Endophytic Colonization and In Planta Nitrogen Fixation by a Herbaspirillum sp. Isolated from Wild Rice Species

Abstract

Nitrogen-fixing bacteria were isolated from the stems of wild and cultivated rice on a modified Rennie medium. Based on 16S ribosomal DNA (rDNA) sequences, the diazotrophic isolates were phylogenetically close to four genera: Herbaspirillum, Ideonella, Enterobacter, and Azospirillum. Phenotypic properties and signature sequences of 16S rDNA indicated that three isolates (B65, B501, and B512) belong to the Herbaspirillum genus. To examine whether Herbaspirillum sp. strain B501 isolated from wild rice, Oryza officinalis, endophytically colonizes rice plants, the gfp gene encoding green fluorescent protein (GFP) was introduced into the bacteria. Observations by fluorescence stereomicroscopy showed that the GFP-tagged bacteria colonized shoots and seeds of aseptically grown seedlings of the original wild rice after inoculation of the seeds. Conversely, for cultivated rice Oryza sativa, no GFP fluorescence was observed for shoots and only weak signals were observed for seeds. Observations by fluorescence and electron microscopy revealed that Herbaspirillum sp. strain B501 colonized mainly intercellular spaces in the leaves of wild rice. Colony counts of surface-sterilized rice seedlings inoculated with the GFP-tagged bacteria indicated significantly more bacterial populations inside the original wild rice than in cultivated rice varieties. Moreover, after bacterial inoculation, in planta nitrogen fixation in young seedlings of wild rice, O. officinalis, was detected by the acetylene reduction and 15 N 2 gas incorporation assays. Therefore, we conclude that Herbaspirillum sp. strain B501 is a diazotrophic endophyte compatible with wild rice, particularly O. officinalis.

Doses and application methods of Azospirillum brasilense in irrigated upland rice

“…Analyzing this agricultural scene and given the importance of this nutrient, studies that evaluate N-fixing bacteria, regarding their alternative supply of this nutrient, are an important sustainable method in agriculture (Elbeltagy et al, 2001;Guimarães et al, 2007) and can promote yield increments, which is very important because, for upland rice in the Central-West region of Brazil (3,203 kg ha -1 ), for example, is relatively lower than that of the irrigated system (6,798 kg ha -1 ) obtained in the south of the country (CONAB, 2016).…”

Metaproteogenomic analysis of microbial communities in the phyllosphere and rhizosphere of rice

“…We aimed at identifying the major physiological traits of the dominant rice-colonizing microorganisms and addressed the following research questions specifically: (1) how similar or different is the overall phyllosphere microbiota of this monocotyledonous tropically grown plant compared with the biota of the previously analyzed plant species; (2) is there evidence for microbial proteins specific for life in the phyllosphere and rhizosphere; (3) which are the potentially dominating catabolic processes of microorganisms living in association with rice, in particular in relation to onecarbon compound conversion; (4) to what extent can nitrogen fixation potential be demonstrated, considering the fact that phyllosphere bacteria and, even more so, stem endophytes have been reported to be able of nitrogen fixation, and rice is known to be colonized by diazotrophs (Elbeltagy et al, 2001;Elbeltagy and Ando, 2008;Fü rnkranz et al, 2008;Pedraza et al, 2009). Figure 1 Overview of samples analyzed in the present study and the applied methods to get insight into the identity and physiology of the rice-associated microbiota.…”

Effects of Colonization of a Bacterial Endophyte,Azospirillumsp. B510, on Disease Resistance in Rice

“…It was motile and showed pectinase and cellulase activities. 14) Although the nitrogen fixation activity of Azospirillum sp. B510 was detected in vitro, the nitrogen contribution of this strain to plant growth was very low (less than 1%) (Isawa et al, unpublished data).…”

“…12) Azospirillum, free-living nitrogen fixing rhizobacteria found in close association with plant roots and stems, is a well-studied genus of plant growth promoting bacteria (PGPB) that have beneficial effects on plants, such as increasing crop yield. 13,14) A recent study indicated that tomato plants inoculated with Azospirillum brasilense showed enhanced disease resistance against a virulent bacterial pathogen, Pseudomonas syringae pv. tomato.…”