Effect of Xanthobacter, isolated and characterized from rice roots, on growth of wetland rice

Abstract

With an autotrophic, N-flee medium, Xanthobacter populations were isolated from the roots of wetland rice grown under field conditions. Xanthobacter populations ranged from 3.2 x 10 4 to 5.1 × 10 5 colony-forming units (cfu) g-~ of root and averaged 47-fold higher on the root or rhizoplane than in the neighbouring nonrhizosphere. Characterization studies indicated dissimilarities in carbon utilization and motility among the isolated Xanthobacter strains and other recognized Xanthobacter species. Under gnotobiotic conditions, the population of one isolate, Xanthobacter sp. JW-KR1, increased from 105 to 107 cfu plant-l 1 d after inoculation when a rice plant was present, but declined to numbers below the limit of detection (<104cfu assembly -l) after 3d in the absence of a plant. Scanning electron microscopy revealed Xanthobacter as pleomorphic forms on the rhizoplane. To assess the effect of Xanthobacter on plant growth, rice plants were grown under greenhouse conditions in plant assemblies containing sand and half-strength Hoagland's nutrient solution with and without nitrogen. Plants were either inoculated with 105 cfu Xanthobacter g-t of sand or left uninoculated. After 40 d, plants without nitrogen showed no significant differences in top or root dry weight, plant height, root length, or number of tillers or leaves, whether the plants were inoculated or uninoculated. However, when nitrogen was added, inoculated plants had a significantly larger top dry weight (15%) and number of leaves (19%) than uninoculated plants. Under conditions of added and no added nitrogen, acetylene reduction assays showed Xanthobacter sp. JW-KR1 produced <0.1 (below detection limit) and 7 nmol C2H 4 plant-~ h-1, respectively. Under the conditions studied, the results suggest that both Xanthobacter and wetland rice derive some benefits from their association.

16S Ribosomal DNA Sequence Analysis Confirms the Close Relationship between the Genera Xanthobacter, Azorhizobium, and Aquabacter and Reveals a Lack of Phylogenetic Coherence among Xanthobacter Species

“…The level of 16s rDNA sequence similarity for two strains of X. autotrophicus was 99.9%. The same high level of 16s rDNA sequence similarity was found with the X. flavus strains studied, which included marine isolate H4-14 (8) and wetland rice isolates JW/KR-1, JW/KR-2, and JW/KR-El (18,19). Both the phylogenetic tree and the 16s rDNA similarity values show that in some cases the Xanthobacter species are (7,14) by the neighbor-joining method (20).…”

Motility and chemotaxis of a Xanthobacter sp. isolated from roots of rice

“…JW-KR2 utilizes a wide range of carbon sources, including organic acids, amino acids, alcohols and some sugars (Reding et al, 1991). Growth in medium containing methanol, ethanol, 1 -propanol, 2-propanol, or butanol as the sole carbon source resulted in motile cells possessing two to five peritrichous flagella with a type I fine structure similar to X .…”

“…Xanthobacter sp. JW-KR1 multiplies in the rhizosphere of gnotobiotically grown rice and colonizes the root surface, resulting in a small benefit in plant top dry weight and number of leaves per rice plant after 41 d (Reding et al, 1991).…”

Which of soil microbes is in positive correlation to yields of maize (Zea mays L.)?

“…Some species of the family Xanthobacteraceae are able to fix dinitrogen (Reding et al 1991, Arun et (Ueki et al 2010, Kodama andWatanabe 2011). Therefore, these strains could promote development of maize because of available N and Fe source and other metabolic products (Reding et al 1991). The complex soil microbial community is crucial for plant health (Lundberg et al 2012).…”