Abstract
By shedding light on variation in time as well as in space, long-term biogeographic studies can help us define organisms’ distribution patterns and understand their underlying drivers. Here we examine distributions of Pseudomonas in and around 15 human homes, focusing on the P. putida and P. fluorescens species groups. We describe recovery from 10,941 samples collected during up to 8 visits per home, occurring on average 2.6 times per year. We collected a mean of 141 samples per visit, from sites in most rooms of the house, from the surrounding yards, and from human and pet occupants. We recovered Pseudomonas in 9.7% of samples, with the majority of isolates being from the P. putida and P. fluorescens species groups (approximately 62% and 23% of Pseudomonas samples recovered respectively). Although representatives of both groups were recovered from every season, every house, and every type of environment sampled, recovery was highly variable across houses and samplings. Whereas recovery of P. putida group was higher in summer and fall than in winter and spring, P. fluorescens group isolates were most often recovered in spring. P. putida group recovery from soils was substantially higher than its recovery from all other environment types, while higher P. fluorescens group recovery from soils than from other sites was much less pronounced. Both species groups were recovered from skin and upper respiratory tract samples from healthy humans and pets, although this occurred infrequently. This study indicates that even species that are able to survive under a broad range of conditions can be rare and variable in their distributions in space and in time. For such groups, determining patterns and causes of stochastic and seasonal variability may be more important for understanding the processes driving their biogeography than the identity of the types of environments in which they can be found.
Highlights
The distributions of many organisms vary in time as well as space
Because preliminary analyses of recovery of both P. putida group and P. fluorescens group recovery did not differ between these two types of houses, the two types of houses were combined for the analyses presented here, and sites that are specific to homes with people with cystic fibrosis (CF) were removed from the dataset
Twenty-two samples from which more than one morphologically distinguishable colony types were collected yielded isolates from two different species groups, resulting in a total of 1,078 clearly distinct Pseudomonas isolates in our collection. Of these 62% were from the P. putida group and 23% were from the P. fluorescens group
Summary
The distributions of many organisms vary in time as well as space. In microbial ecology and biogeography, studies that include the longitudinal sampling required to address temporal variation have found significant seasonal variation in communities of soils, [1, 2], rhizospheres [3], lakes [4] oceans [5], and even in the indoor built environment [6,7,8,9]. We focus here on two large species groups within the genus Pseudomonas, the P. putida and P. fluorescens groups [12]. Representatives from these groups have been isolated from a variety of habitats such as: soils and rhizospheres [13,14,15], drains[14], fresh and salt water [16,17,18,19,20], plants [21, 22], and in clinical settings [23,24,25]. In a previous study in which we used a similar sampling approach to that described here, we found P. putida group strains to be more common than P. fluorescens group strains in household sites [14]; Igbinosa et al [20] found more P. putida than P. fluorescens in their freshwater and wastewater samplings; and Negi et al [15] isolated substantially more P. fluorescens than P. putida in their collection of cold tolerant Himalayan rhizosphere Pseudomonas strains
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