Study of the biodiversity of technologically interesting yeast flora isolated from raw camel milk

Résumé

The purpose of this thesis was to isolate yeasts from Algerian biotopes and characterize strains that have interesting technological properties. For this, the biotope we chose for this study was raw camel milk, this choice was based on the peculiarity of this ecosystem as well as the lack of data on the diversity of yeasts in raw camel milk. This study focused on the characterization of the biodiversity of the yeast microflora hosted in raw camel milk collected in Algeria in the wilayas of Ghardaia, Bechar, El Bayadh, Djelfa et Biskra. The results of this study revealed that the number of yeasts was estimated at 3.55 × 102 CFU mL-1, with a maximum of 6.3 × 102 CFU mL-1. The yeasts were classified phenotypically by API 20C AUX, then genetically identified by sequencing the 26S rDNA and ITS1-5.8S-ITS2. These identifications led to the creation of a contingent of 12 species, including, Trichosporon asahii, Rhodotorula mucilaginosa, Pichia fermentans, Millerozyma farinosa, Pichia galeiformis, Candida tartarivorans, Pichia manshurica, Clavispora lusitaniae, Candida zeylanoides, Candida parapsilosis, Klyuveromyces marxianus et Candida maris. In addition, the impact of seasonality and environmental conditions on this diversity was assessed, for which we found a significant difference between autumn and spring. Raw camel milk is more colonized by yeasts during the autumn season in the semi-arid climate region than during the spring season. In addition, in terms of diversity, the vast majority of species, 11 species, were identified during the autumn season. Conversly to the spring season when only 6 species were encountered. However, T. asahii, R. mucilaginosa, P. fermentans, C. parapsilosis and C. zeylanoides were found in both seasons. It should be noted that, according to the bibliographic data, no previous studies on the diversity of yeasts in raw camel milk have been able to identify the following species: Trichosporon asahii, Millerozyma farinosa, Pichia galeiformis, Candida tartarivorans, Pichia manshurica and Pichia fermentans. This study also focused on the technological properties of yeasts, particularly the antagonism of yeasts towards a broad spectrum of microorganisms including fungi, Gram- positive and Gram-negative bacteria. This has led us to characterize this capacity only in the Trichosporon asahii ICVY021 strain, against only one target bacteria Kocuria rhizophila CIP 53.45, due to the production of an antibacterial peptide, which has been called P16 / Oranicine. This peptide was studied using the LC-MS / MS technique, and its partial amino acid sequence was PPFPK and CTHV (L / I) (K / Q) or TCHV (L / I) (K / Q). furthermore, this peptide is believed to interfer with the cell division mechanism. It is interesting to note the safety of T. asahii, as it did not show any hemolytic activity or any cytotoxicity effect against eukaryotic Caco-2 cells. Finally, T. asahii ICVY021 was sensitive to azole antifungal compounds, but not to 5-fluorocytosine and anidulafungin. To our knowledge, our study is the only one which has demonstrated that food-borne T. asahii could secrete an antibacterial peptide with a very narrow spectrum.

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