Hovey Kyle J, Seiter Emily M, Johnson Erin E, Saporito Ralph A
Department of Biology, John Carroll University, University Heights, OH, 44118, USA.
J Chem Ecol. 2018 Mar;44(3):312-325. doi: 10.1007/s10886-018-0930-8. Epub 2018 Feb 10.
Most amphibians produce their own defensive chemicals; however, poison frogs sequester their alkaloid-based defenses from dietary arthropods. Alkaloids function as a defense against predators, and certain types appear to inhibit microbial growth. Alkaloid defenses vary considerably among populations of poison frogs, reflecting geographic differences in availability of dietary arthropods. Consequently, environmentally driven differences in frog defenses may have significant implications regarding their protection against pathogens. While natural alkaloid mixtures in dendrobatid poison frogs have recently been shown to inhibit growth of non-pathogenic microbes, no studies have examined the effectiveness of alkaloids against microbes that infect these frogs. Herein, we examined how alkaloid defenses in the dendrobatid poison frog, Oophaga pumilio, affect growth of the known anuran pathogens Aeromonas hydrophila and Klebsiella pneumoniae. Frogs were collected from five locations throughout Costa Rica that are known to vary in their alkaloid profiles. Alkaloids were isolated from individual skins, and extracts were assayed against both pathogens. Microbe subcultures were inoculated with extracted alkaloids to create dose-response curves. Subsequent spectrophotometry and cell counting assays were used to assess growth inhibition. GC-MS was used to characterize and quantify alkaloids in frog extracts, and our results suggest that variation in alkaloid defenses lead to differences in inhibition of these pathogens. The present study provides the first evidence that alkaloid variation in a dendrobatid poison frog is associated with differences in inhibition of anuran pathogens, and offers further support that alkaloid defenses in poison frogs confer protection against both pathogens and predators.
大多数两栖动物会自行产生防御性化学物质；然而，箭毒蛙则从其摄食的节肢动物中获取基于生物碱的防御物质。生物碱起到抵御捕食者的作用，某些类型的生物碱似乎还能抑制微生物生长。箭毒蛙种群之间的生物碱防御差异很大，这反映出其摄食的节肢动物在地理分布上的差异。因此，环境驱动的青蛙防御差异可能对其抵御病原体具有重要意义。虽然最近已证明树棘蛙科箭毒蛙体内的天然生物碱混合物可抑制非致病性微生物的生长，但尚无研究考察生物碱对感染这些青蛙的微生物的有效性。在此，我们研究了树棘蛙科箭毒蛙——草莓箭毒蛙的生物碱防御如何影响已知的蛙类病原体嗜水气单胞菌和肺炎克雷伯菌的生长。从哥斯达黎加的五个地点采集了青蛙，这些地点的生物碱谱已知存在差异。从个体蛙的皮肤中分离出生物碱，并对提取物针对两种病原体进行检测。将微生物传代培养物接种提取的生物碱以绘制剂量反应曲线。随后使用分光光度法和细胞计数测定法评估生长抑制情况。利用气相色谱 - 质谱联用技术对青蛙提取物中的生物碱进行表征和定量，我们的结果表明生物碱防御的差异导致对这些病原体抑制作用的不同。本研究首次证明树棘蛙科箭毒蛙的生物碱差异与对蛙类病原体抑制作用的差异相关，并进一步支持了箭毒蛙的生物碱防御能同时抵御病原体和捕食者的观点。
