Department of Biology, San Diego State University, San Diego, CA 92182, USA.
Department of Entomology and Nematology, University of California, Davis, Davis, CA 95616, USA.
FEMS Microbiol Ecol. 2020 Mar 1;96(3). doi: 10.1093/femsec/fiaa003.
Microbial dispersal is essential for establishment in new habitats, but the role of vector identity is poorly understood in community assembly and function. Here, we compared microbial assembly and function in floral nectar visited by legitimate pollinators (hummingbirds) and nectar robbers (carpenter bees). We assessed effects of visitation on the abundance and composition of culturable bacteria and fungi and their taxonomy and function using shotgun metagenomics and nectar chemistry. We also compared metagenome-assembled genomes (MAGs) of Acinetobacter, a common and highly abundant nectar bacterium, among visitor treatments. Visitation increased microbial abundance, but robbing resulted in 10× higher microbial abundance than pollination. Microbial communities differed among visitor treatments: robbed flowers were characterized by predominant nectar specialists within Acetobacteraceae and Metschnikowiaceae, with a concurrent loss of rare taxa, and these resulting communities harbored genes relating to osmotic stress, saccharide metabolism and specialized transporters. Gene differences were mirrored in function: robbed nectar contained a higher percentage of monosaccharides. Draft genomes of Acinetobacter revealed distinct amino acid and saccharide utilization pathways in strains isolated from robbed versus pollinated flowers. Our results suggest an unrecognized cost of nectar robbing for pollination and distinct effects of visitor type on interactions between plants and pollinators. Overall, these results suggest vector identity is an underappreciated factor structuring microbial community assembly and function.
微生物的扩散对于在新栖息地的建立至关重要，但在群落组装和功能方面，载体身份的作用还了解甚少。在这里，我们比较了由合法传粉者（蜂鸟）和花蜜掠夺者（木匠蜂）访问的花卉花蜜中的微生物组装和功能。我们使用鸟枪法宏基因组学和花蜜化学方法评估了访问对可培养细菌和真菌的丰度和组成及其分类和功能的影响。我们还比较了在访客处理中常见且高度丰富的花蜜细菌不动杆菌的宏基因组组装基因组（MAG）。访问增加了微生物的丰度，但掠夺导致的微生物丰度比授粉高 10 倍。微生物群落因访客处理而异：掠夺花朵的特征是在醋酸杆菌科和 Metschnikowiaceae 内占主导地位的花蜜专性细菌，同时稀有分类群的丧失，这些群落中存在与渗透胁迫、糖代谢和专门转运体相关的基因。功能上也存在差异：掠夺的花蜜中含有更高比例的单糖。从掠夺和授粉花朵中分离出的不动杆菌的草图基因组揭示了不同的氨基酸和糖利用途径。我们的研究结果表明，花蜜掠夺对授粉是一种未被认识到的代价，并且访客类型对植物和传粉者之间的相互作用有明显的影响。总的来说，这些结果表明，载体身份是一个被低估的因素，它影响着微生物群落组装和功能。
