Pycnoscelus surinamensis cockroach gut microbiota respond consistently to a fungal diet without mirroring those of fungus-farming termites

The gut microbiotas of cockroaches and termites play important roles in the symbiotic digestion of dietary components, such as lignocellulose. Diet has been proposed as a primary determinant of community structure within the gut, acting as a selection force to shape the diversity observed within this “bioreactor”, and as a key factor for the divergence of the termite gut microbiota from the omnivorous cockroach ancestor. The gut microbiota in most termites supports primarily the breakdown of lignocellulose, but the fungus-farming sub-family of higher termites has become similar in gut microbiota to the ancestral omnivorous cockroaches. To assess the importance of a fungus diet as a driver of community structure, we compare community compositions in the guts of experimentally manipulated Pycnoscelus surinamensis cockroaches fed on fungus cultivated by fungus-farming termites. MiSeq amplicon analysis of gut microbiotas from 49 gut samples showed a step-wise gradient pattern in community similarity that correlated with an increase in the proportion of fungal material provided to the cockroaches. Comparison of the taxonomic composition of manipulated communities to that of gut communities of a fungus-feeding termite species showed that although some bacteria OTUs shared by P. surinamensis and the farming termites increased in the guts of cockroaches on a fungal diet, cockroach communities remained distinct from those of termites. These results demonstrate that a fungal diet can play a role in structuring gut community composition, but at the same time exemplifies how original community compositions constrain the magnitude of such change.蜚蠊与白蚁的肠道微生物群在膳食组分（如木质纤维素）的共生消化过程中发挥关键作用。已有研究表明，饮食是肠道群落结构的核心决定因素：它作为选择压力塑造了这一“生物反应器”内的物种多样性，同时也是白蚁肠道微生物群从杂食性蜚蠊祖先分化演化的关键因素。多数白蚁的肠道微生物群主要辅助木质纤维素的降解，但高等白蚁中的培菌亚科类群，其肠道微生物群已与祖先杂食性蜚蠊趋于一致。为评估真菌饮食作为群落结构驱动因子的重要性，本研究对比了经实验干预、以培菌白蚁培育的真菌为食的Pycnoscelus surinamensis的肠道群落组成。对49份肠道样本的MiSeq扩增子测序分析显示，群落相似性呈逐步梯度模式，且与投喂给蜚蠊的真菌物质占比升高呈显著正相关。将实验处理组群落的分类组成与食真菌白蚁物种的肠道群落组成进行对比后发现：尽管在以真菌为食的蜚蠊肠道内，Pycnoscelus surinamensis与培菌白蚁共有的部分细菌操作分类单元（operational taxonomic units，OTUs）丰度有所上升，但蜚蠊的肠道群落组成仍与白蚁群落存在显著差异。本研究结果表明，真菌饮食可在塑造肠道群落组成中发挥作用，但同时也印证了原有群落组成会限制这类改变的幅度。