Abstract
Fresh vegetables harbour diverse bacterial populations on their surfaces which are important for plant health and growth. Information on epiphytic bacteria is limited to only a few types of vegetables and it is unknown how the lettuce epiphytic bacterial community structure may respond when a probiotic product is added to an aquaponic system. In this study, we evaluated lettuce growth and analysed epiphytic bacterial communities of lettuce based on metabarcoding analysis of the V3-V4 region of the 16S rRNA gene obtained from paired-end Illumina MiSeq reads. The addition of Bacillus probiotics resulted in a significant increase of nitrate and phosphate in the deep-water culture solution, as well as increased vegetative growth of lettuce. Metabarcoding analysis revealed that the most abundant phyla on lettuce leaf surfaces were Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria. The in-depth bacterial composition analysis indicated that genera Chryseobacterium, Bacillus, Pantoea, Pseudoduganella, Flavobacterium, Paludibacter, and Cloacibacterium were dominant in leaf samples obtained from Bacillus-treated systems. Analysis of lettuce epiphytic bacterial communities of the fresh lettuce leaf surfaces also indicated the presence of food-borne pathogens belonging to the Shigella and Aeromonas genera, which were less abundant in the probiotic treated systems. This study provides the first characterization of the epiphytic bacterial community structure and how it can be modulated by the addition of a probiotic mixture to the nutrient solution of aquaponic systems.
Highlights
The above-ground surfaces of plants are colonized by microbial communities that may affect their growth and survival through enhancing nutrient acquisition and tolerance to environmental stress [1,2]
Lettuce shoot fresh weight was 15.3% more in the Bacillus probiotic treated systems when compared to the lettuce harvested from the control systems (Table 1)
The absolute growth rate and height gain were significantly increased in the lettuce grown in the Bacillus probiotic treated aquaponic systems (Table 1)
Summary
The above-ground surfaces of plants are colonized by microbial communities that may affect their growth and survival through enhancing nutrient acquisition and tolerance to environmental stress [1,2]. The phylloplane is inhabited by bacteria, archaea, filamentous fungi, and yeasts [3]. These microorganisms may either be associated with plant surfaces as epiphytes or within plant tissue as endophytes [4]. Epiphytic bacteria may provide specific benefits to plants which include increased stress tolerance [6], nitrogen fixation [7], protection of plants against pathogen infections [8,9], and stimulation of plant growth [10]
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