Date of Award

Winter 2016

Project Type


Program or Major


Degree Name

Master of Science

First Advisor

Louis S Tisa

Second Advisor

Serita Frey

Third Advisor

William K Thomas


The symbiosis between Frankia and actinorhizal plants in the genus Casuarina are intentionally exploited in efforts to reclaim degraded lands and improve agricultural production through the practice of agroforestry, particularly in countries on the continent of Africa. Laboratory investigations have shown that some non-Frankia bacteria isolated from the root nodules of Casuarina plants can play active and positive roles in this symbiosis, but a culture-independent survey of the microbial community in system had not yet been conducted. To fill this knowledge-gap, a metagenomic survey of the endophytic microbial community of Casuarina glauca root nodules was performed at three sites in the country of Tunisia. The sites were chosen to evaluate the difference in community structure across a steep gradient of aridity. To complement this survey, a shotgun metagenomic analysis of the endophytic and epiphytic microbial community of C. glauca root nodules at these sites was also performed. Results of both analyses found a sharp decrease in the abundance of the symbiont Frankia in the semi-arid and arid samples. Other microbial taxa that were known to be active in the system as well as previously unobserved taxa were found in increased abundance in samples with decreased Frankia abundance. These results show a strong effect of climate on the endophytic community associated with C. glauca and provide insights for continued laboratory and field testing of this system.