High and low nodulation in relation to molecular diversity of chickpea mesorhizobia in Indian soils

Chickpea (Cicer arietinum L.) nodulation variants of two cultivars ICC 4948 and ICC 5003 were used as trap plants to isolate 385 native rhizobia from CCS Haryana Agricultural University, Hisar farm soil. After authentication and considering growth characteristics, selected 110 rhizobia revealed immense molecular diversity using the profiles of DNA fragments generated by Polymerase chain reaction (PCR) with enterobacterial repetitive intergeneric consensus (ERIC) sequences. Low nodulating variants of cvs ICC 4948 and ICC 5003 were able to trap more numbers of rhizobial genotypes, namely seven as compared four to five by high nodulating variants of these cultivars. Overall eight rhizobial genotypes were trapped by the chickpea cultivars. Rhizobial isolates from same nodule or same plants were present in the same or different clusters and few isolates showed 100% similarity also. Based on nodules from a plant, nodulation variant or cultivar, rhizobia could not be differentiated and no exclusive cluster was formed by either rhizobial isolates from low or high nodulating variants of both the cultivars. Two most efficient rhizobial isolates LN 707b and LN 7007 were characterized by amplification and sequencing of 16S rRNA gene. Rhizobial isolate LN 707b showed more than 98% similarity with Mesorhizobium sp SH 2851 and Mesorhizobium mediterraneum. Another isolate LN 7007 showed more than 99% similarity with the sequence of 16S r RNA gene of Mesorhizobium sp STM 398, and M. mediterraneum. So the chickpea rhizobia from Northern Indian subcontinent are proposed to be kept under M. mediterraneum strain LN707b and LN 7007.     

Diversity of rhizobia nodulating Lotus corniculatus grown in northern and southern regions of Uruguay

Diversity of rhizobia nodulating Lotus corniculatus grown in geographical regions with different rainfall regimes in northern and southern Uruguay, was estimated using 168 root nodule isolates. ERIC-PCR analysis revealed no correlation between observed fingerprints and the geographical origin of isolates. Despite the commercial strain U510 has been used for decades to inoculate L. corniculatus, none of the isolates corresponded to this strain. Phylogenetic analyses using 16S rRNA and atpD genes, and ITS sequences clustered all the isolates within genus Mesorhizobium. A great majority of the isolates likely belong to the species M. huakuii, as does the commercial strain U510. The remaining isolates were closely related to either M. septentrionale or M. caraganae. Although no M. loti-like bacteria were identified, all isolates carried symbiotic genes closely related to M. loti and other narrow host range Lotus rhizobia. A significant portion of the Uruguayan isolates were as efficient as the reference strain U510 in symbiosis with L. corniculatus. A few of the isolates were also capable of nitrogen fixation in symbiosis with L. uliginosus, albeit with lower efficiency than reference strains. Our results indicate that rhizobia nodulating L. corniculatus in Uruguay are genetically and phenotypically diverse, and that the commercial strain U510 is probably not adapted to survive the Uruguayan edaphoclimatic conditions.     

Genetic diversity of rhizobia associated with indigenous legumes in different regions of Flanders (Belgium)

We investigated the diversity of rhizobia isolated from different indigenous legumes in Flanders (Belgium). A total of 3810 bacterial strains were analysed originating from 43 plant species. Based on rep-PCR clustering, 16S rRNA gene and recA gene sequence analysis, these isolates belonged to Bradyrhizobium, Ensifer (Sinorhizobium), Mesorhizobium and Rhizobium. Of the genera encountered, Rhizobium was the most abundant (62%) and especially the species Rhizobiumleguminosarum, followed by Ensifer (19%), Bradyrhizobium (14%) and finally Mesorhizobium (5%). For two rep-clusters only low similarity values with other genera were found for both the 16S rRNA and recA genes, suggesting that these may represent a new genus with close relationship to Rhodopseudomonas and Bradyrhizobium. Primers for the symbiotic genes nodC and nifH were optimized and a phylogenetic sequence analysis revealed the presence of different symbiovars including genistearum, glycinearum, loti, meliloti, officinalis, trifolii and viciae. Moreover, three new nodC types were assigned to strains originating from Ononis, Robinia and Wisteria, respectively. Discriminant and MANOVA analysis confirmed the correlation of symbiosis genes with certain bacterial genera and less with the host plant. Multiple symbiovars can be present within the same host plant, suggesting the promiscuity of these plants. Moreover, the ecoregion did not contribute to the separation of the bacterial endosymbionts. Our results reveal a large diversity of rhizobia associated with indigenous legumes in Flanders. Most of the legumes harboured more than one rhizobial endosymbiont in their root nodules indicating the importance of including sufficient isolates per plant in diversity studies.     

