Root-Derived Endophytic Diazotrophic Bacteria Pantoea cypripedii AF1 and Kosakonia arachidis EF1 Promote Nitrogen Assimilation and Growth in Sugarcane.

Rajesh Kumar Singh,Prakash Lakshmanan,Mukesh Kumar Malviya,Xiu-Peng Song,Anjney Sharma,Yang-Rui Li,Dao-Jun Guo,Pratiksha Singh,Dong-Ping Li,Xiang Li,Krishan K Verma,Li-Tao Yang

doi:10.3389/fmicb.2021.774707

Abstract

Excessive, long-term application of chemical fertilizers in sugarcane crops disrupts soil microbial flora and causes environmental pollution and yield decline. The role of endophytic bacteria in improving crop production is now well-documented. In this study, we have isolated and identified several endophytic bacterial strains from the root tissues of five sugarcane species. Among them, eleven Gram-negative isolates were selected and screened for plant growth-promoting characteristics, i.e., production of siderophores, indole-3-acetic acid (IAA), ammonia, hydrogen cyanide (HCN), and hydrolytic enzymes, phosphorus solubilization, antifungal activity against plant pathogens, nitrogen-fixation, 1-aminocyclopropane-1-carboxylic acid deaminase activity, and improving tolerance to different abiotic stresses. These isolates had nifH (11 isolates), acdS (8 isolates), and HCN (11 isolates) genes involved in N-fixation, stress tolerance, and pathogen biocontrol, respectively. Two isolates Pantoea cypripedii AF1and Kosakonia arachidis EF1 were the most potent strains and they colonized and grew in sugarcane plants. Both strains readily colonized the leading Chinese sugarcane variety GT42 and significantly increased the activity of nitrogen assimilation enzymes (glutamine synthetase, NADH glutamate dehydrogenase, and nitrate reductase), chitinase, and endo-glucanase and the content of phytohormones gibberellic acid, indole-3-acetic acid, and abscisic acid. The gene expression analysis of GT42 inoculated with isolates of P. cypripedii AF1 or K. arachidis EF1 showed increased activity of nifH and nitrogen assimilation genes. Also, the inoculated diazotrophs significantly increased plant nitrogen content, which was corroborated by the 15N isotope dilution analysis. Collectively, these findings suggest that P. cypripedii and K. arachidis are beneficial endophytes that could be used as a biofertilizer to improve plant nitrogen nutrition and growth of sugarcane. To the best of our knowledge, this is the first report of sugarcane growth enhancement and nitrogen fixation by Gram-negative sugarcane root-associated endophytic bacteria P. cypripedii and K. arachidis. These strains have the potential to be utilized as sugarcane biofertilizers, thus reducing nitrogen fertilizer use and improving disease management.

Highlights

Global food security is a major sustainable development goal of United Nations
Considering the widespread occurrence of diseases and the large reduction in N input required in sugarcane crops in China, we studied the disease control and biological N fixation (BNF) properties of members of The primer sequences shown in Supplementary Table 2 were Pantoea and Kosakonia genera, and the results are presented here. used for the amplification of nifH (Poly et al, 2001), acdS (Li et al, 2011), and Hydrogen cyanide (HCN) (Ramette et al, 2003) for all selected strains
A total of 175 endophytic bacterial strains were isolated from the roots of five sugarcane species Among these, only 11 Gramnegative strains of two genera Pantoea and Kosakonia were selected based on partial sequencing of the 16S rRNA gene

Summary

Introduction

Global food security is a major sustainable development goal of United Nations. This is a major challenge for developing countries with limited resources and scientific capacity. Sustainable intensification of agriculture is a well-recognized concept and is being practiced in the developed world (Tilman et al, 2002; Vanlauwe et al, 2019) It improves resource use efficiency, reduces agricultural inputs, especially fertilizers and other agrichemicals, and expansion of mechanized farm operations. In this context, considerable research to understand and exploit soil and rhizosphere microbiomes and plant endophytes to reduce fertilizer input and suppress pathogens are underway globally. Considerable research to understand and exploit soil and rhizosphere microbiomes and plant endophytes to reduce fertilizer input and suppress pathogens are underway globally This is relevant when 60–90% of the applied chemical fertilizers are wasted depending on the crop and region, and the manufacturing of agri-chemicals like nitrogen (N) fertilizers is a highly energy-intensive process (Bhardwaj et al, 2014). Biofertilizers, which are live cells of microbes, are a potential alternative to chemical fertilizers since they provide nutrients to plants, reduce soil-borne diseases, and improve the health and quality of soil (Bhardwaj et al, 2014; Kour et al, 2020)

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Conclusion