Differential habitat use and niche partitioning by Pseudomonas species in human homes.

Many species of Pseudomonas have the ability to use a variety of resources and habitats, and as a result Pseudomonas are often characterized as having broad fundamental niches. We questioned whether actual habitat use by Pseudomonas species is equally broad. To do this, we sampled extensively to describe the biogeography of Pseudomonas within the human home, which presents a wide variety of habitats for microbes that live in close proximity to humans but are not part of the human flora, and for microbes that are opportunistic pathogens, such as Pseudomonas aeruginosa. From 960 samples taken in 20 homes, we obtained 163 Pseudomonas isolates. The most prevalent based on identification using the SepsiTest BLAST analysis of 16S rRNA (http://www.sepsitest-blast.de) were Pseudomonas monteilii (42 isolates), Pseudomonas plecoglossicida, Pseudomonas fulva, and P. aeruginosa (approximately 25 each). Of these, all but P. fulva differed in recovery rates among evaluated habitat types (drains, soils, water, internal vertebrate sites, vertebrate skin, inanimate surfaces, and garbage/compost) and all four species also differed in recovery rates among subcategories of habitat types (e.g., types of soils or drains). We also found that at both levels of habitat resolution, each of these six most common species (the four above plus Pseudomonas putida and Pseudomonas oryzihabitans) were over- or under-represented in some habitats relative to their contributions to the total Pseudomonas collected across all habitats. This pattern is consistent with niche partitioning. These results suggest that, whereas Pseudomonas are often characterized as generalists with broad fundamental niches, these species in fact have more restricted realized niches. Furthermore, niche partitioning driven by competition among Pseudomonas species may be contributing to the observed variability in habitat use by Pseudomonas in this system.