Diversity and phylogeny of rhizobial strains isolated from Lotus uliginosus grown in Uruguayan soils

Lotus uliginosus is generally nodulated by rhizobia of the genus Bradyrhizobium when used for improvement of Uruguayan pastures. The genetic diversity and phylogenetic relationships of 111 isolates from nodules of L. uliginosus collected from four fields with or without prior inoculation history were analyzed in this study. Genetic diversity estimated by ERIC-PCR revealed 75 different genomic fingerprints, and showed a relatively greater value compared with other methods and varied by soil type. 16S ribosomal RNA gene RFLP analysis revealed three different ribogroups, A, B and C, with 71 isolates in ribogroup A, three isolates in ribogroup B and only one in ribogroup C. Phylogenetic analyses based on 16S RNA gene sequences, ITS, as well as atpD, recA and glnII gene sequences indicated that ribogroup A strains were affiliated with B. japonicum bv. genistearum strains. The three isolates in ribogroup B did not clearly associate with any Bradyrhizobium species described previously and could represent a novel species within this genus. Unlike B. japonicum strains these isolates were able to nodulate and fix nitrogen with other Lotus species as well as with Spartium, a leguminous shrub. The unique isolate in ribogroup C clustered with Mesorhizobium and appeared genetically and phenotypically related to broad host-range Mesorhizobium sp. NZP2037. Our data suggest that Uruguayan soils contain native or naturalized bradyrhizobia that are able to nodulate L. uliginosus as efficiently as the commercial strain NZP2309 but could have adaptive advantages making them more suitable for inoculant purposes.     

Compatibility of Mesorhizobium sp. Cicer with seed treatment of fungicide and insecticide in chickpea

This investigation was undertaken to study the compatibility of Mesorhizobium sp. Cicer with captan (fungicide) and chlorpyrifos (insecticide) for growth, symbiotic parameters and yield in chickpea. In an in vitro experiment, a significant reduction in the number of viable mesorhizobia was observed in Mesorhizobium sp. Cicer treated chickpea seeds at the recommended doses of captan (3 g kg^?1 seed) and chlorpyrifos (10 ml kg^?1 seed) after 4 h storage at 4°C, and further reduction was seen after 8–16 h contact with Mesorhizobium. The results showed that captan was more toxic than chlorpyrifos. In field experiments, improved growth and symbiotic parameters (plant height, dry weight of shoot, nodulation, leghaemoglobin content, chlorophyll content and nitrogen content) and a reduction in per cent damaged by termites and diseases were observed in the Mesorhizobium alone treatment compared with the uninoculated control. Grain yield was increased significantly in treatments with Mesorhizobium alone or in a mixture with fungicide and insecticide (captan and chlorpyrifos) compared with the control treatment. It is evident that chemically treated seeds should always be sown as soon as possible after inoculation. Recommended rates of captan and chlorpyrifos application with Mesorhizobium inoculant as a seed treatment was innocuous to chickpea–Mesorhizobium symbiosis.     

