Yeast Extract Mannitol Agar Medium Research Articles

Effect of glyphosate on the growth and survival of rhizobia isolated from root nodules of grass pea (Lathyrus sativus L.)

Grass pea (L. sativus L.) is a widely cultivated crop worldwide, forming a symbiotic relationship with nitrogen-fixing rhizobia. Glyphosate is commonly used by farmers for weed control during agricultural processes. However, the application of this chemical herbicide negatively impacts soil fertility by affecting the nitrogen-fixing rhizobia. This study aimed to assess the effects of glyphosate on rhizobia isolated from healthy and robust Grass pea plants. Specifically, Grass pea plants exhibiting vigorous growth and a healthy appearance were intentionally selected to isolate rhizobia from their root nodules. The isolated rhizobia were then characterized based on their morphological features, biochemical properties, and resistance to abiotic traits. Rhizobial isolates from grass peas exhibited Gram-negative, rod-shaped morphology, milky colony color, and variable colony sizes. Additionally, the majority displayed smooth colony surfaces on yeast extract mannitol agar medium. Based on morphological and biochemical characteristics, the isolates could be grouped under the genus Rhizobium. Optimum growth conditions for these isolates were observed at temperatures between 28 and 38 °C, pH levels ranging from 5 to 8, and salt (NaCl) concentrations of 0.5% and 1%. At a concentration of 20 mL L−1, glyphosate inhibited 5.52–47% of the Rhizobium population. The inhibition percentage increased to 17.1–53.38% at a concentration of 40 mL L−1. However, when exposed to a higher concentration (60 mL/L) of glyphosate, 87% of the isolates were inhibited. The number of colonies after glyphosate exposure was significantly dependent on concentration, and there were notable differences between treatments with varying glyphosate concentrations (p < 0.05). Glyphosate negatively impacted the survival of grass pea rhizobia, leading to a reduction in the Rhizobium population (CFU). However, the effect varied between Rhizobium isolated from grass pea root nodules.

Effect of Chemical Mutagenesis on Salt Tolerance of Common Beans (Phaseolus vulgaris L.) Nodulating Rhizobium

The chemical mutation is one of the important factors in the enrichment of the salt resistance capacity of the rhizobium isolates. Therefore, this study focused on 10 isolates of rhizobium collected from soil samples of Babile, Hararghe region, Ethiopia. All the collected isolates turned into a moderately yellow, yellow, and deep yellow color in yeast extract mannitol agar medium (YEMA) containing bromothymol blue after 48 h of incubation. It indicated that all the isolates were acid-producing Rhizobia. Moreover, based on colony morphology and diameter, 70% of the isolates displayed large mucoid colonies, and 30% of the isolates showed large watery colonies in YEMA media. Among the 10 isolates, 9(90%), 9(90%), 6(60%), 6(60%), 2(20%), and 1(10%), were grown at different salinity levels such as 2%, 4%, 6%, 8%, 9% and 10% of NaCl, correspondingly. The most salt-resistant wild isolate was HUCR 6 collected from Babile soil grown at 10% NaCl salinity level. A total of six mutants were considered after chemical mutagenesis based on their capacity to survive in the extreme salinity levels (11 to 14%). Mutant isolates such as HUCRM 4, HUCRM 5, and HUCRM 6 were the most tolerant Rhizobium that grew at the salinity level of 11 to 14% NaCl. The most sensitive mutant isolate was HUCRM 10 followed by the isolates HUCRM 8 and HUCRM 9 was the next sensitive mutant Rhizobia that grew only at 11% of NaCl concentration. Compared to the Rhizobium wild isolates, the mutant isolates were observed to be more tolerant to a medium containing higher concentration of NaCl, as high as 11% to 14%. Besides, 80% of the mutant isolates demonstrated effective nodulation with the common beans. The mutant isolate (HUCRM 4) showed better performance in relation to root nodule performance of Rhizobium species and increased the plant biomass production. In this study, mutant isolates HUCRM 6, which is tolerated to 14% NaCl, and HUCRM 4, HUCRM 5, and HUCRM 6 isolates tolerated at 12% salinity level. Finally, based on their symbiotic efficiency and tolerance to extreme salt levels, these mutant isolates (HUCRM 4, HUCRM 5 and HUCRM 6) were encouraged to be used for the development of Rhizobium inoculants of common beans grown under extreme saline conditions. J. Bio-Sci. 30(2): 13-22, 2022

