Recent molecular surveys revealed an unexpected diversity of mycoplankton in lakes and oceans. The early diverging fungal lineages are known to be prominent parasites of phytoplankton. However, due to missing fungal reference data, their identity and ecology remain mostly unknown. To overcome this problem, we combined single‐spore‐based DNA barcoding during one sampling season of the eutrophic Lake Inba (Japan), which is dominated by two diatoms. By linking microscopically picked single fungal spore on two diatoms to subsequent DNA barcoding of ribosomal maker genes, we identified 12 distinct lineages, affiliated not only to the known parasitic phylum Chytridiomycota (chytrids), but also to the enigmatic phyla Rozellomycota and Aphelidiomycota. The detected Rozellomycota could be a hyperparasite of parasitic chytrid infecting diatoms. Host specificity appeared to be different among clades. However, the barcoding of single‐spore DNA could not clearly prove host specificity due to the limited number of samples and resolution in the targeted gene regions. The degree of host specificity was thus confirmed by the cross‐infection experiments. Five chytrid strains were generalists infecting all four diatoms strains, while the remaining three strains of chytrids were specialists exhibiting host preferences. Additional growth experiments indicated a trade‐off between host specificity and growth rate, so that generalists with more possible hosts grew slower than specialists with one host. Our results suggest that the combination of microscopy with single‐spore‐based barcoding is a promising approach to evaluate the complex host‐parasite interactions, while infection experiments can verify the interactions and shed light on the underlying ecological principles.

中文翻译：

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单个优势硅藻可以寄主不同程度的寄主特异性的多种寄生真菌

最近的分子调查显示，湖泊和海洋中浮游生物的出乎意料的多样性。早期发散的真菌谱系是浮游植物的主要寄生虫。然而，由于缺少真菌参考数据，它们的身份和生态学仍然鲜为人知。为了克服这个问题，我们在富营养化的印巴湖（日本）的一个采样季节中结合了基于单孢子的DNA条形码，该湖由两个硅藻主导。通过将两个硅藻上的显微采摘的单个真菌孢子与核糖体制造者基因的后续DNA条形码连接，我们鉴定了12个不同的谱系，不仅与已知的寄生门菌Chytridiomycota（chytrids）有关，而且还与神秘的Rozellomycota和Aphelidiomycota属有关。所检测到的Rozellomycota可能是感染了硅藻的寄生性chytrid的超寄生虫。进化枝之间的宿主特异性似乎不同。但是，由于样品数量有限和目标基因区域的分辨率，单孢子DNA的条形码无法清楚地证明宿主特异性。因此，通过交叉感染实验确认了宿主特异性的程度。五种糜蛋白酶菌株是通感染所有四个硅藻菌株的通才，而其余三株糜蛋白酶菌株则是表现出宿主偏好的专家。额外的增长实验表明，宿主特异性和增长率之间需要权衡，因此拥有更多可能宿主的通才比拥有一个宿主的专家增长慢。我们的结果表明，将显微镜与基于单孢子的条形码结合起来是一种评估复杂的宿主-寄生虫相互作用的有前途的方法，