteins, one of which is identified in this study as the ATP-binding cassette (ABC) transporter Pdr12. In the absence of weak acid stress, yeast cells grown at pH 7.0 express extremely low Pdr12 levels. However, sorbate treatment causes a dramatic induction of Pdr12 in the plasma membrane. Pdr12 is essential for the adaptation of yeast to growth under weak acid stress, since Deltapdr12 mutants are hypersensitive at low pH to the food preservatives sorbic, benzoic and propionic acids, as well as high acetate levels. Moreover, active benzoate efflux is severely impaired in Deltapdr12 cells. Hence, Pdr12 confers weak acid resistance by mediating energy-dependent extrusion of water-soluble carboxylate anions. The normal physiological function of Pdr12 is perhaps to protect against the potential toxicity of weak organic acids secreted by competitor organisms, acids that will accumulate to inhibitory levels in cells at low pH. This is the first demonstration that regulated expression of a eukaryotic ABC transporter mediates weak organic acid resistance development, the cause of widespread food spoilage by yeasts. The data also have important biotechnological implications, as they suggest that the inhibition of this transporter could be a strategy for preventing food spoilage.

ATP-Binding Cassette Transporters↗
PubMed1996

Over-expression of Saccharomyces cerevisiae hsp90 enhances the virulence of this yeast in mice.

Saccharomyces cerevisiae, a yeast of low pathogenic potential, is a rare but well-documented cause of invasive infections in humans. The yeast Candida albicans is a much commoner cause of significant and life-threatening infections. In such infections the heat shock protein hsp90 is an immunodominant antigen associated with protective humoral immunity. In this study it was shown that over-expression of S. cerevisiae hsp90, the amino acid sequence of which shows 84% identity to C. albicans hsp90, significantly increased the virulence of a laboratory strain of S. cerevisiae in mice, both in terms of colony counts in the kidney, liver, and spleen, and in terms of mortality. This is the first direct evidence that hsp90 is a virulence factor.

Animals↗
PubMed1996

The molecular defences against reactive oxygen species in yeast.

There is rapidly expanding interest into the protective systems against reactive oxygen species (ROS) in the eukaryotic cell, now that the links between oxidative damage, various disease states, and ageing, are firmly established in higher organisms. Yeast molecular genetics should be able to provide powerful insight into these mechanisms; this potential is now starting to be exploited. A number of primary antioxidant activities and systems of metal-ion homeostasis or detoxification have now been demonstrated to contribute to oxidative-stress protection in yeast. Also, evidence is emerging that the oxidative-stress response of this organism is complex, involving separate transcription-factor responses to peroxide, superoxide anion and metal ions.

Oxidative Stress↗
PubMed1991

Acquisition of thermotolerance in Saccharomyces cerevisiae without heat shock protein hsp 104 and in the absence of protein synthesis.

Acquisition of thermotolerance in response to a preconditioning heat treatment at 40 degrees C was studied in mutants of the yeast Saccharomyces cerevisiae lacking a specific heat shock protein or the ability to synthesize proteins at 40 degrees C. A mutant carrying a deletion of heat shock protein hsp 104 and the corresponding wildtype strain were both highly sensitive to heat stress at 50.4 degrees C without preconditioning but both acquired almost the same level of thermotolerance after 60 min of preconditioning. Both strains showed equal induction of trehalose-6-phosphate synthase and accumulated equal levels of trehalose during the treatment. The conditional mutant ts--187 synthesized no proteins during the preconditioning heat treatment but nevertheless acquired thermotolerance, albeit to a lesser degree than the corresponding wildtype strain. Induction of trehalose-6-phosphate synthase and accumulation of trehalose were reduced to a similar extent. These results show that acquisition of thermotolerance and accumulation of trehalose are closely correlated during heat preconditioning and are modulated by protein synthesis but do not require it.

Adaptation, Physiological↗
PubMed1979

Splicing of the late mRNAs of polyoma virus does not occur in the cytoplasm of the infected cell.

The three mRNAs that encode the capsid proteins of polyoma virus are produced by the excision of different sequences from continuous transcripts of the L strand of viral DNA. All three of the mRNAs have long half lives, and the larger species are not converted to the smaller ones to any measurable extent within the cytoplasm. Therefore the cytoplasmic proportions of late polyoma mRNAs are predetermined by splicing that is confined to the nucleus of the infected cell and which is complete by the time that mRNA is transported to the cytoplasm.

Animals↗