Metatranscriptomics and nitrogen fixation from the rhizoplane of maize plantlets inoculated with a group of PGPRs

Abstract

24The free-living soil bacteria that are beneficial for the growth of plants are known as 25 plant growth-promoting rhizobacteria (PGPR). In this work, a multi-species of PGPR 26 bacteria inoculant was designed, which included nitrogen-fixing strains such as 27 Rhizobium phaseoli, Sinorhizobium americanum and Azospirillum brasilense, as well as 28 other plant growth promoting bacteria such as Bacillus subtillis and Methylobacterium 29 extorquens. The multi-species community exerted a beneficial effect on plant seedlings 30 when it was inoculated, greater than the effect observed when inoculating each bacteria 31 individually. Acetylene reduction of maize roots was recorded with the multi-species 32 inoculant, which suggests that nitrogen fixation occurred under these conditions. To 33 analyze the contributions of the different nitrogen-fixing bacteria that were inoculated, a 34 metatranscriptomic analysis was performed. The differential expression analysis 35 revealed that the predominantly nif transcripts of Azospirillum are overexpressed, 36 suggesting that it was responsible for nitrogen fixation in maize. Overall, we analyzed 37 the interaction of a synthetic community, suggesting it as an option, for future 38 formulations of biofertilizers. 39 IMPORTANCE 40While nodulation processes and nitrogen fixation by rhizobia have been well studied, 41 little is known about the interaction between rhizobia and non-leguminous plants such 42 as maize, which is used as a model for this study. Nitrogen fixation in cereals is a long 43 searched goal. Instead of single species inoculants, multi-species inoculation may be 44 more efficient to promote plant growth and fix nitrogen. Metatrascriptomes allowed us 45 to recognize the bacteria responsible for nitrogen fixation in plant rootlets. The study of 46 the function of certain genes may help to understand how microorganisms interact with 47 3 the root plant, as well as allow a better use of microorganisms for the generation of 48 novel biofertilizers using microbial consortia. 49 INTRODUCTION 50 In nature and in agricultural fields there is a large diversity of bacteria associated with 51 plants. Once isolated in culture media and subsequently tested individually in plant 52 assays, many plant-bacteria prove to be capable of promoting plant growth. Bacterial 53 mechanisms of action are diverse, and some bacteria may exhibit more than one 54 mechanism. Plant growth promoting rhizobacteria (PGPR) may produce phytohormones 55 or volatiles, solubilize nutrients, fix nitrogen or inhibit pests/pathogens. Among them, 56 nitrogen-fixing bacteria are in general a minority, possibly due to the metabolic charge 57 of fixing nitrogen. 58 As bacteria are not alone in soil and in plants, recent inoculation assays have considered 59 the use of more than single strains, and combinations of Azospirillum and rhizobia or 60 Bacillus and rhizobia have been more successful than single-strain inoculants in 61 promoting plant growth (reviewd in 1-3). For example, Azospirillum and 62 Br...

Salinity stress endurance of the plants with the aid of bacterial genes

“…The gene expression of Azospirillum lipoferum 4B during interaction with rice roots was assayed ( Drogue et al, 2014 ). A metatranscriptomic study was conducted to investigate the contributions of different nitrogen-fixing bacteria present in the maize inoculated liquid ( Gomez-Godinez et al, 2018 ). Metabolomics was applied to explore the exo-metabolome of three PGPB ( Pseudomonas putida IDE-01, Azospirillum brasilense IDE-06, and Bacilus megaterium IDE-14) in interaction with maize and rice ( Garcia et al, 2022 ).…”

Pathogen Biocontrol Using Plant Growth-Promoting Bacteria (PGPR): Role of Bacterial Diversity

“…Recently, using metatranscriptomic analysis, Gómez-Godínez et al (2019) revealed that Azospirillum nif genes were upregulated in the presence of other PGPR species, resulting in active nitrogen fixation by A. brasilense in maize roots [ 15 ]. Similarly, it was shown that the individual bacterial agents within PGPR communities differentially express their disease-suppressive traits [ 14 , 16 ], and accordingly induce the tuning of genes and metabolic pathways in host plants to achieve specific targets that benefit agriculture.…”

“…Multiple mechanisms of action have been postulated as to how this defense arises, including direct competition for nutrients and niches, antibiosis, enzyme lysis, signal interference and indirect induction of host resistance [ 7 , 8 , 10 , 11 , 12 ]. The accumulated evidence suggests PGPR taxa vary in the expression of traits [ 13 , 14 , 15 ] that correlate with one or more of the above mechanisms, thereby altering their capacities for protecting host plant from pathogens and thus promoting plant growth. Since PGPR live in communities on the root surface or sometimes inside the root (i.e., endophytes) and they are recruited by host plants, it has been deemed that each bacterial ‘component’ offers specific benefits for plants [ 16 ].…”

The Contrivance of Plant Growth Promoting Microbes to Mitigate Climate Change Impact in Agriculture

“…Some of the PGPB act synergistically when applied together or coexist, such as B. subtilis with mycorrhizal fungi [ 9 , 19 ]. Gomez-Godinez et al revealed a stronger effect on maize when using multispecies inoculum of PGPB than single bacteria [ 131 ]. Inoculation with a single microbial culture may place the isolates in a worst position, because may suffer from competitive and deleterious effects of local soil microorganisms [ 108 , 132 ].…”