The molecular bases for the symbiosis of the amphibian skin microbiome with its host are poorly understood. Here, we used the odor-producer Pseudomonas sp. MPFS and the treefrog Boana prasina as a model to explore bacterial genome determinants and the resulting mechanisms facilitating symbiosis. Pseudomonas sp. MPFS and its closest relatives, within a new clade of the P. fluoresens Group, have large genomes and were isolated from fishes and plants, suggesting environmental plasticity. We annotated 16 biosynthetic gene clusters from the complete genome sequence of this strain, including those encoding the synthesis of compounds with known antifungal activity and of odorous methoxypyrazines that likely mediate sexual interactions in Boana prasina. Comparative genomics of Pseudomonas also revealed that Pseudomonas sp. MPFS and its closest relatives have acquired specific resistance mechanisms against host antimicrobial peptides (AMPs), specifically two extra copies of a multidrug efflux pump and the same two-component regulatory systems known to trigger adaptive resistance to AMPs in P. aeruginosa. Subsequent molecular modeling indicated that these regulatory systems interact with an AMP identified in Boana prasina through the highly acidic surfaces of the proteins comprising their sensory domains. In agreement with a symbiotic relationship and a highly selective antibacterial function, this AMP did not inhibit the growth of Pseudomonas sp. MPFS but inhibited the growth of another Pseudomonas species and Escherichia coli in laboratory tests. This study provides deeper insights into the molecular interaction of the bacteria-amphibian symbiosis and highlights the role of specific adaptive resistance toward AMPs of the hosts.

两栖动物皮肤微生物组与其宿主共生的分子基础知之甚少。在这里，我们使用了产生气味的假单胞菌。MPFS 和树蛙Boana prasina作为模型来探索细菌基因组决定因素和由此产生的促进共生的机制。假单胞菌_ MPFS 及其近亲，在P. fluoresens 组的一个新进化枝，具有庞大的基因组，并且从鱼类和植物中分离出来，表明环境具有可塑性。我们从该菌株的完整基因组序列中注释了 16 个生物合成基因簇，包括那些编码合成具有已知抗真菌活性的化合物和可能介导性相互作用的有气味甲氧基吡嗪的基因簇Boana prasina的一个新进化枝内。假单胞菌的比较基因组学也揭示了假单胞菌sp。MPFS 及其近亲已经获得了针对宿主抗菌肽 (AMP) 的特异性耐药机制，特别是多药外排泵的两个额外拷贝和已知在铜绿假单胞菌中触发对 AMP 的适应性耐药的相同双组分调节系统。随后的分子模型表明，这些调节系统通过构成其感觉域的蛋白质的强酸性表面与Boana prasina中鉴定的 AMP 相互作用。与共生关系和高度选择性抗菌功能一致，该 AMP 不抑制假单胞菌的生长sp 的生长。MPFS 但抑制另一种假单胞菌和大肠杆菌的生长。这项研究为细菌-两栖动物共生的分子相互作用提供了更深入的见解，并强调了对宿主 AMP 的特异性适应性抗性的作用。