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Front. Microbiol. | doi: 10.3389/fmicb.2018.02710

Putative Nitrogen-fixing bacteria Associated with The Rhizosphere and Root Endosphere of wheat plants grown in an Andisol from southern Chile

  • 1Department of Chemical Sciences and Natural Resources, University of La Frontera, Chile
  • 2Center of Plant, Soil Interaction and Natural Resources Biotechnology, Scientific and Technological Bioresource Nucleus, Chile
  • 3Programa de Doctorado en Ciencias de Recursos Naturales, Universidad de La Frontera, Chile
  • 4University of Minnesota BioTechnology Institute, United States
  • 5Department of Plant and Microbial Biology, University of Minnesota, United States
  • 6Department of Soil, Water and Climate, University of Minnesota, United States

Acidic ash derived volcanic soils (Andisols) support 50% of cereal production in Chile. Nitrogen (N) is essential for cereal crops and commonly added as urea with consequent environmental concerns due to leaching. Despite the relevance of N to plant growth, few studies have focused on understanding the application, management and ecological role of N2-fixing bacterial populations as tool for improve the N nutrition of cereal crops in Chile. It is known that N2-fixing bacteria commonly inhabits diverse plant compartments (e.g., rhizosphere and root endosphere) where they can supply N for plant growth. Here, we used culture-independent and dependent approaches to characterize and compare the putative N2-fixing bacteria associated with the rhizosphere and root endosphere of wheat plants grown in an Andisol from southern Chile. Our results showed significantly greater bacterial loads in the rhizosphere than the root endosphere. Quantitative PCR results indicated that the copy number of the 16S rRNA gene ranged from 10^12~10^13 and 10^7~10^8 g-1 sample in rhizosphere and root endosphere, respectively. The nifH gene copy number ranged from 10^5~10^6 and 10^5 g-1 sample in rhizosphere and root endosphere, respectively. The total culturable bacteria number ranged from 10^9~10^10 and 10^7~10^8 CFU g-1 sample in rhizosphere and 10^4~10^5 and 10^4 CFU g-1 sample in root endosphere using LB and NM-1 media, respectively. Indirect counts of putative N2-fixing bacteria were 10^3 and 10^2~10^3 CFU g-1 sample in rhizosphere and root endosphere using NFb medium, respectively. Sequencing of 16S rRNA genes from randomly selected putative N2-fixing bacteria revealed the presence of members of Proteobacteria (Bosea and Roseomonas), Actinobacteria (Georgenia, Mycobacterium, Microbacterium, Leifsonia and Arthrobacter), Bacteroidetes (Chitinophaga) and Firmicutes (Bacillus and Psychrobacillus) taxa. Differences in 16S rRNA and putative nifH-containing bacterial communities between rhizosphere and root endosphere were shown by denaturing gradient gel electrophoresis (DGGE). This study shows a compartmentalization between rhizosphere and root endosphere for both the abundance and diversity of total (16S rRNA) and putative N2-fixing bacterial communities on wheat plants grown in Chilean Andisols. This information can be relevant for the design and application of agronomic strategies to enhance sustainable N-utilization in cereal crops in Chile.

Keywords: Andisol, root endosphere, N2-fixing bacteria, rhizosphere, wheat

Received: 26 Jun 2018; Accepted: 23 Oct 2018.

Edited by:

Benjamin Gourion, UMR2594 Plant Interactions Laboratory Microorganisms (LIPM), France

Reviewed by:

Feth-el-Zahar Haichar, Microbial Ecology, France
Andrzej Tkacz, University of Oxford, United Kingdom  

Copyright: © 2018 Rilling, Acuña, Sadowsky and Jorquera. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence:
Mr. Joaquin I. Rilling, Department of Chemical Sciences and Natural Resources, University of La Frontera, Temuco, Chile, j.rilling01@ufromail.cl
Dr. Milko A. Jorquera, Department of Chemical Sciences and Natural Resources, University of La Frontera, Temuco, Chile, milko.jorquera@ufrontera.cl