Abstract
The aim of the study was to determine the still not completely described microbiome associated with the aquatic fern Azolla filiculoides. During the experiment, 58 microbial isolates (43 epiphytes and 15 endophytes) with different morphologies were obtained. We successfully identified 85% of microorganisms and assigned them to 9 bacterial genera: Achromobacter, Bacillus, Microbacterium, Delftia, Agrobacterium, and Alcaligenes (epiphytes) as well as Bacillus, Staphylococcus, Micrococcus, and Acinetobacter (endophytes). We also studied an A. filiculoides cyanobiont originally classified as Anabaena azollae; however, the analysis of its morphological traits suggests that this should be renamed as Trichormus azollae. Finally, the potential of the representatives of the identified microbial genera to synthesize plant growth-promoting substances such as indole-3-acetic acid (IAA), cellulase and protease enzymes, siderophores and phosphorus (P) and their potential of utilization thereof were checked. Delftia sp. AzoEpi7 was the only one from all the identified genera exhibiting the ability to synthesize all the studied growth promoters; thus, it was recommended as the most beneficial bacteria in the studied microbiome. The other three potentially advantageous isolates (Micrococcus sp. AzoEndo14, Agrobacterium sp. AzoEpi25 and Bacillus sp. AzoEndo3) displayed 5 parameters: IAA (excluding Bacillus sp. AzoEndo3), cellulase, protease, siderophores (excluding Micrococcus sp. AzoEndo14), as well as mineralization and solubilization of P (excluding Agrobacterium sp. AzoEpi25).
Highlights
Plants and microorganisms form complex associations displaying diverse interactions ranging from mutualism to pathogenicity
These beneficial microorganisms are termed as Plant Growth-Promoting Bacteria (PGPB) [3,5]
We found only one paper describing the capability of A. filiculoides and A. pinnata endosymbiotic Arthrobacter sp. for indole-3-acetic acid (IAA) production, where the auxin concentration remained at the level of 1.5–10 μg mL−1 at an L-tryptophan dose of 100–600 μg·mL−1 [30]
Summary
Plants and microorganisms form complex associations displaying diverse interactions ranging from mutualism to pathogenicity. Given the co-evolution process between plants and their associated microbiome resulting in a strong genomic interdependency, plants and their microbiome are considered as a metaorganism or a holobiont [4]. Plant-associated microbes, especially endophytes, play a crucial role in plant growth and development, allowing them to survive harsh conditions [1], which is important for food production (increased crops, biocontrol of plant diseases) and for coping with contaminants (phytoremediation). These beneficial microorganisms are termed as Plant Growth-Promoting Bacteria (PGPB) [3,5]
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