Cellulose is an abundant source of carbon, accounting for more than 50% of foliage and 90% of woody tissues of plants. Despite the diversity of species that include living or dead plant tissue in their diets, the ability to digest cellulose through self-produced enzymatic machinery is considered rare in the animal kingdom. The majority of animals studied to date rely on the cellulolytic activity of symbiotic microorganisms in their digestive tract, with some evidence for a complementary action of endogenous cellulases. Terrestrial isopods have evolved a lifestyle including feeding on a lignocellulose diet. Whether isopods utilize both external and internal cellulases for digestion of a diet is still not understood. We experimentally manipulated the content of cellulose (30%, 60%, or 90%) and the amount of biofilm (small or large) in the offered food source and quantified growth and cellulolytic activity in the gut of the isopod Porcellio scaber. The presence of a visible biofilm significantly promoted isopod growth, regardless of the cellulose content in the diet. The activity of gut cellulases was not significantly affected by the amount of biofilm or the cellulose content. Our results do not support a significant contribution of either ingested or host enzymes to cellulose utilization in P. scaber. Cellulose might not represent a key nutrient for isopods and does not seem to affect the nutritional value of the diet-associated biofilm. We propose that it is the biofilm community that determines the quality of plant diet in terrestrial isopods and potentially also in other detrital plant feeders.

中文翻译：

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生物膜改善了等足动物的生长，而与膳食纤维素含量无关。

纤维素是碳的丰富来源，占植物叶子的50％以上和木质组织的90％以上。尽管饮食中包括活植物或死植物组织的物种多种多样，但在动物界中，人们仍认为通过自身产生的酶促机制消化纤维素的能力很少。迄今为止研究的大多数动物都依赖共生微生物在其消化道中的纤维素分解活性，并且有一些证据表明内源纤维素酶具有互补作用。陆生等足动物已经进化出一种生活方式，包括以木质纤维素饮食为食。异足类动物是否利用外部和内部纤维素酶消化食物仍是未知的。我们通过实验来控制纤维素的含量（30％，60％，（或90％）以及所提供食物来源中生物膜的数量（大小），以及等足类Porcellio scaber肠道中的定量生长和纤维素分解活性。可见的生物膜的存在显着促进了等足动物的生长，而与饮食中的纤维素含量无关。肠纤维素酶的活性不受生物膜量或纤维素含量的显着影响。我们的结果不支持摄入的酶或宿主酶对S. scaber的纤维素利用有重大贡献。纤维素可能不代表等足动物的关键营养素，并且似乎不影响饮食相关生物膜的营养价值。我们建议由生物膜群落来决定陆生等足动物以及其他碎屑植物饲养者中植物饮食的质量。