Genetic characterization and diversity analysis of heavy metal-resistant rhizobacterial strains isolated from the root nodules of Vigna trilobata determined by the R.A.P.D. technique

The present study characterizes twenty-one rhizobacterial strains isolated from root nodules of Vigna trilobata cultivars collected from various Andhra Pradesh, India districts. Rhizobacteria was isolated using selective medium Yeast Extract Mannitol Agar medium (Y.E.M.A.). All 21 strains were characterized based on colony morphology and biochemical characterization and identified up to species level by 16S rDNA sequencing analysis. Different genera of the bacteria are present in the root nodules of Vigna trilobata. Short random sequence primers amplify genomic D.N.A. in a process called random amplified polymorphic D.N.A. (R.A.P.D.), which were employed to assess genetic variation across isolated bacterial strains. Banding patterns were obtained via R.A.P.D. analysis of genomic D.N.A. from the isolates using five random primers, including OPA-4, OPA-9, OPA-11, OPA-12, and OPA-15. The R.A.P.D. profiles of twenty-one rhizobacterial isolates were compared separately to determine their differences by the occurrence of polymorphic D.N.A. fragments. PCR amplified of the D.N.A. isolated from twenty-one bacterial isolates yielded seventy amplified products, of which sixty-eight were polymorphic, and two were monomorphic. The investigation found that R.A.P.D. could differentiate between the strains very precisely. Characterizing and creating novel Rhizobium species can be aided by using molecular markers to investigate genetic diversity.

Effects of Indigenous and Commercial Rhizobia on Growth and Nodulation of Soybean (Glycine max L) under Greenhouse Condition

Background: Soybean (Glycine max L.) is the most vital grain legume crop rich in protein and oil. The inoculation of rhizobia with soybean plays a very important role in increasing soil fertility via its contribution to biological nitrogen fixation. Objective: This study focuses on the evaluation of indigenous and commercial rhizobia on soybean nodulation and growth parameters. Methodology: Soil samples were collected from five districts for nodule trapping. The rhizobia were isolated using ‘plant induction following the standard procedures. The greenhouse experiments were arranged in a completed randomized design with three replications and two control units. The data were collected for plant height, nodule number, nodule dry weight, shoot dry weight, root length; root dry weight, total nitrogen and nitrogen-content. Results: The entire isolates were found gram-negative, without absorbing congo-red and did not grow on peptone glucose agar media. Slow grower isolates turned bromothymol blue with yeast extract mannitol agar medium into a moderately deep blue color but fast grower changed to yellow color. All isolates were tested on the sand induced nodule and were significantly superior to the negative control in terms of plant height, shoot dry weight, and nodule dry weight. The shoot dry weight of soybean rhizobial isolates on the sterilized sand experiment was ranging from 1.6 to 2.2g per plant and it was a highly significant correlation to the nodule number, nodule dry weight and root dry weight. Conclusion: The indigenous isolates were highly competent to all commercial rhizobia. This study encourages further evaluation of the field and molecular characteristics.

