Kono Mieko, Tanabe Hideyuki, Ohmura Yoshihito, Satta Yoko, Terai Yohey
SOKENDAI (The Graduate University for Advanced Studies), Department of Evolutionary Studies of Biosystems, Shonan Village, Hayama, Kanagawa 240-0193, Japan.
Department of Botany, National Museum of Nature and Science, 4-1-1 Amakubo, Tsukuba, Ibaraki 305-0005, Japan.
Microbiology (Reading). 2017 May;163(5):678-691. doi: 10.1099/mic.0.000461. Epub 2017 May 24.
Recent progress in molecular techniques has begun to alter traditional recognition of lichens as symbiotic organisms comprised of a fungus and photosynthetic partners (green algae and/or cyanobacteria). Diverse organisms, especially various non-photosynthetic bacteria, are now indicated to be integral components of lichen symbiosis. Although lichen-associated bacteria are inferred to have functions that could support the symbiosis, little is known about their physical and nutritional interaction with fungi and algae. In the present study, we identified specific interaction between a lichen-forming alga and a novel bacterium. Trebouxia alga was isolated from a lichen, Usnea hakonensis, and kept as a strain for 8 years. Although no visible bacterial colonies were observed in this culture, high-throughput sequencing of DNA isolated from the culture revealed that the strain is composed of a Trebouxia alga and an Alphaproteobacterium species. In situ hybridization showed that bacterial cells were localized on the surface of the algal cells. Physiological assays revealed that the bacterium was able to use ribitol, glucose and mannitol, all of which are known to exist abundantly in lichens. It was resistant to three antibiotics. Bacteria closely related to this species were also identified in lichen specimens, indicating that U. hakonensis may commonly associate with this group of bacteria. These features of the novel bacterium suggest that it may be involved in carbon cycling of U. hakonensis as a member of lichen symbiosis and less likely to have become associated with the alga after isolation from a lichen.
分子技术的最新进展已开始改变人们对 lichens 作为由真菌和光合伙伴（绿藻和/或蓝细菌）组成的共生生物的传统认识。现在表明，多种生物，尤其是各种非光合细菌，是地衣共生的重要组成部分。尽管据推测与地衣相关的细菌具有支持共生的功能，但对于它们与真菌和藻类的物理及营养相互作用却知之甚少。在本研究中，我们确定了一种地衣形成藻类与一种新型细菌之间的特定相互作用。从地衣 Usnea hakonensis 中分离出 Trebouxia 藻类，并作为菌株保存了 8 年。尽管在这种培养物中未观察到可见的细菌菌落，但对从培养物中分离的 DNA 进行的高通量测序表明，该菌株由 Trebouxia 藻类和一种变形杆菌属物种组成。原位杂交显示细菌细胞定位于藻类细胞表面。生理分析表明，该细菌能够利用核糖醇、葡萄糖和甘露醇，所有这些物质在地衣中都大量存在。它对三种抗生素具有抗性。在 lichen 标本中也鉴定出了与该物种密切相关的细菌，这表明 Usnea hakonensis 可能通常与这组细菌相关联。这种新型细菌的这些特征表明，它可能作为地衣共生的一员参与了 Usnea hakonensis 的碳循环，并且在从地衣中分离后不太可能与藻类相关联。
