Abstract
BackgroundPlant-bacteria associations have been extensively studied for their potential in increasing crop productivity in a sustainable manner. Serratia marcescens is a species of Enterobacteriaceae found in a wide range of environments, including soil.ResultsHere we describe the genome sequencing and assessment of plant growth-promoting abilities of S. marcescens UENF-22GI, a strain isolated from mature cattle manure vermicompost. In vitro, S. marcescens UENF-22GI is able to solubilize P and Zn, to produce indole compounds (likely IAA), to colonize hyphae and counter the growth of two phytopathogenic fungi. Inoculation of maize with this strain remarkably increased seedling growth and biomass under greenhouse conditions. The S. marcescens UENF-22GI genome has 5 Mb, assembled in 17 scaffolds comprising 4662 genes (4528 are protein-coding). No plasmids were identified. S. marcescens UENF-22GI is phylogenetically placed within a clade comprised almost exclusively of non-clinical strains. We identified genes and operons that are likely responsible for the interesting plant-growth promoting features that were experimentally described. The S. marcescens UENF-22GI genome harbors a horizontally-transferred genomic island involved in antibiotic production, antibiotic resistance, and anti-phage defense via a novel ADP-ribosyltransferase-like protein and possible modification of DNA by a deazapurine base, which likely contributes to its competitiveness against other bacteria.ConclusionsCollectively, our results suggest that S. marcescens UENF-22GI is a strong candidate to be used in the enrichment of substrates for plant growth promotion or as part of bioinoculants for agriculture.
Highlights
Plant-bacteria associations have been extensively studied for their potential in increasing crop productivity in a sustainable manner
Identification of the isolate During the initial characterization of abundant culturable bacteria from mature cattle vermicompost, we identified a notorious pigmented bacterium that was preliminarily characterized as S. marcescens by colony morphology, microscopy and 16S rRNA sequencing
Our results clearly show that S. marcescens Universidade Estadual do Norte Fluminense Darcy Ribeiro (UENF)-22GI solubilizes P and Zn in vitro, with solubilization index (SI) values of 2.47 ± 0.22 and 2.11 ± 0.47, respectively (Fig. 1a and b)
Summary
Plant-bacteria associations have been extensively studied for their potential in increasing crop productivity in a sustainable manner. PGPR can promote plant growth by various mechanisms, such as: 1) mitigation of abiotic stresses such as metal phytotoxicity [9], water or salinity stress [10]; 2) activation of defense mechanisms against phytopathogens [11]; 3) directly attacking pathogens [12]; 4) biological nitrogen fixation [13]; 5) solubilization of mineral nutrients (e.g. P and zinc, Zn) [14]; 6) production phytohormones [15] and; 7) secretion of specific enzymes (e.g., 1-aminocyclopropane-1-carboxylate deaminase) [16] Due to their beneficial effects, there is a growing market for PGPR biofertilizers [17], which are based on bacteria of various genera, such as Azospirillum, Bacillus, and Azotobacter [18]. A notable example of successful application of PGPR in agriculture is the soybean (Glycine max L.) production in Brazil, in which the development and use of an optimized consortium of different strains of Bradyrhizobium sp. [19] led to very high productivity levels at significantly lower costs due to the virtually complete replacement of nitrogen fertilizers [20]
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