Selection and Characterization of Burkholderia spp. for Their Plant-Growth Promoting Effects and Influence on Maize Seed Germination

Isaneli Batista Dos Santos,Júlia Kuklinsky Sobral,João Tiago Correia Oliveira,Elke Jurandy Bran Nogueira Cardoso,Arthur Prudêncio De Araújo Pereira,Maria Carolina Quecine Verdi,Adijailton José De Souza,Flaviana Gonçalves Da Silva

doi:10.3389/fsoil.2021.805094

Abstract

Burkholderia sp. is a bacterial genus extremely versatile in the environment and has been reported for a great potential to promote plant growth via different mechanisms. Here we evaluate the plant growth-promoting mechanisms in twenty-six Burkholderia strains. Strains were evaluated for their ability to promote plant growth by means of: indole-3-acetic acid (IAA) production under different conditions of pH, salt stress and the presence or absence of L-tryptophan; exopolysaccharides (EPS) production and quorum sensing (ALH). The strains were also characterized in terms of their genetic variability and species identification through Sanger sequencing. Then, the bacteria most responsive in the greatest number of plant-growth promotion mechanisms were selected for a corn seed germination test. All bacteria synthesized IAA in medium with 0.0 or 5.0 mM of L-tryptophan in combination with either 1 or 5% of NaCl, and pH values of either 4.5 or 7.2. The EPS production was confirmed for 61.54% of the bacterial strains. Quorum sensing also occurred in 92.3% of the selected bacteria. The Jaccard similarity coefficient revealed 16 clusters with high genetic variability between bacterial strains. Bacterial strains were assigned to seven species: B. anthina, B. cepacia, B. gladioli, B. ambifaria, B. graminis, B. heleia, and Burkholderia spp. The corn seed bacterization did not affect the germination velocity index (GSI), as well as the first count of germinated seeds (FC). However, inoculations formulated with B. heleia strain G28, B. gladioli strain UAGC723, and B. graminis strain UAGC348 promoted significant increases in root length, seedling height and fresh and dry seedling phytomass, respectively. These results indicate the high biotechnological potential of several strains in the genus Burkholderia sp. as seed inoculants, favoring germination and seedling initial development.

Highlights

Plants provide a wide variety of niches for growth and proliferation for a great diversity of microorganisms, including bacteria, fungi, protists, nematodes, and viruses, which make up the plant microbiota [1, 2]
L-tryptophan plays an important role in the indole-3-acetic acid (IAA) biosynthesis, and its presence in the culture medium increases the phytohormone production by the majority of plant growth promoting bacteria (PGPB) [34, 35]
The L-tryptophan eigenvector positively correlated with the bacteria B. cepacia (B2, B3, and B4), B. gladioli (B10 and B22), B. anthina (B5), B. heleia (B24) and Burkholderia spp. (B19 e B20), suggesting their dependency on the same biological pathway to synthesize this phytohormone in vitro (Figure 1)

Summary

Introduction

Plants provide a wide variety of niches for growth and proliferation for a great diversity of microorganisms, including bacteria, fungi, protists, nematodes, and viruses, which make up the plant microbiota [1, 2]. The plantbacteria interaction has been the basis of bioproducts that promote increased productivity of agricultural crops, especially inoculants with mechanisms that promote plant-growth, nutrient acquisition and increases of plant tolerance and resistance to abiotic stresses and pests attack [5,6,7]. Most of these interactions occur in the soil-plant interface using specific niches such as the rhizosphere, endosphere and rhizoplane [1, 2, 8]. The root epiphytic bacteria, which are inhabitants of the root surface (rhizoplane) have a crucial role in stimulating plant development [3, 9]

Methods

Results

Conclusion