High-Throughput Quantitative Analysis of the Human Intestinal Microbiota with a Phylogenetic Microarray

Gut microbiota carry out key functions in health and participate in the pathogenesis of a growing number of diseases. The aim of this study was to develop a custom microarray that is able to identify hundreds of intestinal bacterial species. We used the Entrez nucleotide database to compile a data set of bacterial 16S rRNA gene sequences isolated from human intestinal and fecal samples. Identified sequences were clustered into separate phylospecies groups. Representative sequences from each phylospecies were used to develop a microbiota microarray based on the Affymetrix GeneChip platform. The designed microbiota array contains probes to 775 different bacterial phylospecies. In our validation experiments, the array correctly identified genomic DNA from all 15 bacterial species used. Microbiota array has a detection sensitivity of at least 1 pg of genomic DNA and can detect bacteria present at a 0.00025% level of overall sample. Using the developed microarray, fecal samples from two healthy children and two healthy adults were analyzed for bacterial presence. Between 227 and 232 species were detected in fecal samples from children, whereas 191 to 208 species were found in adult stools. The majority of identified phylospecies belonged to the classes Clostridia and Bacteroidetes. The microarray revealed putative differences between the gut microbiota of healthy children and adults: fecal samples from adults had more Clostridia and less Bacteroidetes and Proteobacteria than those from children. A number of other putative differences were found at the genus level.In the healthy adult, there are 10¹¹ to 10¹⁴ bacteria colonizing the intestine. This outnumbers the total tissue cells in the body by at least an order of magnitude. The composition and activity of this complex microbial system (called microbiota or microflora) have a major influence on health and disease (9). Commensal microbiota contribute to the trophic functions of the gut (producing fermentation products and vitamins that can be used by intestinal epithelial cells), stimulate the immune function of the gastrointestinal tract, transform or excrete toxic substances, protect the host against invasion by pathogenic species, and modulate gut motility (28, 36). At the same time, recent research incriminates a dysfunctional cross-talk between the host and the microbiota in the pathogenesis of a growing number of disorders, such as irritable bowel syndrome, inflammatory bowel disease, allergic diseases, and gastrointestinal cancer (28).While the intestine in a newborn contains no microbes, immediately after birth the intestine of the infant is colonized by enterobacteria and enterococci. Gradual changes in microbiota composition occur during childhood, with a general reduction in the number of aerobes and facultative anaerobes and an increase in the populations of obligate anaerobic species (27). It is considered that by 2 years of age the microbiota resembles that of an adult, which is dominated in health and disease by species from only four phyla, Firmicutes (predominantly Clostridia; 50 to 70% total bacterial numbers), Bacteroidetes (10 to 30%), Proteobacteria (up to 10%), and Actinobacteria (up to 5%), with 90% believed to be obligate anaerobes (4, 10, 11, 22).Traditionally, microorganisms were detected in intestinal samples and feces by microscopic, biochemical, or physiological methods, or by culturing on selective nutrient media. However, since most intestinal microbiota species are obligate anaerobes, their isolation and culturing are difficult (21, 38, 42). In recent years, new methods based on the use of microarray technology have been utilized for the characterization of complex microbial communities (18, 32, 41, 43, 47). Microarrays represent an excellent choice for the high-throughput analysis of bacterial populations, because many different probes can be placed on one slide or synthesized on one chip, and samples thus can be tested for the presence of many different species simultaneously. Environmental and clinical samples can be interrogated directly, circumventing any need for culturing, and thus nonculturable species can be reliably detected.Several types of microarrays have been used to date to characterize the composition of microbial communities (47). Community genome arrays are constructed using whole genomic DNA (gDNA) isolated from pure culture strains (46). Functional gene arrays contain genes encoding key enzymes that are involved in various biochemical processes, and they are useful for monitoring physiological changes in microbial communities (14, 45). Phylogenetic oligonucleotide arrays contain probes derived from rRNA sequence information and are ideally suited for the analysis of microbial community composition structure and variance. Different types of phylogenetic arrays have been designed for these purposes (26, 30, 31).A number of projects performed in the last several years focused on sampling the diversity of human microbiota by the cloning and subsequent sequencing of the 16S rRNA genes isolated from gastrointestinal and fecal samples (5, 10, 13, 23, 38). In this project, we have designed, developed, and validated a custom microbiota microarray containing 16S rRNA genes probes to 775 different microbial phylospecies of human intestinal bacteria. We also have tested the applicability of this array to profiling the microbiota populations in fecal samples isolated from two adult and two child volunteers.