Identification and use of actinomycetes for enhanced nodulation of soybean co-inoculated with Bradyrhizobium japonicum

Abstract

The utilization of actinomycetes as potential soybean (Glycine max (L.)) co-inoculants was evaluated. Soil samples from Carbondale and Belleville, Ill., were used to inoculate pre-germinated soybean plants to determine antibiotic sensitivity in the native Bradyrhizobium japonicum population. Sensitivity was in the order kanamycin > tetracycline > oxytetracycline > rifampicin > neomycin. Antagonism by five actinomycete cultures toward seven test strains of B. japonicum was also assessed. The ranking average inhibition (across all seven B. japonicum strains) by these actino mycetes was Streptomyces kanamyceticus = Streptomyces coeruleoprunus > Streptomyces rimosus > Streptomyces sp. > Amy colatopsis mediterranei. Ten antibiotic combinations were used to isolate antibiotic-resistant mutants of B. japonicum I-110 and 3I1B-110 via successive cycles of mutation. Eighty-one antibiotic-resistant strains were isolated and tested for symbiotic competency; nine of which were selected for further characterization in a greenhouse pot study. Few differences in nodule number were caused by these treatments. Nodule occupancy varied from 0% to 18.3% when antibiotic-resistant strains of B. japonicum were used as the sole inoculants. However, when three mutant strains of B. japonicum were co-inoculated with S. kanamyceticus, significant increases in nodule occupancy (up to 55%) occurred. Increases in shoot nitrogen composition (27.1%-40.9%) were also caused by co-inoculation with S. kanamyceticus.

Characterization of actinobacteria from the semiarid region, and their antagonistic effect on strains of rhizobia

“…The first record of antagonistic activity of actinobacteria against rhizobia was reported by Landerkin and Lochhead (1948), which test actinobacteria strains isolated from soil of the genus Rhizobium, and Van Schreven (1964) that compared actinobacteria of the genera Streptomyces, Actinomyces and Nocardia over Rhizobium strains. In Bradyrhizobium japonicum, Gregor et al (2003) observed inhibition of these bacteria in in vitro growth by actinobacteria of the genera Streptomyces and Amycolatopsis. Mingma et al (2014) isolated actinobacteria from roots and rhizosphere of leguminous plants which showed that, strains of the genus Streptomyces have negative effects on the growth of strains of Rhizobium sp.…”

“…The antagonistic effect of actinobacteria on the rhizobia was evaluated according to the methods of Gregor et al (2003). The strains of rhizobia were grown in glass tubes with liquid (without agar) YMA medium (10 g of mannitol, 0.5 g of K 2 HPO 4 , 0.2 g of MgSO 4 .7H 2 O, 0.1 g of NaCl, 0.5 g of yeast extract, 5 mL of bromothymol blue, 15 g of agar, 1000 mL of distilled water, and pH 6.8) (Vincent, 1970), and shaken (150 rpm) on a shaker orbital for about seven days.…”

“…The actinobacteria have crucial role in the decomposition of organic matter in ecosystems and thereby influence the cycling of nutrients in the soil (Mabrouk and Saleh, 2014), making them an excellent indicator of biological activity of the soil (Arifuzzaman et al, 2010). On the other hand, the literature contains records of the antagonistic effect of actinobacteria, in vitro and/or in vivo on other microorganisms (Parmar and Dufresne, 2011), for example, when they interact with rhizobia (Gregor et al, 2003;Mingma et al, 2014).…”

Plant growth-promoting actinobacteria: a new strategy for enhancing sustainable production and protection of grain legumes

“…Similar results were noted by other researchers as well. The combination of Streptomyces kanamyceticus and Bradyrhizobium japonicum increased nodulation and shoot N composition of soybean by up to 55 and 41%, respectively (Gregor et al 2003). Soe and Yamakawa (2013) examined the effect of co-inoculation of Bradyrhizobium yuanmingense MAS34 and Streptomyces griseoflavus P4 in enhancing nodulation, N 2 fixation, and seed yield in different soybean varieties.…”

Calcium as a Regulator of Intracellular Processes in Actinomycetes: A Review

“…That antibiotics may serve as effectors of signaling systems was clearly demonstrated in studies of the role of actinomycetes in the formation of nodules on the root hairs of leguminous plants [21,22]. Symbiotic rhizobia penetrate the cells of root hairs, causing the formation of nodules, in which nitrogen fixation takes place.…”