Exploring Autochthonous Probiotics From Hybrid Catfish (Ictalurus punctatus × I. furcatus)

1,2Jing Huang, 3Heather Jordan, 4Caitlin E. Older, 1,5Matt J. Griffin, 2Peter J. Allen, 1,2David J. Wise, 1Penelope M. Goodman, 1J. Grant Reifers, and 1,2Fernando Y. Yamamoto

1Thad Cochran National Warmwater Aquaculture Center, Mississippi Agriculture and Forestry; Experiment Station, Mississippi State University, Stoneville, MS 38776; 2Department of Wildlife, Fisheries, and Aquaculture, College of Forest Resources, Mississippi State University, Starkville, MS 39762; 3Department of Biology, Mississippi State University, Starkville, MS 39762; 4Warmwater Aquaculture Research Unit, Agriculture Research Service, Department of Agriculture, Stoneville, MS, 39762; 5Department of Pathobiology and Population Medicine, College of Veterinary Medicine, Mississippi State University, Stoneville, MS, 38776

ABSTRACT

Autochthonous probiotics have shown better colonization and adaption to the host’s intestine compared to heterogeneous strains. The identification of an efficient autochthonous probiotic may improve hybrid catfish (Ictalurus punctatus × I. furcatus) production performance and disease resistance. In this study, the intestinal microbiota structure of overperforming and underperforming hybrid catfish reared in experimental earthen ponds was compared using next-generation sequencing of the 16S rRNA gene (V4 region). The relative abundance of Cetobacterium spp. was found significantly higher in underperforming fish, while Lactococcus spp. and Turicibacter spp. had higher relative abundances in overperforming fish.  A total of 42 lactic acid bacteria were isolated from overperforming fish and evaluated as potential probiotics. Among those, Lactococcus lactis isolate MA5 stood out from other candidates, revealing robust proteolytic and lipolytic activity, and demonstrated antagonistic inhibition of the gram-negative catfish pathogens Aeromonas hydrophila, Edwardsiella ictaluri, and E. piscicida. A biosafety assessment was conducted to ensure the isolated candidates were safe and did not demonstrate antibiotic resistance. To further understand the potential of this isolate, in silica whole genome sequencing (WGS) was performed and analyzed for putative probiotic traits. L. lactis isolate MA5 contains genes for synthesis of the vitamins B1, B2, B6, B7, B9 and as well as genes putatively associated with temperature, acid, bile salt, and osmotic stress tolerance. Moreover, three discrete bacteriocins, as well as lactic acid producing genes were identified, providing some evidentiary support for the observed antagonism of L. lactis isolate MA5 against target pathogens. Overall, the demonstrated phenotype indicates L. lactis isolate MA5 bacteria has potential to be an effective probiotic to enhance health and productivity in hybrid catfish.