Viruses Outnumbered Microbes in Abundance in Rhizosphere of Zea mays Genotype B73 and Close Relative Zea mays subsp. parviglumis

Abstract:

Viruses are the most abundant biological entity on Earth from aquatic systems to soils and are present wherever living cells are found. Within soil environments, plant roots create an environment where microorganisms thrive by releasing root exudates. Insight into virus interactions in the rhizosphere abundance can enhance our understanding about viral induced bacterial mortality. Abundance of cells and viruses in rhizo-microbiome was investigated using, biological replicates of Zea mays genotype B73 and Zea mays subsp. parviglumis. Plants were cultivated in greenhouse over a period of 21 days until a growth stage of V4-V8 and then placed in controlled atmosphere chambers for a pulse of 420 ppm CO₂. Following the pulse, plants were removed from chambers and harvested after 8 hours. The plant and root phenotypic traits including total leaf surface area, total leaf fresh weight and dry weight, total root surface area, total root volume, total root density and total root biomass were collected. Cell and virus samples were collected from the root rhizosphere and rhizoplane by sonication followed by centrifugation at 800 x g and immediate filtration through 0.45 µm membrane and collected on a 0.2 µm membrane for cell samples and 0.2 µm membrane and collected on a 0.02 µm Anodisc membrane for virus samples. Enumeration revealed that average cell abundance for Zea mays genotype B73 and Zea mays subsp. parviglumis was (1.54 ± 0.16) x 10⁷ g^-1 and (1.34 ± 0.30) x 10⁷ g^-1 of rhizosphere respectively with no statistically significant difference. Similarly, average virus abundance was in Zea mays genotype B73 and Zea mays subsp. parviglumis was (2.28 ± 0.20) x 10⁷ g^-1 and (2.89 ± 0.55) x 10⁷ g^-1 of rhizosphere respectively with not a significant difference. While, cells and virus abundance between the two species was not statistically different, virus to cell ratio (VCR) for per gram of rhizosphere of Zea mays genotype B73 (VCR = 1.52 ± 0.12) and Zea mays subsp. parviglumis (VCR = 2.24 ± 0.21) was statistically different. Together, these results indicate variations of microbe-virus interactions in the rhizosphere of Zea mays genotype B73 and Zea mays subsp. parviglumis as well reveal a dynamic of viral interactions in the rhizosphere which has the potential to alter microbial community structure and function.