North Central Agricultural Research Laboratory, United States Department of Agriculture-Agricultural Research Service, Brookings, South Dakota, USA.
PLoS One. 2010 May 26;5(5):e10831. doi: 10.1371/journal.pone.0010831.
Obligate bacterial symbionts alter the diets of host animals in numerous ways, but the ecological roles of facultative bacterial residents that colonize insect guts remain unclear. Carabid beetles are a common group of beneficial insects appreciated for their ability to consume insect prey and seeds, but the contributions of microbes to diet diversification in this and similar groups of facultative granivores are largely unknown.
Using 16S rRNA gene clone libraries and terminal restriction fragment (tRF) length polymorphism analyses of these genes, we examined the bacterial communities within the guts of facultatively granivorous, adult Harpalus pensylvanicus (Carabidae), fed one of five dietary treatments: 1) an untreated Field population, 2) Seeds with antibiotics (seeds were from Chenopodium album), 3) Seeds without antibiotics, 4) Prey with antibiotics (prey were Acheta domesticus eggs), and 5) Prey without antibiotics. The number of seeds and prey consumed by each beetle were recorded following treatment. Harpalus pensylvanicus possessed a fairly simple gut community of approximately 3-4 bacterial operational taxonomic units (OTU) per beetle that were affiliated with the Gammaproteobacteria, Bacilli, Alphaproteobacteria, and Mollicutes. Bacterial communities of the host varied among the diet and antibiotic treatments. The field population and beetles fed seeds without antibiotics had the closest matching bacterial communities, and the communities in the beetles fed antibiotics were more closely related to each other than to those of the beetles that did not receive antibiotics. Antibiotics reduced and altered the bacterial communities found in the beetle guts. Moreover, beetles fed antibiotics ate fewer seeds, and those beetles that harbored the bacterium Enterococcus faecalis consumed more seeds on average than those lacking this symbiont.
CONCLUSIONS/SIGNIFICANCE: We conclude that the relationships between the bacterium E. faecalis and this factultative granivore's ability to consume seeds merit further investigation, and that facultative associations with symbiotic bacteria have important implications for the nutritional ecology of their hosts.
专性细菌共生体以多种方式改变宿主动物的饮食，但定植于昆虫肠道的兼性细菌居民的生态角色仍不清楚。步行甲是一类常见的有益昆虫，以其捕食昆虫猎物和种子的能力而受到赞赏，但微生物对这类兼性食谷者和其他类似群体饮食多样化的贡献在很大程度上仍是未知的。
使用 16S rRNA 基因克隆文库和这些基因的末端限制性片段（tRF）长度多态性分析，我们研究了兼性食谷、成年 Harpalus pensylvanicus（步甲科）肠道内的细菌群落，这些甲虫接受了以下五种饮食处理之一：1）未处理的野外种群，2）带抗生素的种子（种子来自藜），3）不带抗生素的种子，4）带抗生素的猎物（猎物是家蟋蟀的卵），5）不带抗生素的猎物。处理后记录每只甲虫消耗的种子和猎物的数量。Harpalus pensylvanicus 的肠道群落相对简单，每个甲虫大约有 3-4 个细菌操作分类单元（OTU），这些 OTU 与γ变形菌、芽孢杆菌、α变形菌和柔膜菌有关。宿主的细菌群落因饮食和抗生素处理而不同。野外种群和未喂食抗生素的种子的甲虫具有最接近的匹配细菌群落，而喂食抗生素的甲虫的群落彼此之间比未喂食抗生素的甲虫的群落更为相似。抗生素减少并改变了甲虫肠道中的细菌群落。此外，喂食抗生素的甲虫吃的种子较少，而那些携带肠球菌（Enterococcus faecalis）的甲虫平均比缺乏这种共生体的甲虫消耗更多的种子。
结论/意义：我们的结论是，肠球菌（Enterococcus faecalis）与这种兼性食谷者消耗种子的能力之间的关系值得进一步研究，并且与共生细菌的兼性关联对其宿主的营养生态学具有重要意义。
