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Microbial Diversity in Sonoran Desert Soils


The trainees of the NSF-funded IGERT Program in Comparative Genomics at the University of Arizona found that microbial communities are extremely abundant and diverse in the soils of the Sonoran Desert. They also discovered that microbial communities are primarily shaped by soil characteristics associated with geographic location. In contrast, previous studies suggested that microbial diversity at a local level is primarily driven by plant associations and by soil characteristics. For example, in nutrient-poor desert soils, plants have been known to influence soil microbial populations. The trainees surveyed microbial diversity using “next-generation” sequencing technology and determined the relative influence of location, soil properties, and plant associations on the microbial communities. Their project focused on two closely related cacti, the saguaro and the cardon, from three different locations – two natural locations and one man-made location (Biosphere 2). For each location, they sampled soil near cacti and in the rhizosphere, the region of soil where microbial communities are directly influenced by the root system. By using high-throughput, culture independent surveys of the microbial communities, the trainees were able to identify more species of bacteria and archaea than previously found using culturing techniques.

According to the resource-island hypothesis, in a nutrient-limited environment such as a desert, the microbial diversity should be greater in the rhizosphere than in the surrounding soil. However, the trainees found no difference in the abundance or diversity of microbes in the surrounding soil compared to the rhizosphere. Instead they found that geographic location was the primary driving force for diversity. Both pH and the amount of carbon were significantly related to the diversity of microbes. Interestingly, neither nitrogen nor water content was correlated with microbial diversity. This project was developed two years ago in the IGERT Program’s required course, “Problems in Genomics” and illustrates the power of modern genomic techniques. The trainees have recently submitted a manuscript to the journal Applied Environmental Microbiology. This interdisciplinary training program brought together students from a wide range of departments (Neuroscience, Molecular and Cellular Biology, Insect Science, Genetics, and Natural Resources) to work together on a single research project.

Address Goals

This research addresses our primary goal by advancing our knowledge of microbial communities in the soil with potential implications for human health (Valley Fever, for example, is caused by a fungus commonly found in the desert soils in the Southwest). This project addresses our second goal by educating the scientific community about different techniques and their applications. Also, the trainees acquired new skills and learned how to work in a group of people with diverse backgrounds. By doing so, these trainees are helping build a broad, interactive, and interdisciplinary scientific community.