Isolation and Identification of Endophytic Bacteria from Mycorrhizal Tissues of Terrestrial Orchids from Southern Chile

Héctor Herrera,Trevor C Charles,Alžběta Novotná,Tedy Sanhueza,Cesar Arriagada

doi:10.3390/d12020055

Abstract

Endophytic bacteria are relevant symbionts that contribute to plant growth and development. However, the diversity of bacteria associated with the roots of terrestrial orchids colonizing Andean ecosystems is limited. This study identifies and examines the capabilities of endophytic bacteria associated with peloton-containing roots of six terrestrial orchid species from southern Chile. To achieve our goals, we placed superficially disinfected root fragments harboring pelotons on oatmeal agar (OMA) with no antibiotic addition and cultured them until the bacteria appeared. Subsequently, they were purified and identified using molecular tools and examined for plant growth metabolites production and antifungal activity. In total, 168 bacterial strains were isolated and assigned to 8 OTUs. The orders Pseudomonadales, Burkholderiales, and Xanthomonadales of phylum Proteobacteria were the most frequent. The orders Bacillales and Flavobacteriales of the phylla Firmicutes and Bacteroidetes were also obtained. Phosphate solubilization was detected in majority of isolates; however, it was significantly higher in Collimonas pratensis and Chryseobacterium sp. (PSI = 1.505 ± 0.09 and 1.405 ± 0.24, respectively). Siderophore production was recorded only for C. pratensis (0.657 ± 0.14 mm day−1), Dyella marensis (0.131 ± 0.02 mm day−1), and Luteibacter rhizovicinus (0.343 ± 0.12 mm day−1). Indole acetic acid production was highly influenced by the isolate identity; however, the significantly higher activity was recorded for Pseudomonas spp. (ranging from 5.507 ± 1.57 µg mL−1 to 7.437 ± 0.99 µg mL−1). Additionally, six bacterial isolates were able to inhibit the growth of some potential plant pathogenic fungi. Our findings demonstrate the potential for plant growth promoting capabilities and some antifungal activities of endophytic bacteria inhabiting the mycorrhizal tissue of terrestrial orchids, which may contribute especially at early developmental stages of orchid seedlings.

Highlights

Plant endophytes cover a broad spectrum of microorganisms with beneficial, neutral, or detrimental effects on plant growth and development [1]
Our findings demonstrate the potential for plant growth promoting capabilities and some antifungal activities of endophytic bacteria inhabiting the mycorrhizal tissue of terrestrial orchids, which may contribute especially at early developmental stages of orchid seedlings
C. magellanica, accounting 40 bacterial colonies (Figure 1); (v) five bacterial strains were isolated from Gavilea araucana, accounting 31 bacterial colonies (Figure 1); and (vi) eight bacterial strains were isolated from G. lutea, accounting

Summary

Introduction

Plant endophytes cover a broad spectrum of microorganisms with beneficial, neutral, or detrimental effects on plant growth and development [1]. Plant growth-promoting bacteria (PGPB) were first mentioned and examined by Kloepper and Schroth [7]. PGPB are primarily soil microorganisms living in close vicinity of plant roots (rhizosphere) under the direct influence of the root exudates [8]. The bacteria colonize the root cortical cells and establish a symbiotic relationship with the plant host [9]. The bacteria are one of the most common soil microorganisms [6], only a very limited number of them can be cultivated under laboratory conditions in order to examine their beneficial capabilities [10,11]

Methods

Results

Discussion

Conclusion