Influence of seasonal changes and salinity on spinach phyllosphere bacterial functional assemblage

Authors: Ibekwe, Abasiofiok - Mark; ORS, SELDA - Ataturk University; Ferreira, Jorge; Liu, Xuan; Suarez, Donald

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2021
Publication Date: 6/1/2021
Citation: Ibekwe, A.M., Ors, S., Ferreira, J.F., Liu, X., Suarez, D.L. 2021. Influence of seasonal changes and salinity on spinach phyllosphere bacterial functional assemblage. PLoS ONE. 16(6). Article e0252242. https://doi.org/10.1371/journal.pone.0252242.
DOI: https://doi.org/10.1371/journal.pone.0252242

Interpretive Summary: The phyllosphere or leaf surface of spinach is the aerial part of the plants that may be consumed by human either fresh or with minimal cooking. It is also the primary center of photosynthetic activities, and consists of one of the most prevalent microbial habitats on plants. In this study, we examined changes in microbial community on spinach leaves due to increasing temperature at harvest. We found that the number of bacterial sequences were higher on leaf surfaces from the early summer planting season in comparison to those from the early winter planting. We also found that some potential human and plant pathogen sequences were least abundant in June as compared to March and May. Therefore, care must be taken in leafy green production management to avoid the critical period of higher population density of potential human pathogen. The results of this research will be used by water quality managers from different water districts, researchers, International Water Management Institute, EPA, and other local agencies that are involved in irrigation management in southwestern United States and other semi-arid regions of the world.

Technical Abstract: The phyllosphere is the aerial part of plants that is exposed to different environmental conditions and is also known to harbor a wide variety of bacteria including both plant and human pathogens. However, studies on phyllosphere bacterial communities have focused on bacterial composition at different stages of plant growth without correlating their functional capabilities to bacterial communities. In this study, we examined the seasonal effects and temporal variabilities driving bacterial community composition and function in spinach phyllosphere due to increasing salinity and season and estimated the functional capacity of bacterial community16S V4 rRNA gene profiles by indirectly inferring the abundance of functional genes based on metagenomics inference tool Piphillin. The experimental design involved three sets of spinach (Spinacia oleracea L., cv. Racoon) grown with saline water during different seasons. Total bacteria DNA from leaf surfaces were sequenced using MiSeq® Illumina platform. About 66.35% of bacteria detected in the phyllosphere were dominated by four phyla- Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria. Permutational analysis of variance (PERMANOVA) showed that phyllosphere microbiomes were significantly (P < 0.003) affected by season, but not salinity (P = 0.501). The most abundant inferred functional pathways in leaf samples were the amino acids biosynthesis, ABC transporters, ribosome, aminoacyl-tRNA biosynthesis, two-component system, carbon metabolism, purine metabolism, and pyrimidine metabolism. The photosynthesis antenna proteins pathway was significantly enriched in June leaf samples, when compared to March and May. Several genes related to toxin co-regulated pilus biosynthesis proteins were also significantly enriched in June leaf samples, when compared to March and May leaf samples. Therefore, planting and harvesting times must be considered during leafy green production due to the influence of seasons in growth and proliferation of phyllosphere microbial communities.