Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8601, Japan.
Sci Rep. 2021 Sep 28;11(1):19208. doi: 10.1038/s41598-021-98733-y.
Symbiotic fungi of wood-inhabiting insects are often considered to aid wood digestion of host insects when the associated fungi can assimilate wood-associated indigestible materials. In most cases, however, the components of wood that are utilized by fungal symbionts remain poorly understood. The lizard beetle Doubledaya bucculenta (Coleoptera, Erotylidae, Languriinae) farms the symbiotic yeast Wickerhamomyces anomalus inside the cavity of host bamboo internodes, which serves as food for larvae. To determine the carbon sources of the internodes serving as nutritional substrates for W. anomalus, we used ion exchange chromatography measurements to analyze free and structural sugar compositions in fresh pith (FP), yeast-cultured pith (YP), and larva-reared pith (LP) of internodes. Glucose and fructose were the major free sugars in FP and markedly decreased in YP and LP. For structural sugars, no sugar significantly decreased in YP or LP compared with FP. Carbon assimilation tests showed that W. anomalus assimilated glucose, mannose, fructose, and sucrose strongly, xylose and cellobiose moderately, and xylan weakly. Elemental analysis revealed that the compositions of carbon, hydrogen, and nitrogen were not significantly different among tissue types. These results suggest that W. anomalus does not consume bamboo-associated indigestible sugars but most free sugars, mainly glucose and fructose, in the pith. Our findings suggest that a symbiont's abilities may not always benefit its host in nature.
与木质部昆虫共生的真菌通常被认为有助于宿主昆虫消化木质部，当相关真菌能够同化木质部中不可消化的物质时。然而，在大多数情况下，真菌共生体利用的木质部成分仍知之甚少。蜥蜴甲虫 Doubledaya bucculenta（鞘翅目，Erotylidae，Languriinae）在宿主竹节的腔室内养殖共生酵母 Wickerhamomyces anomalus，作为幼虫的食物。为了确定作为 W. anomalus 营养基质的节间的碳源，我们使用离子交换色谱测量法分析了新鲜髓心（FP）、酵母培养的髓心（YP）和幼虫饲养的髓心（LP）中的游离糖和结构糖组成。FP 中的主要游离糖是葡萄糖和果糖，在 YP 和 LP 中明显减少。对于结构糖，与 FP 相比，YP 或 LP 中没有明显减少的糖。碳同化测试表明，W. anomalus 强烈同化葡萄糖、甘露糖、果糖和蔗糖，适度同化木糖和纤维二糖，弱同化木聚糖。元素分析表明，组织类型之间的碳、氢和氮组成没有显著差异。这些结果表明，W. anomalus 不消耗竹节相关的不可消化糖，而是消耗髓心中的大多数游离糖，主要是葡萄糖和果糖。我们的发现表明，共生体的能力在自然界中并不总是有益于其宿主。