Genetic diversity of rhizobia associated with indigenous legumes in different regions of Flanders (Belgium)

We investigated the diversity of rhizobia isolated from different indigenous legumes in Flanders (Belgium). A total of 3810 bacterial strains were analysed originating from 43 plant species. Based on rep-PCR clustering, 16S rRNA gene and recA gene sequence analysis, these isolates belonged to Bradyrhizobium, Ensifer (Sinorhizobium), Mesorhizobium and Rhizobium. Of the genera encountered, Rhizobium was the most abundant (62%) and especially the species Rhizobium leguminosarum, followed by Ensifer (19%), Bradyrhizobium (14%) and finally Mesorhizobium (5%). For two rep-clusters only low similarity values with other genera were found for both the 16S rRNA and recA genes, suggesting that these may represent a new genus with close relationship to Rhodopseudomonas and Bradyrhizobium. Primers for the symbiotic genes nodC and nifH were optimized and a phylogenetic sequence analysis revealed the presence of different symbiovars including genistearum, glycinearum, loti, meliloti, officinalis, trifolii and viciae. Moreover, three new nodC types were assigned to strains originating from Ononis, Robinia and Wisteria, respectively. Discriminant and MANOVA analysis confirmed the correlation of symbiosis genes with certain bacterial genera and less with the host plant. Multiple symbiovars can be present within the same host plant, suggesting the promiscuity of these plants. Moreover, the ecoregion did not contribute to the separation of the bacterial endosymbionts. Our results reveal a large diversity of rhizobia associated with indigenous legumes in Flanders. Most of the legumes harboured more than one rhizobial endosymbiont in their root nodules indicating the importance of including sufficient isolates per plant in diversity studies.     

Inoculation with Phosphate Solubilizing Mesorhizobium Strains Improves the Performance of Chickpea (Cicer aritenium L.) Under Phosphorus Deficiency

The use of phosphate-solubilising bacteria as inoculants increases plant phosphorus (P) uptake and thus crop yield. Strains from the genus Mesorhizobium are among the most powerful phosphate solubilizing microorganisms. In order to study efficiency in P uptake and N₂ fixation in chickpea (Cicer aritenium), forty-two rhizobia strains natively from Tunisian soils were studied in symbiosis with the chickpea variety “Béja1” which is frequently cultivated in Tunisia. Plants were inoculated separately with these strains under controlled conditions in perlite under two sources of P i.e. soluble (KH₂PO₄) and insoluble P (Ca₂HPO₄). At flowering stage, growth, nodulation, P uptake and N₂ fixation were assessed in all symbiotic combinations. The results showed that the S27 strain efficiently mobilized P into plants, observed as a significant increase of plant P content when insoluble P (Ca₂HPO₄) was supplied to the soil. This was associated with a significant increase in plant biomass, nodule number and N content under insoluble P conditions. Additionally, inoculation with the Mesorhizobium strain S27 significantly increased the root acid phosphatase activity under insoluble P. This study also shows significant correlations found between plant P content and acid phosphatase activity under low P conditions which may highlight the contribution of acid phosphatases in increasing P use efficiency. A field experiment also showed that most of the chickpea analyzed parameters were improved when plants inoculated with two selected rhizobia strains (S26 and S27) and supplied with P2O5. Overall, these findings postulate that rhizobial inoculation should not only be based on the effectiveness of strains regarding N fixation, but also to other traits such as P solubilisation potential.     

Isolation and identification of oxamyl-degrading bacteria from UK agricultural soils

Bacteria capable of utilising oxamyl as the sole carbon source were isolated from seven different agricultural soils that had previously demonstrated enhanced oxamyl degradation in a soil incubation study. Partial sequencing and alignment of the 16S rRNA gene showed little diversity amongst isolates, with 26 of the 27 isolates demonstrating similarity to the genus Aminobacter. The most common species isolated was Aminobacter aminovorans, while a number of the isolates demonstrated an equal degree of similarity to the species Aminobacter niigataensis and Chelatobacter heintzii. One isolate was identified as Mesorhizobium sp. This is the first time that organisms involved in the degradation of oxamyl have been isolated and identified.     

