Table_2_Tropical Palm Endophytes Exhibit Low Competitive Structuring When Assessed Using Co-occurrence and Antipathogen Activity Analysis.xlsx

Leaf-inhabiting fungal and bacterial endophytes are at their most diverse in tropical rainforest plant hosts, with some influencing host plant fitness as either symbionts or pathogens. Endophyte activity and community composition is thought to depend on competition amongst co-occurring species for resources. Here, we reveal the strength of competitive interactions between endophytes by combining e-DNA metabarcoding to characterize the community with culturing assays to ascertain their potential activity. The endophyte community associated with the understory palm Astrocaryum sciophilum was determined by extracting eDNA from 120 leaflets of eight plants located in a lowland rainforest in French Guiana. This revealed 516 fungal and 606 bacterial Operational Taxonomic Units (OTUs). Co-occurrence analysis of the most abundant OTUs revealed that direct fungal-fungal interactions were overall more negative than bacterial-bacterial interactions. This was confirmed by C-score calculations for the whole endophyte community, revealing significantly greater levels of species segregation for fungi but not bacteria when compared with simulated random communities. Following the culturing of 131 fungal, and 66 bacterial Astrocaryum endophytes collected from the same leaves, Minimal Inhibitory Concentrations of ethyl acetate culture extracts were evaluated against the fungus Trichophyton rubrum and the bacterium Staphylococcus aureus. Overall, a minority of extracts demonstrated antipathogen activity, with greater antifungal activity expression for both fungi and bacteria when compared with antibacterial activity. In order to explore whether this activity translated into competitive structuring of the community, a BLAST was conducted to match metabarcoding sequences with Sanger derived culture sequences. This demonstrated that cultures displaying antipathogen activity were significantly more likely to co-occur with fungi if they were bacteria, and bacteria if they were fungi. Nevertheless, overall correlation values averaged around zero. These results indicate that for Astrocaryum palms, fungal endophytes are likely to play a greater role in determining colonization success of subsequent endophytes whether these be fungal or bacterial, but that overall endophyte communities do not display strong patterns of community structuring through competition. Endophyte communities are thus likely to reach relative stasis in mature leaves, where the diverse community of fungi and bacteria amongst other factors prevent the subsequent establishment of pathogens.

栖息于叶片的真菌与细菌内生菌（endophytes）在热带雨林宿主植物中多样性最高，其中部分类群作为共生体或病原菌影响宿主植物的适合度。学界认为，内生菌的活性与群落组成取决于共存物种间对资源的竞争作用。本研究通过结合环境DNA条形码测序（e-DNA metabarcoding）表征群落结构与培养实验以明确其潜在活性，揭示了内生菌间竞争互作的强度。本研究从法属圭亚那一处低地雨林的8株宿主植物的120片小叶中提取环境DNA，明确了林下棕榈Astrocaryum sciophilum的关联内生菌群落。此次分析共鉴定出516个真菌与606个细菌操作分类单元（Operational Taxonomic Units，OTUs）。对丰度最高的OTUs进行共现分析后发现，真菌间的直接相互作用整体上较细菌间的相互作用具有更强的负向效应。通过对整个内生菌群落进行C得分计算，验证了这一结论：与模拟随机群落相比，真菌类群的物种分隔程度显著更高，而细菌类群则无此现象。在从相同叶片中分离培养得到131株真菌与66株细菌Astrocaryum内生菌后，本研究评估了乙酸乙酯培养提取物的最低抑菌浓度（Minimal Inhibitory Concentrations，MIC），以测试其对红色毛癣菌（Trichophyton rubrum）与金黄色葡萄球菌（Staphylococcus aureus）的抑制活性。整体而言，仅有少数提取物表现出抗病原菌活性；相较于抗菌活性，真菌与细菌来源的提取物均展现出更强的抗真菌活性。为探究此类活性是否会推动群落形成竞争性结构，本研究开展了BLAST（Basic Local Alignment Search Tool）比对，将条形码测序得到的序列与桑格测序获得的培养序列进行匹配。结果显示，具有抗病原菌活性的培养物：若为细菌，则更易与真菌类群共现；若为真菌，则更易与细菌类群共现。尽管如此，整体的相关性均值趋近于零。上述结果表明，对于Astrocaryum属棕榈而言，真菌内生菌在决定后续内生菌（无论为真菌还是细菌）的定殖成功率方面可能发挥着更重要的作用；但整体而言，内生菌群落并未通过竞争形成显著的群落结构模式。因此，成熟叶片中的内生菌群落可能会达到相对稳定的状态：其中多样的真菌与细菌群落等多种因素，可阻止后续病原菌的定殖。