Growth Promotion of Giant Duckweed Spirodela polyrhiza (Lemnaceae) by Ensifer sp. SP4 Through Enhancement of Nitrogen Metabolism and Photosynthesis

Duckweeds (Lemnaceae) are representative producers in fresh aquatic ecosystems and also yield sustainable biomass for animal feeds, human foods, and biofuels, and contribute toward effective wastewater treatment; thus, enhancing duckweed productivity is a critical challenge. Plant-growth-promoting bacteria (PGPB) can improve the productivity of terrestrial plants; however, duckweed-PGPB interactions remain unclear and no previous study has investigated the molecular mechanisms underlying duckweed-PGPB interaction. Herein, a PGPB, sp. strain SP4, was newly isolated from giant duckweed ( ), and the interactions between and SP4 were investigated through physiological, biochemical, and metabolomic analyses. In and SP4 coculture, SP4 increased the nitrogen (N), chlorophyll, and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) contents and the photosynthesis rate of by 2.5-, 2.5-, 2.7-, and 2.4-fold, respectively. Elevated photosynthesis increased the relative growth rate and biomass productivity of by 1.5- and 2.7-fold, respectively. Strain SP4 significantly altered the metabolomic profile of , especially its amino acid profile. N stable isotope analysis revealed that organic N compounds were transferred from SP4 to . These N compounds, particularly glutamic acid, possibly triggered the increase in photosynthetic and growth activities. Accordingly, we propose a new model for the molecular mechanism underlying growth promotion by its associated bacteria sp. SP4, which occurs through enhanced N compound metabolism and photosynthesis. Our findings show that sp. SP4 is a promising PGPB for increasing biomass yield, wastewater purification activity, and CO capture of .[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.