Inoculation of Phaseolus vulgaris with the nodule-endophyte Agrobacterium sp. 10C2 affects richness and structure of rhizosphere bacterial communities and enhances nodulation and growth

Abstract

Agrobacterium sp. 10C2 is a nonpathogenic and non-symbiotic nodule-endophyte strain isolated from root nodules of Phaseolus vulgaris. The effect of this strain on nodulation, plant growth and rhizosphere bacterial communities of P. vulgaris is investigated under seminatural conditions. Inoculation with strain 10C2 induced an increase in nodule number (+54 %) and plant biomass (+16 %). Grains also showed a significant increase in phosphorus (+53 %), polyphenols (+217 %), flavonoids (+62 %) and total antioxidant capacity (+82 %). The effect of strain 10C2 on bacterial communities was monitored using terminal restriction fragment length polymorphism of PCR-amplified 16S rRNA genes. When the initial soil was inoculated with strain 10C2 and left 15 days, the Agrobacterium strain did not affect TRF richness but changed structure. When common bean was sown in these soils and cultivated during 75 days, both TRF richness and structure were affected by strain 10C2. TRF richness increased in the rhizosphere soil, while it decreased in the bulk soil (root free). The taxonomic assignation of TRFs induced by strain 10C2 in the bean rhizosphere revealed the presence of four phyla (Firmicutes, Actinobacteria, Bacteroidetes and Proteobacteria) with a relative preponderance of Firmicutes, represented mainly by Bacillus species. Some of these taxa (i.e., Bacillus licheniformis, Bacillus pumilus, Bacillus senegalensis, Bacillus subtilis, Bacillus firmus and Paenibacillus koreensis) are particularly known for their plant growth-promoting potentialities. These results suggest that the beneficial effects of strain 10C2 observed on plant growth and grain quality are explained at least in part by the indirect effect through the promotion of beneficial microorganisms.

Identification and characterization of endophytic bacteria isolated from in vitro cultures of peach and pear rootstocks

“…The taxonomy and classification of Agrobacterium are, however, questioned, and there are many disagreements regarding the nomenclature of Agrobacterium species as well as the genus. Most species have been controversially reclassified as Rhizobium species (Farrand et al 2003 ; Chihaoui et al 2015 ). Strains of Agrobacterium genus may be either tumorigenic, rhizogenic or non-pathogenic depending on the type of plasmids they comprise (Chihaoui et al 2015 ).…”

“…Most species have been controversially reclassified as Rhizobium species (Farrand et al 2003 ; Chihaoui et al 2015 ). Strains of Agrobacterium genus may be either tumorigenic, rhizogenic or non-pathogenic depending on the type of plasmids they comprise (Chihaoui et al 2015 ). Numerous reports have revealed that Agrobacterium strains recovered from the root nodules have not shown ability to re-nodulate the original hosts, thus reported as nonsymbiotic (Wang et al 2006 ; Liu et al 2010 ).…”

Mechanisms in plant growth‐promoting rhizobacteria that enhance legume–rhizobial symbioses

“…In addition, they can increase nutrient (mainly P and Fe) availability in the root zone (Chebotar et al 2001;Argaw 2012), inhibit phytopathogens (Tavares et al 2018) and modify rhizosphere chemicals, such as ethylene (Nascimento et al 2018). The use of NER can significantly increase the ability of rhizobia resident in soil to form nodules, fix N and increase growth in soybean, Glycine max (Dashti et al 1998), mung bean (Shaharoona et al 2006), chickpea, Cicer arietinum (Abdiev et al 2019) and common bean (Chihaoui et al 2015). Likewise, the use of a NER, Azospirillum brasilense, inoculated in combination with elite rhizobial strains can increase nodulation and amount of fixed N derived from symbiosis in soybean (Hungria et al 2015), common bean, Phaseolus vulgaris (Remans et al 2008) and lentil, Lens culinaris (Tsigie et al 2011).…”

Peer Review #2 of "Effects of microbial evolution dominate those of experimental host-mediated indirect selection (v0.1)"

“…probiotics) to achieve a desired host effect is now widespread, true microbiome engineering studies remain rare. Diverse examples of successful probiotic studies include: increased biomass and antioxidant capacity in plants inoculated with Agrobacterium (Chihaoui et al, 2015), reduced white pox disease in corals that received a probiotic cocktail of 13 bacterial strains isolated from coral mucus (Alagely et al, 2011), and intestinal epithelial cells with increased ability to keep pathogens from escaping the intestinal tract in mice that were administered Lactobacillus strains (Mack et al, 2003). While often successful, probiotic approaches typically rely on relatively simple manipulations of the microbiome by introducing known and culturable bacterial species.…”