Biochemical and physiological characterizations of Rhizobium-Pea (Pisum sativum L.) symbiotic association under abiotic constraints

Pea (Pisum sativum L.) is an important leguminous for the agricultural sector. It is a source of biological nitrogen that efficiently contributes to the soil fertility. In Tunisia, low pea production is due to bad nitrogen management, lack of phosphorus availability and to the abiotic constraints. Thus, in order to improve the pea production ,a new farming technique involving the rhizobia inoculation was applied. The symbiotic, biochemical, physiological characterization and inoculation trials were performed in both the laboratory, greenhouse and open field. Pea Lincoln variety was used as legume species and fifteen Rhizobium strains isolated from the roots of the nodulated pea were collected from different Tunisian areas. Several physiological and biochemical parameters, i.e. pH, temperature, calcium carbonate and salinity were assessed to characterize the strains nodulating pea. All the rhizobia tests were evaluated on Yeast Extract Mannitol Agar medium (YEMA). Pea nodulation and Gallery API test were carried out under controlled conditions. Significant differences (p&lt;0.01) between the nodules number induced by the different bacterial strains and between strains for the dry matter quantities of aerial and root parts were registered. The pH medium test results showed that among 15 strains only 8 strains having a halo diameter greater than 1 cm at basic pH. The most of isolates are able to grow at both low and high temperatures. The limestone test results qualify these rhizobia as calcifuges. Gallery API test results showed a great diversity of rhizobia assimilation of carbohydrates implying genetic diversity. Our results us to select the most efficient solubilizer Rhizobium strains nodulating pea. In order to confirm the previously cited notions on the diversity of Rhizobium strains isolated from Pisum sativum roots in Tunisia, inoculation trial with both selected strains in controlled and open field conditions confirmed the capacity of selected strains to fix atmospheric nitrogen and promote plant growth.

Isolation and characterization of native cowpea rhizobia from Wayanad India

In the present study, eight rhizobial strains (RH-1 to RH-8) were isolated from root nodules of cowpea which grows in acidic soils of Wayanad. They were characterized based on morphological, physiological, biochemical and molecular characteristics. The results on plant growth promoting traits showed all isolates positive to IAA production, four positive to ammonia production and five positive for in vitro siderophore production. Three isolates exhibited antagonistic activity and none of them showed volatile cyanogen production. The 16S rRNA gene sequence analysis revealed all the isolates to show similarity to Rhizobium sp. While rhizobia generally have a pH range of 6.5–7.5 for optimum growth, the isolates RH-1. RH-2, RH-4 and RH-8 grew in a liquid yeast extract-mannitol agar medium at pH-4, suggesting acid tolerance in the strain of Rhizobium. The isolates were authenticated for their nodulation and growth promotion of cowpea in a paper cup experiment and four isolates (RH-2, RH-3, RH-4 and RH-5) were evaluated for their growth promotion in cowpea under field condition. It was observed that inoculation of Rhizobium increased nodulation, growth parameters and yield of cowpea compared to uninoculated control. This study showed that these rhizobial isolates with plant growth promoting traits can be used to promote the growth and yield of cow peain acidic soils of Kerala.

Biochemical and physiological characterization of Bradyrhizobium japonicum

Soybean [Glycine max (L.) Merrill] is cultivated intensively in India. Rhizobium sp. associated with it derives nitrogen (N) by biological nitrogen fixation under field conditions. Out of total 25 isolated sp. from functional root nodules of soybean plants on congo-red yeast extract mannitol agar medium, 20 slow grower Bradyrhizobium sp. and 5 fast grower Rhizobium sp. were found on growing YEMA media supplemented with bromothymol blue. The purified strains were aerobic, gram negative, non-spore forming and motile rods. The optimum growth kinetics for both sp. was 35 °C at neutral pH (7.0). Both fast and slow growing rhizobia were found to be positive for oxidase, KOH, starch hydrolysis, nitrate reduction and catalase activity. Among all the 25 isolates tested, 23 isolates showed positive reaction to gelatin hydrolysis except Bj-11 and Bj-21 while, 21 isolates were reacted positive to H2S production whereas, the four isolates viz., Bj-1, Bj-2, Bj-8 and Bj-23 were negative in reaction. While all the samples were found negative for IAA production. Pot culture experiment revealed that seed inoculation with these isolates recorded significant improvement in nodule number and plant height ranged from 3.00 to 22.00 nodules per plant and 35.00 to 65.00 cm respectively at flowering stage over uninoculated control. Isolates viz., Bj-9, Bj-10, Bj-14, Bj-17, Bj-19, Bj-23, Bj-25 could produce large and pink nodules indicating their effective symbiosis with soybean.

