Identification of new yeast strains, Candida zeylanoides Y12-3 and Hyphopichia pseudoburtonii Y12-1, from the intestinal tract of rainbow trout, Oncorhynchus mykiss, with potential probiotic characteristics

In this study, 2 yeasts, Candida zeylanoides isolate Y12-3 (MN073455.1) and Hyphopichia pseudoburtonii isolate Y12-1 (MN073489.1), were isolated from rainbow trout hindguts. Their identity was confirmed by amplification of internal transcribed spacer (ITS) gene regions. Their in vitro probiotic properties showed that they were hydrophobic and did not inhibit bacterial growth. However, they displayed positive co-aggregation with several bacterial pathogens. It was interesting that Y12-1 and Y12-3 isolates survived and grew well in bile salt concentrations ranging from 0.6% to 1.5% and at low pH conditions. After a 35-day feeding trial, the results of dietary incorporation of the yeast isolates showed that serum myeloperoxidase activity was unchanged in the treated and control groups. Meanwhile, serum lysozyme activity in yeast groups was decreased significantly compared to the control. However, fish fed with Y12-1 had higher total protein, albumin, and globulin than other groups. Total cholesterol levels were decreased significantly in yeast groups compared to the control. Interestingly, the Y12-1 and Y12-3 groups showed higher survival (69.05% and 80.95%) after the challenge with Lactococcus garvieae compared to the control (45.24%). In brief, the aforementioned findings showed that Y12-1 and Y12-3 strains could be potential probiotic candidates for use in rainbow trout farming.