Abstract
Liquorilactobacillus (L.) hordei (formerly Lactobacillus hordei) is one of the dominating lactic acid bacteria within the water kefir consortium, being highly adapted to survive in this environment, while producing high molecular weight dextrans from sucrose. In this work, we extensively studied the physiological response of L. hordei TMW 1.1822 to sucrose compared to glucose, applying label-free, quantitative proteomics of cell lysates and exoproteomes. This revealed the differential expression of 53 proteins within cellular proteomes, mostly associated with carbohydrate uptake and metabolism. Supported by growth experiments, this suggests that L. hordei TMW 1.1822 favors fructose over other sugars. The dextransucrase was expressed irrespectively of the present carbon source, while it was significantly more released in the presence of sucrose (log2FC = 3.09), being among the most abundant proteins within exoproteomes of sucrose-treated cells. Still, L. hordei TMW 1.1822 expressed other sucrose active enzymes, predictively competing with the dextransucrase reaction. While osmolysis appeared to be unlikely, sucrose led to increased release of a multitude of cytoplasmic proteins, suggesting that biofilm formation in L. hordei is not only composed of a polysaccharide matrix but is also of proteinaceous nature. Therefore, our study highlights the intrinsic adaptation of water kefir-borne L. hordei to sucrose-rich habitats and provides fundamental knowledge for its use as a starter culture in plant-based food fermentations with in situ dextran formation.
Highlights
In the food sector, the new health conscious nature of the western population nowadays demands innovative approaches in the production of foods with sophisticated nutritional and techno-functional properties [1,2]
As the majority of proteins identified in the exoproteome of both conditions belonged to cytoplasmic proteins, we examined the quantitative correlation of the exoproteomes and the cellular proteomes in order to identify proteins that are significantly more concentrated in the exoproteome and most likely proteins that were actively secreted
L. hordei TMW 1.1822 in response to sucrose by the analysis of cellular and extracellular proteomes as well as physiological tests
Summary
In the food sector, the new health conscious nature of the western population nowadays demands innovative approaches in the production of foods with sophisticated nutritional and techno-functional properties [1,2]. Fermented fruit and vegetable products already have a long history and are only waiting to be explored for the occurrence of microorganisms that may be exploited in innovative food manufacturing processes. Water kefir is a traditional fermented beverage that is made from dried fruits, lemon slices and sucrose, and its microbiota is perfectly adapted to metabolize plant-derived. The kefir granules, which harbor a complex consortium of mainly yeasts, lactic acid bacteria (LAB), acetic acid bacteria and bifidobacteria, host an interesting reservoir for microorganisms, which can be applied in innovative plant-based food and beverage fermentations [12]. While some water kefir-borne LAB were already shown to exhibit probiotic potential [13,14], the production of exopolysaccharides with different techno-functional properties harbors additional application potential [15,16]. Dextrans are mainly α-1,6-linked glucans that are formed from sucrose by extracellular enzymes, namely dextransucrases [18,19]
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