Abstract

Phosphorus is a necessary macronutrient for crop growth and is often added to agricultural fields to increase productivity, but excess phosphorous runoff creates ecological problems in the form of eutrophic microbial blooms in soil or water. The growth rate hypothesis suggests that rapidly growing organisms have a higher phosphorous demand because ribosomal RNA necessary for protein synthesis and is also relatively phosphorus rich compared to other biomolecules. Ribosomal RNA sequence and structure is highly conserved across all organisms, but it exists in multiple tandem copies that vary in number between species. The objective of this study is to test the hypothesis that the number of 18s rRNA copies in a genome is positively correlated with growth rate in bacterial-feeding nematodes. To accomplish this, nematodes were isolated from varying soil samples and identified by morphology and 18S sequence. Growth rate was quantified as reproductive output, generation time, and intrinsic rate by constructing life history tables from growth experiments for each species identified. Ribosomal copy number was determined by quantitative polymerase chain reaction (qPCR) of 18s rRNA against a known single-copy gene (RNA polymerase II). Copy number estimates ranged from 37 to 411, but preliminary results fail to indicate a clear association between growth rate and 18s rRNA copy number. This research will 1) provide helpful copy number correction factors for use with high-throughput amplicon sequencing, 2) aid in understanding why rRNA occurs in multiple tandem copies of varying numbers, and 3) help to understand the phosphorus cycle and how nutrient enrichment shapes microbial community composition.