Colonization of lettuce rhizosphere and roots by tagged Streptomyces

Abstract

Beneficial microorganisms are increasingly used in agriculture, but their efficacy often fails due to limited knowledge of their interactions with plants and other microorganisms present in rhizosphere. We studied spatio-temporal colonization dynamics of lettuce roots and rhizosphere by genetically modified Streptomyces spp. Five Streptomyces strains, strongly inhibiting in vitro the major soil-borne pathogen of horticultural crops, Sclerotinia sclerotiorum, were transformed with pIJ8641 plasmid harboring an enhanced green fluorescent protein marker and resistance to apramycin. The fitness of transformants was compared to the wild-type strains and all of them grew and sporulated at similar rates and retained the production of enzymes and selected secondary metabolites as well as in vitro inhibition of S. sclerotiorum. The tagged ZEA17I strain was selected to study the dynamics of lettuce roots and rhizosphere colonization in non-sterile growth substrate. The transformed strain was able to colonize soil, developing roots, and rhizosphere. When the strain was inoculated directly on the growth substrate, significantly more t-ZEA17I was re-isolated both from the rhizosphere and the roots when compared to the amount obtained after seed coating. The re-isolation from the rhizosphere and the inner tissues of surface-sterilized lettuce roots demonstrated that t-ZEA17I is both rhizospheric and endophytic.

Plant growth promotion by streptomycetes: ecophysiology, mechanisms and applications

“…Lastly, research to develop methods of bioinoculant delivery and timing must be carried out in the greenhouse and field to maximize the plant response to the applied bioinoculant. It has been found that applying streptomycetes is different to applying Gram-negative bacteria because better plant responses have generally been obtained when the streptomycete application to the soil or substrate occurred before sowing the seeds, thus allowing the selected strain to colonize and establish [6,137,138].…”

“…Since the endophytic compartment represent a more protective niche for plantbacteria interaction, formulations based on endophytic streptomycete strains had advantages over non-endophytic streptomycetes that would guarantee successful positive plant host response [139]. Representative streptomycetes possess the ability to colonize the rhizosphere or endophytic tissues of plants [6,87], to produce spores resistant to irradiation, heat, and drought [12], and to have an impressive range of metabolites with a variety of biological activities [140]. Streptomyces may also convert plant exudates or macromolecules/supramolecules present in the rhizosphere into a form that can be used by other plant growth-promoting microbes.…”

“…Besides the well-studied Gramnegative plant-associated bacteria, Gram-positive bacteria can also have beneficial interactions with plants and promote plant growth [6][7][8]. Streptomyces is the most widely studied genus of Gram-positive PGPB and is the central subject of this review.…”

Evaluation of biocontrol properties of Streptomyces spp. isolates against phytopathogenic fungi Colletotrichum gloeosporioides and Microcyclus ulei

“…In agriculture, numerous Streptomyces species have demonstrated capability of controlling diverse fungal phytopathogens of great agroindustrial impact (Samac and Kinkel, 2001;Taechowisan et al, 2003;Tian et al, 2004;Khamna et al, 2009;Zarandi et al, 2009;Gopalakrishnan et al, 2011;Li et al, 2012;Kanini et al, 2013). However, relatively few biological inoculants have been developed for crop use, mainly based on the poor association between the efficiency determined in the laboratory compared to the one observed in the greenhouse or the field (Bonaldi et al, 2015).…”

Effective Colonization of Spinach Root Surface by Rhizobium

“…Several markers were developed to study localization and quantification of PGPR: (i) antibiotic resistance (Gamalero et al 2003;Bonaldi et al 2015) and (ii) fluorescent markers for colonization studies (Cao et al 2011;Krzyzanowska et al 2012). These studies focus on a basic knowledge between PGPR and the host plant in axenic conditions.…”