Microbial Communities of Ascocarps and Soils in a Natural Habitat of Tuber Indicum

Truffles are the fruiting bodies of hypogeous fungi in the genus Tuber. Some truffle species usually grow in an area devoid of vegetation, called brûlé, which knowledge about the microbial composition and structure is still limited. Here, we investigated the bacterial and fungal communities of Tuber indicum ascocarps and soils inside and outside a characteristic brûlé from a poplar plantation with no truffle production history in northeastern China using a high-throughput sequencing approach. A predominance of bacterial phylum Proteobacteria was observed in all samples, with Bacillus among the main genera in the ascocarps, while members of Lysobacter and unidentified Acidobacteria were more abundant in the soil. In addition, Gibberella, Fusarium and Absidia were the dominant fungi in the ascocarps, while Tuber were enriched in the ascocarps and soils inside the brûlé. Soil samples from inside the brûlé had a lower bacterial diversity and a greater fungal diversity than did those from outside the brûlé. Furthermore, some mycorrhization helper bacteria (Rhizobium) and ectomycorrhiza-associated bacteria (Lysobacter) were detected, indicating their potential roles in the complex development of underground fruiting bodies and brûlé formation. These findings may contribute to the protection and cultivation of truffles.

Orchid Root Associated Bacteria: Linchpins or Accessories?

Besides the plant-fungus symbiosis in arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) plants, many endorhizal and rhizosphere bacteria (Root Associated Bacteria, or RAB) also enhance plant fitness, diversity, and coexistence among plants via bi- or tripartite interactions with plant hosts and mycorrhizal fungi. Assuming that bacterial associations are just as important for the obligate mycorrhizal plant family Orchidaceae, surprisingly little is known about the RAB associated with orchids. Herein, we first present the current, underwhelming state of RAB research including their interactions with fungi and the influence of holobionts on plant fitness. We then delineate the need for novel investigations specifically in orchid RAB ecology, and sketch out questions and hypotheses which, when addressed, will advance plant-microbial ecology. We specifically discuss the potential effects of beneficial RAB on orchids as: (1) Plant Growth Promoting Rhizobacteria (PGPR), (2) Mycorrhization Helper Bacteria (MHB), and (3) constituents of an orchid holobiont. We further posit that a hologenomic view should be considered as a framework for addressing co-evolution of the plant host, their obligate Orchid Mycorrhizal Fungi (OMF), and orchid RAB. We conclude by discussing implications of the suggested research for conservation of orchids, their microbial partners, and their collective habitats.