First Steps into Ruminal Microbiota Robustness

SIMPLE SUMMARY: Microbial fermentation in the rumen is of central importance with respect to ruminant nutrition, as it provides energy and protein to meet animal requirements. The development of high-throughput sequencing techniques has provided an opportunity to appreciate that rumen microbial community is very diverse, making it difficult to define its normal status; alternatively, the concept of robustness, understood as the ability of a community to cope with disturbances, has been proposed as a marker of a healthy microbiota. The aim of the present review is to define the concept of microbial community robustness, with special focus on ruminal microbiota, and to describe its potential drivers. The robustness of the microbiota depends on its resistance, resilience and functional redundancy and is enhanced by increased alpha diversity and network complexity. Diverse feeding practices can shape the microbial community in the rumen and ultimately affect its robustness; a high-forage diet seems to be the most reliable strategy to increase both alpha diversity and network complexity and to improve robustness. Additional research should be conducted to confirm the link between microbial community robustness in the rumen and animal health and to elucidate the practical benefits of building a robust rumen. ABSTRACT: Despite its central role in ruminant nutrition, little is known about ruminal microbiota robustness, which is understood as the ability of the microbiota to cope with disturbances. The aim of the present review is to offer a comprehensive description of microbial robustness, as well as its potential drivers, with special focus on ruminal microbiota. First, we provide a briefing on the current knowledge about ruminal microbiota. Second, we define the concept of disturbance (any discrete event that disrupts the structure of a community and changes either the resource availability or the physical environment). Third, we discuss community resistance (the ability to remain unchanged in the face of a disturbance), resilience (the ability to return to the initial structure following a disturbance) and functional redundancy (the ability to maintain or recover initial function despite compositional changes), all of which are considered to be key properties of robust microbial communities. Then, we provide an overview of the currently available methodologies to assess community robustness, as well as its drivers (microbial diversity and network complexity) and its potential modulation through diet. Finally, we propose future lines of research on ruminal microbiota robustness.