Rhizobial exopolysaccharides as supplement for enhancing nodulation and growth attributes of Cajanus cajan under multi-stress conditions: A study from lab to field

The present study aimed to enhance nodulation and productivity of Cajanus cajan (pigeon pea) by using rhizobia, and its metabolite, in stressed soil of Northern India where conditions of high alkalinity (pH 8.9), temperature (45 °C) and mineral N [33 ppm NO3–N (nitrate) and 48 ppm NH4–N (ammonium)] occur in combination. Farmers in the region excessively use NP fertilizers that disturbs soil ecology, and inhibits nodule formation in pigeon pea. Initial experiments were conducted in laboratory for shortlisting potent rhizobial strains. Initially survivability of different rhizobial strains was monitored under mono-stress conditions (one stress applied on bacterial strain at a time (temperature, pH or fertilizer) on yeast extract mannitol agar medium. Shortlisted strain IC3123 displayed survivability under diverse temperature and pH conditions, and fertilizer doses ranging from 30 °C to 45 °C, 4 to 12 pH and 25 % to 100 % diammonium phosphate concentrations, respectively. Dual-stress condition of pH 9 at 45 °C resulted in 1.2-fold increase in EPS production by the strain as compared to non-stressed conditions. Strain IC3123 showed much better growth profile in EPS amended medium in comparison to EPS excluded medium under multi-stress conditions, suggesting the protective role of EPS in stress tolerance. Plant growth promoting traits of IC3123 were also monitored in presence and absence of EPS supplementation that further confirmed the effectiveness of EPS in mitigating stress and enhancing plant growth promoting traits. Diverse sets of bioformulations were prepared using purified EPS alone (metabolite-based bioformulation), blend of IC3123 and EPS (blended formulation), and rhizobia cells (IC3123) alone (cell-based formulation). Field experiment was conducted with pigeon pea in naturally stressed farmer’s field in Northern India where all these stress conditions (pH 8.9, 45 °C, 33 ppm NO3–N) were found to act simultaneously in combination. The experiment was conducted in set of two: with and without 100 % recommended dose of fertilizer in the form of di-ammonium phosphate. Amongst the strategically developed bioformulations, the blend of cell plus metabolite significantly enhanced germination, pod number, seed yield, and protein content by 1.14, 1.38, 1.31 and 1.37-fold, respectively in comparison to untreated set (control). No nodulation was observed in the control set, whereas nodule number per plant increased when seeds received treatment with blend. Thus, the present study propagates the application of blended formulations developed from rhizobia and EPS for augmenting nodulation and growth of pigeon pea crop in stressed habitat in comparison to pure cell alone, with results validated in field.

Isolation and Characterization of Nodule Endophytes from Bunching and Semi-spreading Groundnut Genotypes

Bacterial endophytes prevalently colonize the internal tissues of plants and are shown to positively influence plant growth. They play a significant role in maximizing crop productivity while reducing the environmental impacts of agriculture. The aim of the present work was to isolate and characterize root nodule endophytes from two groundnut genotypes (Bunching & Semispreading). A total of 20 bacterial isolates were recovered from groundnut nodules using the yeast extract mannitol agar medium supplemented with congo red. The isolates were characterized morphologically, biochemically and compared with the reference strains Rhizobium sp. TNAU 14, Rhizobium sp. COS 1 and Bradyrhizobium sp. The isolates showed close similarity to the reference strains in their biochemical and morphological characteristics. Based on these results, it is concluded that the isolates YBB1, YBB6, YBB8, YBB14A, S27 from the bunching type and YSB 3, YSB4 and YSB5 from the semi-spreading genotype tentatively represent Rhizobium. .

