The Plant-Associated Flavobacterium: A Hidden Helper for Improving Plant Health

Abstract

Flavobacterium is a genus within the phylum Bacteroidota that remains relatively unexplored. Recent analyses of plant microbiota have identified the phylum Bacteroidota as a major bacterial group in the plant rhizosphere. While Flavobacterium species within the phylum Bacteroidota have been recognized as pathogens in the aquatic habitats, microbiome analysis and the characterization of novel Flavobacterium species have indicated the great diversity and potential of their presence in various environments. Many Flavobacterium species have positively contribute to plant health and development, including growth promotion, disease control, and tolerance to abiotic stress. Despite the well-described beneficial interactions of the Flavobacterium species with plants, the molecular mechanisms and bacterial determinants underlying these interactions remain unclear. To broaden our understanding of the genus Flavobacterium's role in plant health, we review the recent studies focusing on their ecological niche, functional roles, and determinants in plant-beneficial interactions. Additionally, this review discusses putative mechanisms explaining the interactions between plants and Flavobacterium. We have also introduced the importance of future research on Flavobacterium spp. and its potential applications in agriculture.

Keywords: Flavobacterium; plant microbiome; plant-beneficial interactions.

Fig. 1

Composition of the genus Flavobacterium in various ecosystems. (A) The number of Flavobacterium isolates from different habitats, based on data from BacDive (https://bacdive.dsmz.de/). A total of 387 Flavobacterium isolates were obtained from aquatic environments, plants, soil, fish, and other sources. Light blue box, the isolates from aquatic environments; green box, the isolates from plants; light brown box, the isolates from soil; beige box, the isolates from fish; gray box, the isolates from others. (B) Geographic distribution and ecological roles of the genus Flavobacterium. Bacteria of the genus Flavobacterium are primarily found in aquatic environments where they serve various ecological roles. Flavobacterium species act as a pathogen of fish, algicidal organism, and a decomposer of biopolymers. Besides, certain Flavobacterium species contribute to carbon cycling and promote plant health in soil environments. PGPR, plant growth-promoting rhizobacteria.

Fig. 2

An overview of diverse determinants and functional roles within the genus Flavobacterium in plant-beneficial interactions. (A) Volatile organic compounds (VOCs). Bacteria in the genus Flavobacterium release 2,4-Di-tert-butylphenol, which exhibits biological control activity. (B) Nutrient sources. Bacteria in the genus Flavobacterium can provide inorganic nitrogen and solubilized phosphorus for plant growth promotion. They may supply ferric ions to the host plant via the secretion of siderophores. (C) Plant hormones. Plant hormones such as indole acetic acid and abscisic acid produced by Flavobacterium species contribute to plant growth and abiotic stress tolerance. Flavobacterium species secrete determinants (indicated by black arrows) or putative determinants (indicated by black dashed arrows) for plant-beneficial interactions. These various determinants either promote plant health (indicated by red arrows) or inhibit plant pathogens (indicated by red blunt-ended lines). IAA, indole-3-acetic acid; ABA, abscisic acid.