Review: Adaptation of Beneficial Propionibacteria, Lactobacilli, and Bifidobacteria Improves Tolerance Toward Technological and Digestive Stresses

Abstract

This review deals with beneficial bacteria, with a focus on lactobacilli, propionibacteria, and bifidobacteria. As being recognized as beneficial bacteria, they are consumed as probiotics in various food products. Some may also be used as starters in food fermentation. In either case, these bacteria may be exposed to various environmental stresses during industrial production steps, including drying and storage, and during the digestion process. In accordance with their adaptation to harsh environmental conditions, they possess adaptation mechanisms, which can be induced by pretreatments. Adaptive mechanisms include accumulation of compatible solutes and of energy storage compounds, which can be largely modulated by the culture conditions. They also include the regulation of energy production pathways, as well as the modulation of the cell envelop, i.e., membrane, cell wall, surface layers, and exopolysaccharides. They finally lead to the overexpression of molecular chaperones and of stress-responsive proteases. Triggering these adaptive mechanisms can improve the resistance of beneficial bacteria toward technological and digestive stresses. This opens new perspectives for the improvement of industrial processes efficiency with regard to the survival of beneficial bacteria. However, this bibliographical survey evidenced that adaptive responses are strain-dependent, so that growth and adaptation should be optimized case-by-case.

Keywords: adaptation; drying; osmo regulation; probiotic; stress.

FIGURE 1

Key actors of adaptive mechanisms in bacteria during osmotic, acid, oxidative, heat, cold, and bile salts adaptation. General adaptive bacterial mechanisms during osmotic, acid, oxidative, heat, cold, and bile salts treatment are represented. Peptidoglycan is represented in blue. Membrane lipids under normal growth are represented in gray. Amounts of saturated (blue), unsaturated (red), and cyclic (yellow) fatty acids are modulated by treatments. S-layer proteins, which may be involved in adaptation, are represented in yellow and red outside the peptidoglycan. Liptechoic acids, whose length is modulated, are presented in green. Inducible transmembrane ATPase and osmoprotectant uptake systems are represented in pink and blue, respectively. In the cytoplasm, general stress proteins are represented by different colors. Colored circles represent different osmoprotectant and energy storage compounds. Crosses on circles mean the conversion of the molecule. The chromosome is represented in black. The numbers indicate corresponding references in the tables.

FIGURE 2

Different treatments modulate the key actors of adaptive mechanisms. Colored areas represent the different treatments studied. In yellow: oxidative; in red: heat; in green: acid; in brown: bile salts; in blue: cold; and in purple: osmotic treatment. The key actors of adaptive mechanisms indicated inside a bubble are modulated by the corresponding treatment. The numbers indicate corresponding references in the tables.

FIGURE 3

Stressing pretreatments and modifications of the growth medium modulate survival during technological and digestive stresses. Technological and digestive stresses are represented in the figure. Digestion triggers two main stresses: bile salts and acid stress. For each stress, the impact of stressing pretreatments and of modifications of the growth medium on bacteria survival is indicated (+: positive; -: negative; and 0: no effect). Strain-dependent modulations are represented by arrows (purple: osmotic; blue: cold; red: heat; yellow: oxidative; green: acid; brown: bile salts treatment). Large arrows indicate a positive effect and thin arrows indicate either no effect or a negative effect. The numbers indicate corresponding references in the tables.