Cutaneous bacteria of the redback salamander prevent morbidity associated with a lethal disease

Abstract

Chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), is an infectious disease that causes population declines of many amphibians. Cutaneous bacteria isolated from redback salamanders, Plethodon cinereus, and mountain yellow-legged frogs, Rana muscosa, inhibit the growth of Bd in vitro. In this study, the bacterial community present on the skin of P. cinereus individuals was investigated to determine if it provides protection to salamanders from the lethal and sub-lethal effects of chytridiomycosis. When the cutaneous bacterial community was reduced prior to Bd exposure, salamanders experienced a significantly greater decrease in body mass, which is a symptom of the disease, when compared to infected individuals with a normal bacterial community. In addition, a greater proportion of infected individuals with a reduced bacterial community experienced limb-lifting, a behavior seen only in infected individuals. Overall, these results demonstrate that the cutaneous bacterial community of P. cinereus provides protection to the salamander from Bd and that alteration of this community can change disease resistance. Therefore, symbiotic microbes associated with this species appear to be an important component of its innate skin defenses.

Figure 1. Proportion of body mass lost over a period of 55 days for treatments Bac−Bd+ (n = 20), Bac+Bd+ (n = 20), and controls (Bac−Bd− and Bac+Bd−, n = 11).

Error bars represent ±1 standard error.

Figure 2. Proportion of individuals in treatments Bac+Bd+ (n = 21), Bac−Bd+ (n = 21), and control (n = 13) that shed skin each week.

Figure 3. Proportion of individuals in treatments Bac+Bd+ (n = 21), Bac−Bd+ (n = 21), and control (n = 13) that lifted their limbs off substrate for at least five minutes each week.