Effect of nitrogen utilizing efficiencies on rhizospheric proteolytic bacterial communities of two maize inbred lines

Rhizospheric microbial composition plays an important role in plant growth and nutrient metabolism. Under the effect of root exudates, soil in rhizosphere is different from bulk soil in its microbial composition and functions from bulk soil. Effect of root exudates on microbial communities had been investigated by various researchers, still leaving a gap in study of effect on functions related to soil. One such important soil function is proteolysis. Proteases and peptidases are important enzymes that bring about N mineralization and in turn N uptake to facilitate plant growth and development. Understanding of the relationship between soil microbial communities expressing protease activity and nitrogen in the rhizosphere is still a challenge, due to the difficulties of sampling the rhizosphere microenvironment. This study investigated the interplay of plant nitrogen utilizing efficiency with N mineralization brought about by proteolysis with special focus on bacterial extracellular soil proteases. We studied changes in the biochemical activity and microbial community structure in the rhizosphere of the inbred maize (Zea mais L.) lines Lo5 and T250 characterized by high and low Nitrogen utilizing effeciencies (NUE) using rhizobox experiments. Plants were regularly regularly monitored for the inorganic N (NH4+-N and NO3--N) concentration in the rhizosphere by ion selective electrodes (ISE). At the stage of N depletion soil was sampled from rhizosphere and bulk compartments. Cellular biomass was estimated as a measure of ATP and protease activity was assayed as a measure on caseinate hydrolysis. Soil DNA was extracted and was used for molecular studies. Two bacterial genes coding for alkaline proteases (apr) and neutral protease (npr) were selected for studies. Bacterial gene abundance was measured using qPCR. To study diversity of these genes, amplicons were sequenced by Illumina high-throughput technology. Plant L05 with higher NUE, had shown a significant difference in the rhizospheric and bulk cellular biomass, whereas plant T250 with lower NUE showed no significant differences in the biomass content in rhizosphere and bulk soil. Proteolytic soil potential of plant L05 was found to be higher than that of T250. Furthermore abundance of genes apr and npr and their diversities, as indicated by qPCR and sequencing results respectively were favored by the higher NUE of L05 maize line. Analyses of several million apr and npr amplicons revealed a high diversity of proteases genes in soil and rhizosphere, with many sequences that are still unknown according to current sequences database information.