CARME PLUMED-FERRER Lactobacillus plantarum From Application to Protein Expression

Lactic acid bacteria (LAB) are a heterogeneous group of organisms found in a wide range of environmental niches due to their large adaptation capacity. They are responsible for the fermentation of many fermented food and feed products because they can transform sugars into organic acids and decrease the pH of the medium. This acidification prevents the growth of pathogenic bacteria, making the fermented product safe for the consumer. However, a product that has been fermented spontaneously has the disadvantage of being unpredictable and uncontrollable. A solution to this problem is inoculation with a concentrated bacterial culture (starter culture) in order to control the fermentation process. Liquid feeding is a common system in Finland for feeding pigs of all ages. Although feeding pigs with a liquid diet is not a new technique, much recent research has focused on explaining the benefits because it can replace the use of antibiotics in animal production. However, pig liquid feed is rapidly spoiled by pathogens such as Enterobacteriaceae unless the lactic acid bacteria population dominates the fermentation. In order to solve this problem, we looked for a lactic acid bacterium that could control the fermentation in this particular matrix. For this purpose, the stability of the liquid feed was analysed and the lactic acid bacterial population identified. A Lactobacillus plantarum strain was chosen as a potential starter culture for this type of feed. Subsequently, two trials were conducted in order to check the growth potential of this bacterium in liquid feed prepared in laboratory conditions and later in a commercial farm with the purpose of obtaining real life results. The results suggested that Lactobacillus plantarum REB1 had the potential to be used as starter culture in pig liquid feed, providing a proper fermentation with high numbers of lactic acid bacteria, low pH, stable numbers of yeasts and low Enterobacteriaceae. Moreover, the extensive adaptation capacity of Lactobacillus plantarum and the wide range of applications where this bacterium has been used makes research on this topic especially interesting and challenging. For this reason, two strains of Lactobacillus plantarum from different origin (REB1 and MLBPL1, the latter from vegetable material) were used in proteomics studies in order to check metabolic differences between strains and between growth conditions. The results show that the metabolisms of both strains are very similar. They were found to ferment different carbohydrates simultaneously (hexoses and pentoses) with preferential expression in the early-exponential phase, and to use carbohydrates differently in three media even though there was always an excess of glucose content. Overall, this study has identified a bacterial strain with potential applications, and provided a better understanding of the metabolic capacity of this particular species and some clues about their adaptation potential. Universal Decimal Classification: 579.864, 636.084. 422, 636.4, 577.124 National Library of Medicine Classification: QW 85, QW 142.5. A8, QU 34 CAB Thesaurus: lactic acid bacteria; Lactobacillus plantarum; pigs; pig feeding; wet feeding; fermentation; starters; carbohydrate metabolism; bacterial proteins; electrophoresis; mass spectrometry.