Wood degradation by Panaque nigrolineatus, a neotropical catfish: diversity and activity of gastrointestinal tract lignocellulolytic and nitrogen fixing communities

Consuming wood as a primary food source poses many challenges for animals. Rich in non-assimilable carbohydrates, wood digestion requires a high degree of anatomical and physiological specialization by both the host and its microbiome. However, wood comsumption (xylivory) as a dietary strategy to obtain energy has been recorded in a small number of animals including beaver, porcupine, and moose and wood typically accounts for a small fraction of the overall diet in these organisms, or, is limited to the nutrient-rich tissues of the bark and vascular cambium. The paucity of wood-feeding organisms is due to the recalcitrant and nutrient-poor nature of the substrate. Our current understanding of wood feeding is limited to a small number of marine and terrestrial invertebrate systems. In this chapter we focus on the Neotropical catfish, Panaque nigrolineatus, which ingests large quantities of wood as part of its diet. The microbiome of P. nigrolineatus has been shown to include bacterial and fungal communities participating in both lignocellulose degradation and nitrogen fixation that are taxonomically distinct from all other wood-feeding organisms, although the functional capacity of these communities is consistent with those observed in other wood-feeders. This environmentally recruited microbiome allows the gastrointestinal tract microbiome a high degree of flexibility and resilience ideally suited to rapid changes in dietary strategy.