Isolation of Rhizobium from root nodules of Pisum Sativum and its use as biofertilizer

Biofertilizers are substances which contain living microorganisms which when applied to a soil promote the growth by increasing the supply or availability of primary nutrients to the host plant. Biofertilizers are usually prepared as a carrier based inoculants containing effective microorganism which would show a good relationship with the host plant. This makes it easy to handle with wide range of acceptance by the host. Rhizobia are a special type of bacteria which live in root nodules in symbiotic association and fix atmospheric free nitrogen and make it available to the plants. In this study Rhizobium is isolated and cultured from the root nodules of Pisum sativum (pea plant) in a selective media i.e. YEMA (Yeast Extract Mannitol Agar medium with Congo Red). The isolate was found with poor absorption of congo red and appeared as whitish gummy colony which was biochemically tested. The isolated strain was then mixed with carrier and applied on pea. Uninoculated soil was used as control. The growth of plants was observed at regular time intervals. The growth parameters observed were germination of seed, shoot initiation, root initiation, root length and shoot length. The seed started to germinate by day 2. After 20 days the plant with the biofertilizer showed a shoot length of 11.5cm and root length of 18cm while control showed 7cm and 9cm respectively. This report showed that application of isolated rhizobial strain enhanced the growth of plant. The isolated strain can be used as biofertilizer.

Phenotyping Groundnut Rhizobia Native to Phosphorus Deficient Soils in Western Kenya

Most soils in western Kenya are characterized by high acidity level and phosphorus (P) deficiency, which affect nodulation and nitrogen fixation of groundnut (Arachis hypogaea L.). This study aimed at characterising rhizobia capable of nodulating groundnut in P deficient soils in Western Kenya. Sixty four isolates out of the 68 were confirmed to be rhizobia due to their ability to nodulate groundnut. Ninety six percent of the isolates exhibited semi-globose to globose colony shape on yeast extract mannitol agar (YEMA). Groundnut was nodulated by both fast and slow growing rhizobia isolates with 81% being fast growers. Fifty one isolates representing 75% produced acid on YEMA medium supplemented with bromothymol blue (BTB). The isolates varied in their response to pH with 39 and 61 growing at pH 4.0 and 5.5, respectively. All the isolates grew at pH 7.0 and 8.5. YEMA medium containing glucose, sucrose, starch and citrate had 64, 61, 56 and 5 isolates growing, respectively. Sixty four isolates exhibited clear zone of solubilization on medium containing dicalcium phosphate as source of inorganic phosphate. Solubilization index (SI) varied from 1.1 to 6.8. Fast-growing rhizobia isolates N01, B02, I06, Q01, F05, C02, E01, Q03, I01 and B01 recorded the highest solubilization index of 3.8, 4.5, 4.6, 4.6, 4.7, 5.0, 5.1, 6.1, 6.1 and 6.8, respectively. Groundnut rhizobia showed variation in their potential to solubilize inorganic phosphate and effectively nodulate the host. The most promising isolates from this study would be used as bio-fertilizer upon further validation in the greenhouse and field.

Isolation and Screening of Indigenous Bambara Groundnut (Vigna Subterranea) Nodulating Bacteria for their Tolerance to Some Environmental Stresses

Environmental stresses are important limiting factors for crops production. The aim of this experiment is to isolate Legume Nodulating Bacteria (LNB) obtained from root nodules of bambara groundnut (Vigna subterranea L.) plants and evaluate their performance under some environmental constraints. Samples were collected in Cameroon from three location sites of the Humid-forest zone: Logbessou in the Littoral region; Mfoua in the South and Boga in the Centre region. Nodulation of bambara groundnut was examined in plastic bags and root nodules were collected from seedling. After their isolation, the bacteria were confirmed as LNB by re-nodulating Macroptilium atropurpureum. The morphological, cultural and phenotypic characteristics (utilization of carbon, tolerance to salt, pH, aluminium) of isolates were determined. The results obtained were analyzed statistically by ANOVA using the software SPSS analysis version 11.5. Duncan test was used to measure the difference among the means at a level of p<0.05. A collection of 18 isolates was obtained on Yeast Extract Mannitol Agar medium. Authentication experiments, confirmed that the majority of the isolates (66.67%) were LNB due to their ability to infect the host plant. Bambara groundnut isolates are different morphologically. Dendrogram of the phenotypic characteristics showed that, below the boundary level of 50% average similarity, isolates fell into at least three distinct groups. All isolates showed fast-growing capacity. Most isolates (66.67%) were able to grow in a medium with pH as low as and Al concentration of 50 µM (58.33 %). Some isolates (50%) showed weak growth capacity at 4% NaCl. The bambara groundnut isolates tested were able to use a broad range of carbohydrates as sole source of carbon. The isolates from the present study may be useful to increase the symbiotic nitrogen fixation in legume.

