Effects of glyphosate herbicide on the gastrointestinal microflora of Hawaiian green turtles (Chelonia mydas) Linnaeus

Abstract

In Hawaii, glyphosate-based herbicides frequently sprayed near shorelines may be affecting non-target marine species. Glyphosate inhibits aromatic amino acid biosynthesis (shikimate pathway), and is toxic to beneficial gut bacteria in cattle and chickens. Effects of glyphosate on gut bacteria in marine herbivorous turtles were assessed in vitro. When cultures of mixed bacterial communities from gastrointestinal tracts of freshly euthanized green turtles (Chelonia mydas), were exposed for 24h to six glyphosate concentrations (plus deionized water control), bacterial density was significantly lower at glyphosate concentrations≥2.2×10^-4gL^-1 (absorbance measured at 600nm wavelength). Using a modified Kirby-Bauer disk diffusion assay, the growth of four bacterial isolates (Pantoea, Proteus, Shigella, and Staphylococcus) was significantly inhibited by glyphosate concentrations≥1.76×10^-3gL^-1. Reduced growth or lower survival of gut bacteria in green turtles exposed to glyphosate could have adverse effects on turtle digestion and overall health.

Keywords: Bacteria; Digestion; Glyphosate toxicity; Green turtle; Hawaii; Microbial communities.