Symbiotic nitrogen contribution and biodiversity of root-nodule bacteria nodulating Psoralea species in the Cape Fynbos,South Africa

The genus Psoralea (tribe Psoraleae, family Leguminosae) is indigenous to the Cape fynbos of South Africa and little is known about its symbiosis and/or adaptation. The aim of this study was to assess root nodulation and N₂ fixation in eight of the 50 Psoralea species, as well as the biodiversity of their associated nodulating microsymbionts. The eight species studied (namely, Psoralea pinnata, Psoralea aphylla, Psoralea aculeata, Psoralea monophylla, Psoralea repens, Psoralea laxa, Psoralea asarina and Psoralea restioides) all had round-shaped, determinate type (desmodioid) nodules, and data from ¹⁵N natural abundance showed that they obtained 60–88% of their N nutrition from symbiotic fixation. These Psoralea species also transported their fixed-N as ureides (allantoin and allantoic acid) in the xylem stream, a symbiotic trait that links them very closely to the tribe Phaseoleae. Bacteria isolated from root nodules of the eight Psoralea species varied in phenotypic characteristics, nodulation promiscuity, and N₂-fixing efficacy. Furthermore, 16S rDNA gene sequence data showed that Psoralea species can form root nodules with different soil bacteria, including Rhizobium, Mesorhizobium and Burkholderia strains. This is not only evidence of nodulation promiscuity, but also an indication of the species’ adaptation to the nutrient-poor, low-N, sandy acidic soils of the Cape fynbos.     

Genetic diversity and symbiotic efficiency of rhizobial isolates obtained from nodules of Arachis hypogaea in northwestern Morocco

The molecular characterization of 62 rhizobial isolates obtained from root-nodules of Arachis hypogaea growing in north-western Morocco was performed. Bacteria were firstly characterized by restriction of the 16S-rDNA region, and phylogeny was inferred from 16S gene sequences. Phylogenetically, isolates were grouped with species belonging to the Bradyrhizobium and Rhizobium genera. A high degree of variability was detected among isolates in terms of their nitrogen-fixing ability. This is, to our knowledge, the first study on genetic diversity and symbiotic effectiveness of rhizobia isolated from peanut nodules grown in Morocco. This characterization provides a basis for the selection of peanut-nodulating rhizobia which may have applications in the formulation of appropriate inocula to improve peanut crop yield on Moroccan soils.     

Genotypic diversity and symbiotic effectiveness of rhizobia isolated from root nodules of Phaseolus vulgaris L. grown in Tunisian soils

 One hundred and sixty isolates of rhizobia were sampled from the root nodules of common bean (Phaseolus vulgaris L.) cultivated in Tunisian soil samples originating from three geographically distinct fields. Plasmid profiling was used as a primary method to rapidly screen the isolates, and then 38 plasmid types were recorded among the 160 isolates. A sample representing the majority of plasmid types was chosen for further characterization by restriction fragment length polymorphism (RFLP) analysis of genomic DNA using chromosomal and symbiotic gene probes, and by their ability to nodulate a potential alternative host, Leucaena leucocephala. One third of the isolates showed a high similarity to Rhizobium gallicum isolated from common bean in France, another third showed the same characteristics as the R. etli-R. leguminosarum group, while the remaining isolates could not be related to any of the five species nodulating bean. When reexamined for nodulation, some of these isolates, showing similarities to R. tropici and Agrobacterium with respect to colony morphology and growth in different media, failed to nodulate their original host. The R. gallicum-like isolates, R. etli-like isolates, and R. leguminosarum-like isolates were recovered from regions where bean is frequently grown, while in fields which had not been cultivated with beans for at least the 10 previous years, solely unrecognized taxa of ineffective isolates were recovered. We detected variations in the symbiotic regions, but certain pSym RFLP patterns for nifH were conserved between Tunisian, French, and Austrian populations of bean rhizobia. Evaluation of symbiotic effectiveness showed that R. gallicum-like isolates and R. etli-like isolates were effective, whereas some R. leguminosarum-like isolates were ineffective. Furthermore, effective isolates were also found among the unrecognized taxa. Received: 10 March 1998     

