Impact of Phanerochaete chrysosporium on the Functional Diversity of Bacterial Communities Associated with Decaying Wood

Bacteria and fungi naturally coexist in various environments including forest ecosystems. While the role of saprotrophic basidiomycetes in wood decomposition is well established, the influence of these fungi on the functional diversity of the wood-associated bacterial communities has received much less attention. Based on a microcosm experiment, we tested the hypothesis that both the presence of the white-rot fungus Phanerochaete chrysosporium and the wood, as a growth substrate, impacted the functional diversity of these bacterial communities. Microcosms containing sterile sawdust were inoculated with a microbial inoculum extracted from a forest soil, in presence or in absence of P. chrysosporium and subsequently, three enrichment steps were performed. First, bacterial strains were isolated from different microcosms previously analyzed by 16S rRNA gene-based pyrosequencing. Strains isolated from P. chrysosporium mycosphere showed less antagonism against this fungus compared to the strains isolated from the initial forest soil inoculum, suggesting a selection by the fungus of less inhibitory bacterial communities. Moreover, the presence of the fungus in wood resulted in a selection of cellulolytic and xylanolytic bacterial strains, highlighting the role of mycospheric bacteria in wood decomposition. Additionally, the proportion of siderophore-producing bacteria increased along the enrichment steps, suggesting an important role of bacteria in iron mobilization in decaying-wood. Finally, taxonomic identification of 311 bacterial isolates revealed, at the family level, strong similarities with the high-throughput sequencing data as well as with other studies in terms of taxonomic composition of the wood-associated bacterial community, highlighting that the isolated strains are representative of the wood-associated bacterial communities.

细菌与真菌可在包括森林生态系统在内的各类自然环境中共存。尽管腐生担子菌（saprotrophic basidiomycetes）在木材分解中的作用已得到广泛证实，但这类真菌对木材相关细菌群落（wood-associated bacterial communities）功能多样性的影响却鲜有研究关注。本研究基于微宇宙实验（microcosm experiment），验证了“白腐真菌（white-rot fungus）黄孢原毛平革菌（Phanerochaete chrysosporium）的存在与作为生长底物的木材，均会影响这类细菌群落的功能多样性”这一假说。本研究将搭载无菌锯屑的微宇宙接种从森林土壤提取的微生物接种物，设置有、无黄孢原毛平革菌两个实验组别，随后完成三轮富集培养流程。首先，从此前经基于16S rRNA基因的焦磷酸测序分析的不同微宇宙样本中分离细菌菌株。相较于从初始森林土壤接种物分离得到的菌株，从黄孢原毛平革菌菌际（mycosphere）分离的菌株对该真菌的拮抗活性更弱，提示该真菌筛选出了拮抗能力较弱的细菌群落。此外，木材中真菌的存在筛选出了纤维素分解与木聚糖分解细菌菌株，凸显了菌际细菌在木材分解过程中的作用。同时，产铁载体（siderophore-producing）细菌的占比随富集步骤推进逐渐升高，表明细菌在腐朽木材的铁动员过程中发挥关键作用。最后，对311株细菌分离物的分类学鉴定显示，在科分类水平上，其群落组成与高通量测序数据及其他相关研究中的木材相关细菌群落分类组成高度相似，证实所分离的菌株可代表木材相关细菌群落。