For many flower visitors, pollen is the primary source of non-carbon nutrition, but pollen has physical defenses that make it difficult for consumers to access nutrients. Nectar-dwelling microbes are nearly ubiquitous among flowers and can reach high densities, despite the fact that floral nectar is nitrogen limited, containing only very low concentrations of non-carbon nutrients. Pollen contains trace micronutrients and high protein content but is protected by a recalcitrant outer shell. Here, we report that a common genus of nectar-dwelling bacteria, Acinetobacter, exploits pollen nutrition by inducing pollen germination and bursting. We use time course germination assays to quantify the effect of Acinetobacter species on pollen germination and pollen bursting. Inoculation with Acinetobacter species resulted in increased germination rates within 15 minutes, and bursting by 45 minutes, as compared to uninoculated pollen. The pollen germination and bursting phenotype is density-dependent, with lower concentrations of A. pollinis SCC477 resulting in a longer lag time before the spike in germination, which is then closely followed by a spike in bursting. Lastly, A. pollinis grows to nearly twice the density with germinable pollen vs ungerminable pollen, indicating that their ability to induce and exploit germination plays an important role in rapid growth. To our knowledge, this is the first direct test of non-plant biological induction of pollen germination, as well as the first evidence of induced germination as a method of nutrient procurement, as the microbes appear to hijack the pollens normally tightly controlled germination mechanisms for their benefit. Our results suggest that further study of microbe-pollen interactions may inform many aspects of pollination ecology, including microbial ecology in flowers, the mechanisms of pollinator nutrient acquisition from pollen, and cues of pollen germination for plant reproduction.

中文翻译：

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花蜜细菌刺激花粉萌发和爆发，以增强其适应性

对于许多花卉游客而言，花粉是非碳素营养的主要来源，但花粉具有物理防御作用，使消费者难以获取营养。尽管花蜜是受氮限制的，只含有非常低浓度的非碳营养素，但花蜜中的微生物几乎在花中普遍存在，并且可以达到高密度。花粉含有微量微量营养素和高蛋白含量，但受到顽固的外壳保护。在这里，我们报告说，花蜜居住细菌，不动杆菌属，通过诱导花粉萌发和爆发利用花粉营养。我们使用时程发芽试验来量化不动杆菌属对花粉发芽和花粉爆发的影响。与未接种的花粉相比，接种不动杆菌会导致15分钟内发芽率增加，并破裂45分钟。花粉的发芽和爆发表型是密度依赖性的，较低浓度的A. pollinis SCC477导致发芽高峰之前较长的滞后时间，然后紧接着爆发高峰。最后，在可发芽的花粉与不可发芽的花粉中，花粉曲霉的密度增长到将近两倍，这表明它们诱导和利用发芽的能力在快速生长中起重要作用。据我们所知，这是首次非植物生物诱导花粉萌发的直接测试，也是诱导萌发作为养分获取方法的第一个证据，由于微生物似乎劫持了花粉，因此通常会严格控制其发芽机制以利于它们的生长。我们的结果表明，对微生物-花粉相互作用的进一步研究可能会为授粉生态学的许多方面提供信息，包括花朵中的微生物生态学，从花粉中获取授粉媒介养分的机制以及花粉萌发提示植物繁殖。