Metagenomics is not enough

Living through multispecies societies: Approaching the microbiome with Imanishi Kinji

Recent research about the microbiome points to a picture in which we, humans, are 'living through' nature, and nature itself is living in us. Our bodies are hosting-and depend on-the multiple species that constitute human microbiota. This article will discuss current research on the microbiome through the ideas of Japanese ecologist Imanishi Kinji (1902-1992). First, some of Imanishi's key ideas regarding the world of living beings and multispecies societies are presented. Second, seven types of relationships concerning the human microbiome, human beings, and the environment are explored. Third, inspired by Imanishi's work, this paper develops the idea of dynamic, porous, and complex multispecies societies in which different living beings or species are codependent on others, including microbiota and human beings.

Predicting a human gut microbiota's response to diet in gnotobiotic mice

The interrelationships between our diets and the structure and operations of our gut microbial communities are poorly understood. A model community of 10 sequenced human gut bacteria was introduced into gnotobiotic mice, and changes in species abundance and microbial gene expression were measured in response to randomized perturbations of four defined ingredients in the host diet. From the responses, we developed a statistical model that predicted over 60% of the variation in species abundance evoked by diet perturbations, and we were able to identify which factors in the diet best explained changes seen for each community member. The approach is generally applicable, as shown by a follow-up study involving diets containing various mixtures of pureed human baby foods.

Quorum sensing in natural environments: emerging views from microbial mats

Much laboratory-based information exists on quorum sensing, a type of bacterial cell-to-cell communication that depends upon exchanges of molecular signals between neighboring cells. However, little is known about how this and other microbial sensing systems operate in nature. Geochemical and biological modifications of signals probably occur in extracellular environments, and these could disrupt intended communication if signals are no longer recognized. However, as we discuss here, signal alterations might result in other outcomes: if a modified signal is able to interact with a different receptor then further environmental information can be gained by the receiving cells. We also postulate that quorum sensing occurs within cell clusters, where signal dispersion might be significantly influenced by extracellular polymers. As a model system to discuss these points we use microbial mats - highly-structured biofilm communities living under sharply-defined, fluctuating geochemical gradients.

Conceptualizing human microbiota: from multicelled organ to ecological community

The microbiota of a typical, healthy human contains 10 times as many cells as the human body and incorporates bacteria, viruses, archea, protozoans, and fungi. This diverse microbiome (the collective genomes of the microbial symbionts that inhabit a human host) is essential for human functioning. We discuss the unstated assumptions and implications of current conceptualizations of human microbiota: (1) a single unit that interacts with the host and the external environment; a multicelled organ; (2) an assemblage of multiple taxa, but considered as a single unit in its interactions with the host; (3) an assemblage of multiple taxa, which each interacts with the host and the environment independently; and (4) a dynamic ecological community consisting of multiple taxa each potentially interacting with each other, the host, and the environment. Each conceptualization leads to different predictions, methodologies, and research strategies.