AUTHOR=Bell Sara C. , Garland Stephen , Alford Ross A. 

TITLE=Increased Numbers of Culturable Inhibitory Bacterial Taxa May Mitigate the Effects of Batrachochytrium dendrobatidis in Australian Wet Tropics Frogs

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.01604

DOI=10.3389/fmicb.2018.01604

ISSN=1664-302X

ABSTRACT=<p>Symbiotic bacterial communities resident on amphibian skin can benefit their hosts. For example, antibiotic production by community members can control the pathogen <italic>Batrachochytrium dendrobatidis</italic> (<italic>Bd</italic>) and it is possible for these community members to be used as probiotics to reduce infection levels. In the early 1990s, the emergence of <italic>Bd</italic> caused declines and disappearances of frogs in the Australian Wet Tropics; the severity of its effects varied among species and sites. Some species have since recolonized despite enzootic <italic>Bd</italic> within their populations. This variation in history among species and sites provided an opportunity to investigate the role of anti-fungal cutaneous bacteria in protecting frogs against <italic>Bd</italic> infection. We collected cutaneous swab samples from three species of frogs at two upland and two lowland sites in the Wet Tropics, and used <italic>in vitro</italic> challenge assays to identify culturable <italic>Bd</italic>-inhibitory bacterial isolates for further analysis. We sequenced DNA from cultured inhibitory isolates to identify taxa, resulting in the classification of 16 <italic>Bd</italic>-inhibitory OTUs, and determined whether inhibitory taxa were associated with frog species, site, or intensity of infection. We present preliminary results showing that the upper limit of <italic>Bd</italic> infection intensity was negatively correlated with number of inhibitory OTUs present per frog indicating that increased numbers of <italic>Bd</italic>-inhibiting taxa may play a role in reducing the intensity of <italic>Bd</italic> infections, facilitating frog coexistence with enzootic <italic>Bd</italic>. One upland site had a significantly lower prevalence of <italic>Bd</italic> infection, a significantly higher proportion of frogs with one or more culturable <italic>Bd</italic>-inhibitory OTUs, a greater number of inhibitory bacterial genera present per frog, and statistically significant clustering of individual frogs with similar <italic>Bd</italic>-inhibitory signatures when compared to all other sites. This suggests that <italic>Bd</italic>-inhibitory taxa are likely to be particularly important to frogs at this site and may have played a role in their ability to recolonize following population declines. Our findings suggest that the use of multi-taxon <italic>Bd</italic>-inhibitory probiotics to support at-risk amphibian populations may be more effective than single-taxon alternatives.</p>