Identification of effective Rhizobium isolate(s) for efficient symbiosis with soybean under moisture stress conditions

The objective of the paper is to observe the effectiveness of Bradyrhizobial species on symbiosis with soybean under moisture stress conditions. In physiological tests, treatment T3: B. daqingense (under irrigated condition) showed significant amount of leghaemoglobin content (1.82 mg). Proline content was recorded highest (2.8 mg g-1 seed) in T8 B. liaoningense in stress. Highest chlorophyll content (1.84 mg/LFW) was recorded in T4 B. liaoningense under irrigated condition. The highest N-uptake in plant shoot, root and grain was obtained in B. daqingense under irrigated condition. Similarly, highest was obtained in in treatment T3 B. daqingense under irrigated condition. At R8 stage, grain yield was significantly highest (6.48 g) in treatment T3 (B. daqingense under irrigated condition). In both irrigated and moisture stress conditions bradyrhizobial strains B. daqingense (treatment T3 and Treatment T7) were most effective in terms of nitrogen fixation, nitrogen accumulation, phosphorus accumulation, shoot dry weight, root dry weight and grain yield as compared to the other treatments.

A Sulfoglycolytic Entner-Doudoroff Pathway in Rhizobium leguminosarum bv. trifolii SRDI565

ABSTRACT Rhizobia are nitrogen-fixing bacteria that engage in symbiotic relationships with plant hosts but can also persist as free-living bacteria in the soil and rhizosphere. Here, we show that free-living Rhizobium leguminosarum SRDI565 can grow on the sulfosugar sulfoquinovose (SQ) or the related glycoside SQ-glycerol using a sulfoglycolytic Entner-Doudoroff (sulfo-ED) pathway, resulting in production of sulfolactate (SL) as the major metabolic end product. Comparative proteomics supports the involvement of a sulfo-ED operon encoding an ABC transporter, sulfo-ED enzymes, and an SL exporter. Consistent with an oligotrophic lifestyle, proteomics data revealed little change in expression of the sulfo-ED proteins during growth on SQ versus mannitol, a result confirmed through biochemical assay of sulfoquinovosidase activity in cell lysates. Metabolomics analysis showed that growth on SQ involves gluconeogenesis to satisfy metabolic requirements for glucose-6-phosphate and fructose-6-phosphate. Metabolomics analysis also revealed the unexpected production of small amounts of sulfofructose and 2,3-dihydroxypropanesulfonate, which are proposed to arise from promiscuous activities of the glycolytic enzyme phosphoglucose isomerase and a nonspecific aldehyde reductase, respectively. The discovery of a rhizobium isolate with the ability to degrade SQ builds our knowledge of how these important symbiotic bacteria persist within soil. IMPORTANCE Sulfonate sulfur is a major form of organic sulfur in soils but requires biomineralization before it can be utilized by plants. Very little is known about the biochemical processes used to mobilize sulfonate sulfur. We show that a rhizobial isolate from soil, Rhizobium leguminosarum SRDI565, possesses the ability to degrade the abundant phototroph-derived carbohydrate sulfonate SQ through a sulfoglycolytic Entner-Doudoroff pathway. Proteomics and metabolomics demonstrated the utilization of this pathway during growth on SQ and provided evidence for gluconeogenesis. Unexpectedly, off-cycle sulfoglycolytic species were also detected, pointing to the complexity of metabolic processes within cells under conditions of sulfoglycolysis. Thus, rhizobial metabolism of the abundant sulfosugar SQ may contribute to persistence of the bacteria in the soil and to mobilization of sulfur in the pedosphere.

Molecular diversity of rhizobial isolates of horse gram [MACROTYLOMA UNIFLORUM [Lam] Verdc.] and it's biochemical characterization under in-vitro conditions

The present research was conducted to isolate and characterize native rhizobium isolates from the root nodules of horse gram [MACROTYLOMA UNIFLORUM [Lam] Verdc.] plants grown under sub-humid to semi-arid regions of Rajasthan in India. These plants were collected from various locations of Rajasthan viz; Banswara, Bhilwara, Pratapgarh and Udaipur districts in India under variable agro-climatic regions. Total nine rhizobial isolates were characterized based on morphological and biochemical analysis. Majority of the isolates showed pH, NaCl concentration and temperature tolerance between 6.0to 8.0, 0.5 to 3.0 per cent and 34 to 40 0C respectively. The horse gram rhizobium isolate R5 showed tolerant towards temperature and NaCl concentration upto 450C and 5% respectively whereas the isolate R3 showed positive growth upto alkaline pH of 10.0. The molecular characterization based on RAPD revealed that rhizobium isolates are closely related to each other as only two major clusters was formed based on Jaccards, s similarity coefficient.

Uji Asosiasi Bakteri Rhizobium Terseleksi dengan Leguminosa Pakan dalam Kondisi Tercekam Salin

(Test of Association Selected Rhizobium Bacteria with Legumes in Salinity Stress) ABSTRACT. The research aim was to investigate association selected rhizobium bacteria with legumes in salinity stress. Plant media was salin soil that have EC = 20.45 mmhos/cm which taken from Morosari beach, Sayung, Demak. Rhizobium isolate applied was tolerant to 12.000 ppm of NaCl that equaled to electrical conductivity of 20 mmhos/cm. The research was carried out in green house of Laboratory of Forage Science Diponegoro University Semarang. The design arranged was completely randomized design with factorial design 2 x 4 in 3 repeatations. First factor was kind of legumes, T1 = lamtoro (Leucaena leucocephala); T2 = turi (Sesbania grandiflora). and second factor was kind of rhizobium isolates, I1 = without isolate; I2 = rhizobium that was isolated from lamtoro, I3 = rhizobium that was isolated from turi; I4 = combination isolate from lamtoro and turi. The crop growth was observed up to 10 weeks of age. The parameters were 1) crops heigh; 2) sum of leaf crops; 3) fresh weight production; 4) dry weight production; 5) amount and fresh weigh of effective root nodules. The study showed the growth and production of turi in saline media of EC 20.45 mmhos/cm was higher than lamtoro. Root nodule of turi was formed, but lamtoro was not. Turi was more tolerant than lamtoro at very saline media.

Renodulation and nitrogen fixing potential of Acacia nilotica inoculated with Rhizobium isolates

Renodulation and nitrogen fixation potential of indigenous and exotic isolates of Rhizobium were studied in a field experiment with Acacia nilotica from July 1990 to June 1991. The inoculum isolates belonged to different serotypes and did not show cross-reaction with the native population of Rhizobium. Nitrogenase activity of root nodules observed at 4-month intervals covering three seasons snowed a decline during winter months, which corresponded with the senescence of the nodules. Maximal renodulation as checked by serotyping and antibiotic resistance pattern was observed with isolate AB 3 followed by AD 4 and USDA 3325. The highest nitrogenase activity was exhibited in plants inoculated with AD 4 at 12 months. Plants inoculated with Rhizobium isolate USDA 3325 showed the highest increase in dry-matter yield at 12 months. Except for AB 3, dual inoculation with Rhizobium isolates and Glomus fasciculatum did not enhance dry matter production as compared with uninoculated controls or single inoculation of either Rhizobium isolate or G. fasciculatum.Key words: Rhizobium, Acacia nilotica, nitrogenase activity, renodulation.