Diversity of lactic acid bacteria from wild fruits and flowers of Northern Argentina. Production of Mannitol and seleno-amino acids

F. MOZZI

Congreso; V Microbial Diversity Congress; 2019

SIMTREA, ICFMH, FEMS

Lactic acid bacteria (LAB) constitute a large group of microorganisms that inhabit a plethora of niches of dairy (fermented), meat and vegetable origin, the gastrointestinal and urogenital tracts of humans and animals, and soil and water. Tropical fruits and flowers present in Northern Argentina are an interesting source of a variety of LAB including fructophilic bacteria. The fructose-rich content of fruits and flowers along with visiting insects, pollinators, and environmental factors, shape the microbial community of this niche. Twenty-one LAB species belonging to six different genera namely Enterococcus, Fructobacillus, Lactobacillus, Lactococcus, Leuconostoc and Weissella were isolated from the flowers and the ripe wild fruits of guava, papaya, passion fruit, custard apple, medlar, mulberry, fig, and khaki. The largest cluster of isolates (155) belonged to Leuc. pseudomesenteroides, which were widely distributed among the samples assayed while the second largest group was formed by 140 fingerprints identified as F. tropaeoli; this species being only found in custard apple, fig, and khaki. Isolates were screened for the production of the low-calorie sugar mannitol and the biotransformation of Selenium (Se) into its organic forms. Leuconostoc and Fructobacillus strains were capable of producing high quantities of mannitol. In this regard, the fig-origin strain F. tropaeoli CRL 2034 produced 81.9 g/l of mannitol with a yield of 77.5% when applying response surface methodology with central composite design as optimization strategy. Fermentations were carried out at 30 °C and pH 5.0 for 24 h using FYP medium with 165 g/L of total saccharide content and 200 rpm of stirring as optimal culture conditions. In addition, fruit-origin LAB could transform inorganic Se into less toxic and more bioavailable organic forms such as seleno-nanoparticles and seleno-amino acids. Se is an essential micronutrient usually present in the active site of many proteins and its deficiency is associated with oxidative-stress-related diseases. Independently on the microbial species, the majority of the strains could cope with the presence of Se and form nanoparticles (Se0). From the selected strains capable of removing up to 60% of sodium selenite present in the medium, a few could produce selenocysteine in relevant amounts while volatile Se compounds were only produced by the enterococci strains. The formation of organic forms of Se together with mannitol production highlight the potential use of fruit and flower LAB for health-related and industrial applications.