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Stress response of bifidobacteria

Bifidobacteria are among the first species to colonise the human gastrointestinal tract and as such are believed to play an important role in gut homeostasis and normal development. Nowadays, bifidobacteria have become economically important since they are added in high numbers as live bacteria in numerous food preparations with various health-related claims. These bacteria are not naturally found in food but are purposely added to it as live bacteria because of their claimed health benefits. Examples of such products include infant formulas, cheese, dietary supplements and fermented dairy products. However, survival of bifidobacteria in food products remains sometimes problematic. In consequence, active research is needed to gain an insight into the different factors that may impact on bacterial survival and resistance to stress.

In the past few years the complete genome sequence of a number of bacterial strains isolated from the human gastrointestinal tract has been established, including that of a specific B. longum strain isolated from the faeces of a healthy infant. Knowledge of this genome sequence allowed the design of DNA based arrays, containing a set of B. longum genes. These DNA arrays were used for global expression profiling in response to environmental changes. By compiling expression profiles from a range of different environmental stresses it was possible to identify genes that are commonly induced in response to these unfavourable conditions. The proteins encoded by these genes are thought to provide non-specific protection to the cell in the event of adverse conditions, whereas additional genes can be transcribed in response to a specific type of stress.

To learn more about the general stress responses of B. longum NCC2705, expression profiles obtained after three different stresses namely, oxidative stress, starvation and heat shock were compiled. In all cases, cells were grown under identical controlled conditions and subjected to either a heat shock, exposure to H2O2 or transition into stationary phase. The gene expression profiles observed in response to these stresses were compared to those obtained from exponentially growing cells. Twenty-one genes were identified as being induced by a factor greater than 2.5-fold including genes such as dnaK, grpE, dnaJ, hspR, groEL, groES, clpB, hrcA. Also of interest are several upregulated genes encoding proteins with no predicted function that could possibly play a general role in protecting B. longum cells from unfavourable conditions. Noteworthy, we identified a gene rapidly and highly induced under different conditions that may be developed as a stress marker. Stress markers can be used to monitor the physiological status of the cells or help to identify experimental parameters that will lead to high induction of the general stress response.

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Nestec S.A. (NESTEC)
Vers-Chez-Les-Blanc 1000
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