Endophytic bacteria naturally inhabiting commercial maize seeds occupy different niches and are efficient plant growth-promoting agents

Abstract

The isolation of seed-endophytic bacteria (SEB) is a promising approach for the selection of maize plant growth-promoting bacteria (PGPB). With the hypothesis that maize seeds harbor SEB that occupy different niches and show plant-growth-promoting abilities, we aimed to isolate and characterize the potential PGPB from these seeds. The bacteria from commercial seeds (BRS Gorutuba) and axenically grown maize-seedlings were isolated, molecularly fingerprinted, and genetically characterized by amplified ribosomal DNA restriction analysis (ARDRA). All SEB were evaluated for their promotion of early root growth. The selected strains were identified by 16S rRNA sequencing and evaluated for their plant growth-promotion traits. A pot experiment was conducted to assess the ability of the SEB to promote maize-growth and nutrient accumulation. Fifty-one bacterial strains were retrieved, mostly isolated directly from the seeds. All the isolated bacteria represented different strains according to their molecular fingerprinting. ARDRA clustering revealed six clusters influenced by their plant tissue/organ of origin. Twenty-nine SEB were selected based on their influence on early root growth. The 16S rRNA sequences classified the SEB as Bacillus (22), Paenibacillus (2) and Acinetobacter (5). The inoculation of Bacillus ESA 674 improved the shoot dry mass in 57% and the Acinetobacter ESA 662 improved the root growth by 235%, both compared to the uninoculated control. At least 12 bacteria improved nutrient content in the shoots. The Bacillus spp. ESA 674 and ESA 652 outstood in improving maize nutrition by increasing the accumulation of several nutrients.