Environ Exp Biol (2025) 23: 89–94

Isolation and characterization of novel bacteria Macrococcus canis from the gut of the freshwater fish Macrognathus spp.

Abstract

Macrococcus canis was isolated from the gut of the omnivorous freshwater fish Macrognathus spp. In the 16S rRNA gene sequence, the bacterial isolate M2 showed a 99.43% similarity with Macrococcus canis (accession NR_156154.1). M. canis was found to be morphologically a Gram-positive and non-motile cocci-shaped bacterium that formed smooth, yellowish-orange, convex colonies approximately 2 mm in diameter. According to biochemical characterization, M. canis had positive reactions for Voges-Proskauer, oxidase, catalase, and nitrate reduction and negative reactions for urease, indole, citrate, methyl red, and urease. Furthermore, the isolate M. canis had positive lipase and protease activity, suggesting that it may play a role in lipid and protein metabolism within the fish gut microbiota. The results provide evidence that M. canis colonizes a new habitat – the aquatic environment, as previous studies already pointed to the existence of Macrococcus species within the fish gut microbiota. Additional studies, such as whole gene sequence and functional tests, would be required to understand the ecological and physiological roles of M. canis in water-living organisms.