English

Salinity stress severely affects growth, nodulation and yield of chickpea (Cicer arietinum L.). However, inoculation with Mesorhizobium strains containing 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase improves the plant growth by reducing the level of ethylene induced by salt stress. Fifty (50) Mesorhizobium isolates were obtained from nodules of chickpea plants on yeast extract mannitol agar (YEMA) medium. Mesorhizobium isolates were screened for ACC utilization and growth at different salt concentrations in YEMA medium. Six salt tolerant Mesorhizobium isolates were checked for their role in plant growth promotion under pot house conditions in chillum jar assembly. Mesorhizobium strains having ACC utilization ability caused an increase in the nodule number, nodule weight and shoot dry weight after plant growth for 50 and 80 days, both with and without NaCl. Mesorhizobium isolate MBD26 showed 294 mg/plant shoot dry weight without salt condition after 50 days of plant growth. Mesorhizobium isolate MBD26 increased shoot dry weight by 49.52% (without salt) and 41.53% in the presence of salt (40 mM NaCl) after 80 days of plant growth. It was observed that inoculation with Mesorhizobium isolates containing ACC-deaminase improved nodulation and plant growth of chickpea over ACC deaminase lacking isolates. Thus, inoculation with Mesorhizobium strains possessing ACC utilization ability could be a sustainable approach to improve plant growth under salinity stress. Key words: 1-Aminocyclopropane-1-carboxylic acid (ACC) utilization, salt stress, Mesorhizobium, chickpea, nodulation, plant growth.

English

Carrot hairy root induction by two different strains of Agrobacterium rhizogenes- MTCC- 532 and MTCC- 2364 grown in yeast extract mannitol agar medium (YEMA) was studied in carrot (Daucus carota). The maximum hairy root induction was observed when carrot was simmered with 48 h old culture of A. rhizogenes MTCC-532. With different concentrations of acetosyringone (AS) tested, addition of 150 &micro;M acetosyringone was found to enhance the transformation frequency up to 75(&plusmn;2.60)a and 60 (&plusmn;2.08)a percentage by A. rhizogenes MTCC-532 and MTCC 2364 strains, respectively. Transformation efficiency was highly dependent on the acetosyringone concentrations, type of bacterial strains and carrot genotype. Transfer of Ri Ti-DNA was confirmed by polymerase chain reaction (PCR) analysis, the detection of ags gene in transformed carrot hairy root. A. rhizogenes transformed hairy roots had the ability to form copious lateral roots as well as a negative geotropic growth habit in a shorter period of time. The Murashige and Skoog (MS) medium was found to be the best medium for hairy root mass multiplication, which induced high root biomass production and rapid root tip elongation.&nbsp; Key words: Carrot, Agrobacterium rhizogenes, acetosyringone, hairy roots, Murashige and Skoog (MS) medium, arbuscular mycorrhizae.

The Effect of pH Stress on the Survival of Rhizobium Trifolii and Sinorhizobium Meliloti in Vitro

Nitrogen-fixing symbiotic bacteria known as rhizobia can exist in different soils and adapt to different environmental conditions. The aim of this study was to determine the impact of pH on the growth of Rhizobium trifolii and Sinorhizobium meliloti. Rhizobial species were isolated using yeast extract mannitol agar medium) in which the pH values were adjusted to 5.0, 6.0, 8.0 and 9.0 by adding HCl and NaOH. The optimum pH for rhizobia is neutral or slightly alkaline (pH 8) and they are more sensitive to acidity. Sinorhizobium meliloti developed better in an acid medium compared to Rhizobium trifolii.

