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

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.

Diversity and Structure of the Endophytic Bacterial Communities Associated With Three Terrestrial Orchid Species as Revealed by 16S rRNA Gene Metabarcoding

“…Because of their importance in the survival of these endangered plants, most of the microbiological investigations on orchids have focused on their mycorrhizal associations, leaving aside the potential role of other microbial partners. Bacterial endophytes in orchids have been mainly investigated in commercially valuable species by isolation after surface sterilization of roots and/or leaves, and many isolates have been found to both increase seed germination and promote plant growth ( Tsavkelova et al, 2007 ; Faria et al, 2013 ; da Silva et al, 2015 ; Gontijo et al, 2018 ; Herrera et al, 2020 ). By contrast, culture-independent approaches have been rarely applied to investigate the endophytic bacteria of orchids, and data are only available for the epiphytic orchids Dendrobium officinale and Dendrobium catenatum ( Yu et al, 2013 ; Li et al, 2017 ).…”

Features of Bacterial Microbiota in the Wild Habitat of Pulsatilla tongkangensis, the Endangered “Long-Sepal Donggang Pasque-Flower Plant,” Endemic to Karst Topography of Korea

“…Most of the strains have been previously reported to be associated with plant growth-promoting activity ( Egamberdieva et al, 2018 ; Afzal et al, 2019 ). For instance, in addition to the well-known plant growth-promoting species of Pseudomonas and Bacillus , Variovorax boronicumulans has been reported to colonize the root tissues of orchids along with mycorrhiza and contribute toward seedling development at early stages ( Herrera et al, 2020 ). The abundance of plant-beneficial bacteria associated with DPF plants might contribute to the survival and establishment of host plants in the natural environment.…”

Mycorrhizal Fungi Isolated from Native Terrestrial Orchids from Region of La Araucanía, Southern Chile

“…Additionally, bacterial endophytes may positively interact to improve the nutrition and growth of mycoheterotrophic species, such as in the case of Arachnitis uniflora and Dendrobium catenatum [39,40]. Associations with such microorganisms are necessary for orchids, especially after the initial mycoheterotrophic stage, for them to become established in the ecosystem [39,41]. Our results showed that, after two months of symbiotic germination, the growing protocorms slow their growth, probably by the lack of appropriated soil-borne fungi able to contribute synergistically to plant growth.…”