Oenococcus oeni shows several genomic peculiarities, e.g. it has the smallest known genome for a lactic acid bacterium, and it lacks the mismatch repair (MMR) system. In particular, the defective MMR system is probably responsible for its great intra-specific variability, linked to an increase of the mutation frequency, as well as of the horizontal gene transfer among strains (Marcobal et al., 2008). A distinctive physiological feature of O. oeni is its ability to grow in wine and perform the malolactic fermentation (MLF), which is required to improve the organolectic quality of certain styles of wines. Oenococcus oeni is therefore a very interesting species for its adaptation to an unique and hostile ecological niche characterized by acidic pH, high ethanol content and other stress factors. The aim of the present study was to investigate the stress response in O. oeni in terms of distribution of selected genes in several strains and their gene expression in different conditions in the reference bacterium PSU-1 (Mills et al., 2005). A collection of 14 O. oeni strains with different oenological characteristics was screened for the presence of the stress resistance markers described by Renouf et al. (2008). A remarkable variability among them was observed, showing that proposed genetic traits are strain-specific and that are not associated with the ability to grow and complete MLF in wine. As the highest number of markers was shown by PSU-1, a gene expression experiment was conducted on this strain to analyse changes under different stress conditions, such as exposition to low pH (3.5), presence of ethanol (10% v/v), both conditions simultaneously, and heat shock at 42°C for 6 hours. PSU-1 expression data revealed that about half of the targeted genes were differentially expressed among the tested conditions, confirming their involvement in stress response. The findings of the present study underline the great diversity of the genetic makeup related to stress response in different strains. This confirms that adaptability to the specific niche is most probably due to the lack of MMR system. Considering the scarce phylogenetic relatedness of O. oeni with Bacillus subtilis and Lactococcus lactis, its genomic peculiarities and its applied importance, we believe that it could be considered an additional and useful model microorganism for the study of stress response in low GC Gram-positive bacteria.
Stress response in Oenococcus oeni: intra-specific diversity and gene expression
STEFANELLI, ELENA;FELIS, Giovanna;TORRIANI, Sandra;FRACCHETTI, Fabio
2011-01-01
Abstract
Oenococcus oeni shows several genomic peculiarities, e.g. it has the smallest known genome for a lactic acid bacterium, and it lacks the mismatch repair (MMR) system. In particular, the defective MMR system is probably responsible for its great intra-specific variability, linked to an increase of the mutation frequency, as well as of the horizontal gene transfer among strains (Marcobal et al., 2008). A distinctive physiological feature of O. oeni is its ability to grow in wine and perform the malolactic fermentation (MLF), which is required to improve the organolectic quality of certain styles of wines. Oenococcus oeni is therefore a very interesting species for its adaptation to an unique and hostile ecological niche characterized by acidic pH, high ethanol content and other stress factors. The aim of the present study was to investigate the stress response in O. oeni in terms of distribution of selected genes in several strains and their gene expression in different conditions in the reference bacterium PSU-1 (Mills et al., 2005). A collection of 14 O. oeni strains with different oenological characteristics was screened for the presence of the stress resistance markers described by Renouf et al. (2008). A remarkable variability among them was observed, showing that proposed genetic traits are strain-specific and that are not associated with the ability to grow and complete MLF in wine. As the highest number of markers was shown by PSU-1, a gene expression experiment was conducted on this strain to analyse changes under different stress conditions, such as exposition to low pH (3.5), presence of ethanol (10% v/v), both conditions simultaneously, and heat shock at 42°C for 6 hours. PSU-1 expression data revealed that about half of the targeted genes were differentially expressed among the tested conditions, confirming their involvement in stress response. The findings of the present study underline the great diversity of the genetic makeup related to stress response in different strains. This confirms that adaptability to the specific niche is most probably due to the lack of MMR system. Considering the scarce phylogenetic relatedness of O. oeni with Bacillus subtilis and Lactococcus lactis, its genomic peculiarities and its applied importance, we believe that it could be considered an additional and useful model microorganism for the study of stress response in low GC Gram-positive bacteria.
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