Isolation and characterization of salt-tolerant rhizobia native to the desert&lt;br&gt;soils of United Arab Emirates

The salinity tolerance of naturally occurring rhizobia, isolated from the root nodules of three leguminous plants, namely sesbania (Sesbania sesban), lablab (Lablab purpureus) and pigeonpea (Cajanus cajan), growing at a research farm in Dubai (United Arab Emirates) was studied. Eight isolates identified from colony morphology and gram staining reaction, when cultured on yeast extract-mannitol agar medium (YEMA) supplemented with different concentration of sodium chloride (NaCl), produced colonies even at salinities as high as 40 dS m-1. The rhizobial isolates were also found to be effective in nodulating 21-day old seedlings grown in potting soil and irrigated with saline water of up to 12 dS m-1 after inoculation. The tolerance to high levels of salinity and the survival and persistence in severe and harsh desert conditions make these rhizobia highly valuable inoculums to improve productivity of the leguminous plants cultivated under extreme environments.

Effect of Rhizobium on Growth and Biomass Production of Rice

To characterize twenty Rhizobium strains isolated from nodules of lentil, grasspea and chickpea, an experiment was conducted in the Soil Microbiology laboratory of the Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, Bangladesh. The isolates were tested for growth on Congo red Yeast Extract Mannitol (YEM) agar, peptone glucose agar, and YEM agar containing Bromothymol blue (BTB). All the strains except Ls 12 absorbed Congo red dye very weekly. Except Le 2 strains, isolated from lentil showed no growth in peptone glucose agar. All the strains isolated from grasspea and chickpea showed moderate growth on this medium. All the strains were fast-growing and showed acidic reaction on YEM agar medium. Among the strains isolated from lentil, Le 1, Le 2 and Le 4 produced moderate turbidity while Le 3, Le 6, Le 7 and Le 8 produced high turbidity in YEM broth. All the strains isolated from grasspea except Ls 3 and chickpea except Ca 1 produced moderate turbidity in YEM broth medium. Strains Ls 3 and Ca 1 produced high turbidity. To assess the effect of ten of these Rhizobium isolates viz. Le 1, Le 4, Le 6, Le 8, Ls 1, Ls 2, Ls 6, Ls 7, Ca 3 and Ca 4 on growth and biomass production of rice, a follow-up experiment was conducted in the same laboratory. Root length of rice was significantly increased over control (without inoculation) due to inoculation with different Rhizobium strains. The highest root length (9.63 cm) was obtained by inoculation with strain Ls 6 isolated from lentil. All the Rhizobium strains produced significantly higher shoot length, fresh and dry biomass over control. The highest shoot length (16.50 cm), fresh biomass (138.3 mg) and dry biomass (27.75 mg) were also obtained from the strain Ls 6. DOI: http://dx.doi.org/10.3329/bjm.v28i2.11818 Bangladesh J Microbiol, Volume 28, Number 2, December 2011, pp 64-68

Population of Rhizobium bacteria in the soil at several plant from Buton island, Muna regency, Southeast Sulawesi

The research was conducted in order to know population of Rhizobium bacteria in the soil at several plant from Buton island, Muna regency, Southeast Sulawesi. The purpose of the study was to get the population data and pure cultures of Rhizobium bacteria.Rhizobium bacteria were isolated from 13 sample from rhizosphere of fruit plant, 14 sample soil from rhizosphere of yield plant, 5 sample soil from rhizosphere of horticulture plant, and 8 sample soil from forest plant. Isolation was done in standard medium Yeast Extract Mannitol Agar (YEMA), the inculation at (27-280C), and the population with plate count methods. The growth characteristic of strain was observed by using YEMA medium mixed respectively with Brom Thymol Blue and Congo Red as indicators.The population of Rhizobium bacteria was in the range of 7-115 X 105 CFU/g soil, and the highest population was found from the sample soil from rhizosphere with Ipomea batatas plant. Fourty nine gave of pure culture, thirty five isolates can be grouped as fast growing, while fourteen can be grouped as slow growing.

