# Influence of Naturally Occurring Bacteria on Embryonic and Larval Development of Common Toad Tadpoles

## TL;DR

This study shows that naturally occurring bacteria can affect the development of common toad tadpoles by altering their physiology and energy levels.

## Contribution

The study demonstrates that specific bacteria influence amphibian development through physiological changes.

## Key findings

- Sterilized habitat water supported the highest development of toad eggs and tadpoles.
- Bacterial exposure decreased acetylcholinesterase activity but increased tadpole size and energy budget.
- Native microbial communities had a negative effect on tadpole development.

## Abstract

To investigate the impact of bacteria on the embryonic and larval development of the common toad (Bufo bufo), eggs and tadpoles were exposed under laboratory conditions to bacteria (Bacillus sp., Mesobacillus sp.) isolated from the habitat water. Pure bacterial cultures and their combinations decreased acetylcholinesterase activity but had positive effects on tadpole size and energy budget. These findings suggest that bacteria can influence the larval development of common toads by modifying physiological traits. Future research should elucidate which microbes have beneficial or detrimental effects on amphibian development.

Amphibians, as the most threatened group of vertebrates, are the focus of investigation of various agents that could affect their fitness and survival. In this context, we examined the effects of naturally occurring bacteria and their combinations on the embryonic and larval development of common toad tadpoles (Bufo bufo). One egg string that was collected from the wild was disinfected in the lab and divided into short strings, each containing 20 eggs. These strings were exposed to three different control treatments, i.e., a sterile FETAX solution, water collected from the tadpoles’ native habitat, and sterilized habitat water, as well as to three different bacterial cultures isolated from habitat water (Bacillus sp., Mesobacillus sp.). We analyzed several morphometric variables (snout–vent length, total length, and weight), the energy budget by measuring body composition (proteins, carbohydrates, and lipids), and biomarker activity (acetylcholinesterase and lactate dehydrogenase). Our results indicate that the native microbial community had a negative effect on egg and tadpole development, as sterilized habitat water supported their highest development. Additionally, when grown in FETAX, pure bacterial cultures and their combinations decreased acetylcholinesterase activity but positively affected both tadpole size and energy budget. These findings suggest that bacteria can influence the larval development of common toads by modifying physiological traits. Future research should identify which microbes have beneficial or detrimental effects on amphibian development.