Data_Sheet_1_Direct Evidence That Sunbirds’ Gut Microbiota Degrades Floral Nectar’s Toxic Alkaloids.pdf

Orange-tufted sunbirds (Cinnyris osea) feed on the nectar of the tobacco tree (Nicotiana glauca) which contains toxic pyridine alkaloids characterized by high concentrations of anabasine and much lower concentrations of nicotine. We aimed at determining whether the gut microbiota of sunbirds harbors bacterial species that enable the birds to cope with these toxic alkaloids. An in vivo experiment that included 12 birds showed that inducing dysbiosis in sunbirds’ guts by the addition of sulfamethoxazole and trimethoprim, significantly reduced the birds’ ability to degrade anabasine (n = 3) compared to control birds (n = 3) with undisturbed microbiota. Sunbirds whose gut bacterial communities were altered by the antibacterial agents and who were fed with added nicotine, also showed a lower percentage of nicotine degradation (n = 3) in their excreta compared to the sunbirds with undisturbed microbiota (n = 3), though this difference was not significant. In an in vitro experiment, we studied the ability of Lactococcus lactis, Enterobacter hormaechei, Chryseobacterium gleum, Kocuria palustris, and Methylorubrum populi that were isolated from sunbirds’ excreta, to degrade anabasine and nicotine. By using gas chromatography-mass spectrometry (GC-MS) analysis, we successfully demonstrated, for the first time, the ability of these species to degrade the focal secondary metabolites. Our findings demonstrate the role of gut bacteria in detoxifying toxic secondary metabolites found in the N. glauca nectar. The degradation products may supply the birds with nitrogen which is scarce in nectar-rich diets. These findings support another role of bacteria in mediating the interactions between plants and their pollinators.

橙簇花蜜鸟（Cinnyris osea）取食光烟草（Nicotiana glauca）的花蜜，该花蜜含有以高浓度假木贼碱（anabasine）和低浓度尼古丁（nicotine）为特征的有毒吡啶生物碱（pyridine alkaloids）。本研究旨在明确花蜜鸟的肠道菌群是否携带可帮助鸟类耐受这些有毒生物碱的细菌物种。一项包含12只受试鸟的体内实验（in vivo experiment）显示：通过添加磺胺甲恶唑（sulfamethoxazole）与甲氧苄啶（trimethoprim）诱导花蜜鸟肠道菌群失调后，与菌群未受干扰的对照组（n=3）相比，处理组（n=3）鸟类降解假木贼碱的能力显著下降。对于肠道菌群被抗菌剂改变且喂食了添加型尼古丁的花蜜鸟，其排泄物中的尼古丁降解率同样低于菌群未受干扰的对照组（n=3），尽管该差异未达到统计学显著性水平。在体外实验（in vitro experiment）中，我们研究了从花蜜鸟排泄物中分离得到的乳酸乳球菌（Lactococcus lactis）、霍氏肠杆菌（Enterobacter hormaechei）、格氏金黄杆菌（Chryseobacterium gleum）、沼泽库特菌（Kocuria palustris）以及杨树甲基杆菌（Methylorubrum populi）降解假木贼碱与尼古丁的能力。借助气相色谱-质谱联用（GC-MS）分析，我们首次成功证实了上述菌株可降解目标次生代谢物。本研究结果证实了肠道细菌在解毒光烟草花蜜中有毒次生代谢物方面的作用，其降解产物可为鸟类补充花蜜饮食中稀缺的氮源。上述发现进一步支持了细菌在介导植物与其传粉者间相互作用中的另一重要功能。