Impact of zinc-tolerant plant growth-promoting rhizobacteria on lentil grown in zinc-amended soil

Though zinc is a plant nutrient at low levels, Zn ions can be highly phytotoxic at higher concentrations found in contaminated soils. Plant growth-promoting rhizobacteria can be used to decrease this toxicity. Indeed, in addition to their role in plant-growth promotion, rhizobacteria also reduce the toxicity of heavy metals. In turn, they can be effective for crops grown in metal-contaminated soils. Here, we isolated a zinc-tolerant plant growth-promoting rhizobacterium, Rhizobium species RL9, from a zinc-contaminated soil and assayed its plant growth-promoting activities in vitro. We found that the rhizobacterium strain RL9 tolerated zinc up to a concentration of 400 μg mL−1 on yeast extract mannitol agar medium. It produced 33 μg mL−1 of indole acetic acid in Luria Bertani broth at 100 μg mL−1 of tryptophan and was positive for siderophore, hydrogen cyanide and ammonia. Such phytohormones released by this strain could help in promoting the growth of legumes. We further tested the effect of rhizobacterium strain RL9 on lentils grown in zinc-amended soil. We found that when the rhizobacterium strain RL9 was added to soil contaminated with Zn at 4890 mg/kg, lentil dry matter increased by 150%, nodule numbers by 15%, nodule dry mass by 27%, leghaemogloblin by 30%, seed yield by 10% and grain protein by 8%, compared with uninoculated plants. We also found that the concentration of zinc was higher in uninoculated plant organs than in the inoculated counterpart. Our findings thus suggest that rhizobacterium strain RL9 could be exploited for bacteria-assisted reduction of zinc toxicity in zinc-contaminated soils due to its intrinsic abilities of expressing growth-promoting substances and reduction of the toxic effects of zinc.

Effect of metal tolerant plant growth promoting Bradyrhizobium sp. ( vigna) on growth, symbiosis, seed yield and metal uptake by greengram plants

The nickel and zinc tolerant plant growth promoting Bradyrhizobium sp. ( vigna) RM8 was isolated from nodules of greengram, grown in metal contaminated Indian soils. The plant growth promoting (PGP) potentials of strain RM8 was assessed both in the presence and absence of nickel and zinc under in vitro conditions. Strain RM8 tolerated a high level of nickel (300 μg ml −1) and zinc (1400 μg ml −1) on yeast extract mannitol agar medium. Bradyrhizobium sp. ( vigna) strain RM8 produced 13.3 μg ml −1 of indole acetic acid in Luria Bertani broth at 100 μg ml −1 of tryptophan which increased to 13.6 μg ml −1 at 50 μg Ni ml −1 and 13.5 μg ml −1 at 300 μg Zn ml −1. Strain RM8 was positive for siderophore, HCN and ammonia both in the absence and presence of nickel and zinc. The PGP activity of this strain was further evaluated with increasing concentrations of nickel and zinc using greengram as a test crop. The bio-inoculant enhanced the nodule numbers by 82%, leghaemoglobin by 120%, seed yield by 34%, grain protein by 13%, root N by 41% and shoot N by 37% at 290 mg Ni kg −1 soil. At 4890 mg Zn kg −1 soil, the bioinoculant increased the nodule numbers by 50%, leghaemoglobin by 100%, seed yield by 36%, grain protein by 13%, root N by 47% and shoot N by 42%. The bioinoculant strain RM8 reduced the uptake of nickel and zinc by plant organs compared to plants grown in the absence of bioinoculant. This study suggested that the bioinoculant due to its intrinsic abilities of growth promotion and attenuation of the toxic effects of nickel and zinc could be exploited for remediation of metal from nickel and zinc contaminated sites.