University of Nairobi, Department of Biochemistry, 00200-30197, Nairobi, Kenya.
Helmholtz Centre for Environmental Research UFZ, Department of Environmental Microbiology, 04318, Leipzig, Germany.
ISME J. 2023 Apr;17(4):570-578. doi: 10.1038/s41396-023-01371-7. Epub 2023 Jan 27.
Biotransformation of soil organochlorine pesticides (OCP) is often impeded by a lack of nutrients relevant for bacterial growth and/or co-metabolic OCP biotransformation. By providing space-filling mycelia, fungi promote contaminant biodegradation by facilitating bacterial dispersal and the mobilization and release of nutrients in the mycosphere. We here tested whether mycelial nutrient transfer from nutrient-rich to nutrient-deprived areas facilitates bacterial OCP degradation in a nutrient-deficient habitat. The legacy pesticide hexachlorocyclohexane (HCH), a non-HCH-degrading fungus (Fusarium equiseti K3), and a co-metabolically HCH-degrading bacterium (Sphingobium sp. S8) isolated from the same HCH-contaminated soil were used in spatially structured model ecosystems. Using C-labeled fungal biomass and protein-based stable isotope probing (protein-SIP), we traced the incorporation of C fungal metabolites into bacterial proteins while simultaneously determining the biotransformation of the HCH isomers. The relative isotope abundance (RIA, 7.1-14.2%), labeling ratio (LR, 0.13-0.35), and the shape of isotopic mass distribution profiles of bacterial peptides indicated the transfer of C-labeled fungal metabolites into bacterial proteins. Distinct C incorporation into the haloalkane dehalogenase (linB) and 2,5-dichloro-2,5-cyclohexadiene-1,4-diol dehydrogenase (LinC), as key enzymes in metabolic HCH degradation, underpin the role of mycelial nutrient transport and fungal-bacterial interactions for co-metabolic bacterial HCH degradation in heterogeneous habitats. Nutrient uptake from mycelia increased HCH removal by twofold as compared to bacterial monocultures. Fungal-bacterial interactions hence may play an important role in the co-metabolic biotransformation of OCP or recalcitrant micropollutants (MPs).
土壤有机氯农药（OCP）的生物转化常常受到与细菌生长和/或共代谢 OCP 生物转化相关的营养物质缺乏的阻碍。真菌通过提供空间填充的菌丝体，促进了污染物的生物降解，使细菌得以扩散，并在菌根圈内使营养物质得以移动和释放。在这里，我们测试了菌丝体从营养丰富的区域向营养匮乏的区域转移营养物质是否有助于在营养匮乏的生境中促进细菌对 OCP 的降解。使用来自同一 HCH 污染土壤的非六氯环己烷（HCH）降解真菌（镰刀菌 equiseti K3）和共代谢 HCH 降解细菌（鞘氨醇单胞菌 S8），以及 legacy 农药六氯环己烷（HCH），在空间结构模型生态系统中进行了测试。利用 C 标记的真菌生物量和基于蛋白质的稳定同位素探测（protein-SIP），我们追踪了 C 真菌代谢物掺入细菌蛋白质的情况，同时还测定了 HCH 异构体的生物转化情况。细菌肽的相对同位素丰度（RIA，7.1-14.2%）、标记比（LR，0.13-0.35）和同位素质量分布曲线的形状表明了 C 标记的真菌代谢物向细菌蛋白质的转移。卤代烷脱卤酶（linB）和 2,5-二氯-2,5-环己二烯-1,4-二醇脱氢酶（LinC）的独特 C 掺入，这两种酶是代谢 HCH 降解的关键酶，这为菌丝体营养物质运输和真菌-细菌相互作用在异质生境中对共代谢细菌 HCH 降解的作用提供了依据。与细菌单培养相比，从菌丝体中吸收营养物质使 HCH 的去除量增加了一倍。因此，真菌-细菌相互作用可能在 OCP 或难降解微量污染物（MPs）的共代谢生物转化中发挥重要作用。
