IDENTIFICATION OF ANTIMICROBIAL Peptides in CLOACAL FLUID FROM LOGGERHEAD TURTLES (CARETTA CARETTA)

Microbial pathogens are a significant threat to sea turtle reproductive success, often reducing hatchling production and increasing embryo mortality. Sea turtles rely on innate immune defenses, also known as antimicrobial peptides (AMPs), to combat these pathogens. While AMPs are widespread across a variety of organisms, including vertebrates and invertebrates, reptile-derived AMPs remain understudied. This study aimed to isolate and characterize antimicrobial peptides and other agents from the cloacal fluid of loggerhead sea turtles (Caretta caretta). Cloacal fluid samples were collected during the 2024 nesting season at Wassaw National Wildlife Refuge, Georgia. Samples were concentrated using ultracentrifugal filtration (3K molecular weight cut-off) and fractionated through size-exclusion chromatography (SEC) into 65 fractions. Antimicrobial activity of both crude extracts and peptide fractions was evaluated using antimicrobial plate assays, with select fractions subjected to mass spectrometry. Results demonstrated that loggerhead cloacal fluid possesses antimicrobial activity against Escherichia coli. Mass spectrometry was used to identify proteins with molecular weights ranging from approximately 5 to 250 kDa, some of which carry known antimicrobial activity. These findings highlight the potential of loggerhead cloacal fluid as a source of novel antimicrobial agents. Future research should explore recombinant production of key proteins and other agents identified, optimize peptide identification methods, and assess antimicrobial activity against more bacterial pathogens, particularly those affecting the sea turtle nests.