<Emphasis Type="Italic">Rhizobium</Emphasis>,<Emphasis Type="Italic"> Bradyrhizobium</Emphasis> and<Emphasis Type="Italic"> Agrobacterium</Emphasis> strains isolated from cultivated legumes

The present study was conducted to isolate and characterize rhizobial strains from root nodules of cultivated legumes, i.e. chickpea, mungbean, pea and siratro. Preliminary characterization of these isolates was done on the basis of plant infectivity test, acetylene reduction assay, C-source utilization, phosphate solubilization, phytohormones and polysaccharide production. The plant infectivity test and acetylene reduction assay showed effective root nodule formation by all the isolates on their respective hosts, except for chickpea isolate Ca-18 that failed to infect its original host. All strains showed homology to a typical Rhizobium strain on the basis of growth pattern, C-source utilization and polysaccharide production. The strain Ca-18 was characterized by its phosphate solubilization and indole acetic acid (IAA) production. The genetic relationship of the six rhizobial strains was carried out by random amplified polymorphic DNA (RAPD) including a reference strain of Bradyrhizobium japonicum TAL-102. Analysis conducted with 60 primers discriminated between the strains of Rhizobium and Bradyrhizobium in two different clusters. One of the primers, OPB-5, yielded a unique RAPD pattern for the six strains and well discriminated the non-nodulating chickpea isolate Ca-18 from all the other nodulating rhizobial strains. Isolate Ca-18 showed the least homology of 15% and 18% with Rhizobium and Bradyrhizobium, respectively, and was probably not a (Brady)rhizobium strain. Partial 16S rRNA gene sequence analysis for MN-S, TAL-102 and Ca-18 strains showed 97% homology between MN-S and TAL-102 strains, supporting the view that they were strains of B. japonicum species. The non-infective isolate Ca-18 was 67% different from the other two strains and probably was an Agrobacterium strain.     

Co-introduction of exotic rhizobia to the rhizosphere of the invasive legume Acacia saligna,an intercontinental study

Invasive woody legumes have profound impacts in the nitrogen content and cycling of invaded ecosystems due to the ability to enter into symbiosis with nitrogen-fixing bacteria. In spite of the relevance of this symbiosis, the identity and origin of the symbionts involved in invasion are not well understood. We conducted a study to assess the diversity of symbiotic root-nodulating bacteria associated with the invasive Acacia saligna, in newly colonized areas in Portugal and Australia. BOX-PCR was used to discriminate the isolated bacteria and 16S rRNA and nifD genes were sequenced to identify the different isolates and their geographic origin. Bradyrhizobium and Mesorhizobium nodulated A. saligna in Australia while only Bradyrhizobium spp. were found in Portugal. The dominant strains nodulating A. saligna were related to Bradyrhizobium liaoningense and Bradyrhizobium canariense. Co-occurring Acacia longifolia and A. saligna in Australia harbor different rhizobial communities. As an example, we found Mesorhizobium sp. and Phyllobacterium trifolii in A. saligna and A. longifolia respectively, being this the first report for this association. The analysis of the phylogeographic marker nifD clustered most of the sequences obtained in this study with sequences of Australian origin, indicating that exotic bradyrhizobia might have been co-introduced with A. saligna in Portugal. This result highlights the risks of introducing exotic inoculants that might facilitate the invasion of new areas and alter native soil bacterial communities, hindering the recovery of ecosystems.     

Distribution and genetic diversity of rhizobia nodulating natural populations of Medicago truncatula in tunisian soils

A collection of 299 isolates of rhizobia nodulating Medicago truncatula was isolated from 10 Tunisian soils and was characterized by restriction fragment length polymorphism analysis of polymerase chain reaction (PCR/RFLP) of 16S rRNA gene. Results showed that 227 and 72 isolates were assigned, respectively, to Sinorhizobium meliloti and Sinorhizobium medicae. In 9 out of 10 soils S. meliloti was detected, whereas S. medicae was recovered from only 5 out of 10 soils. The cross-nodulation of three populations of M. truncatula grown on Bulla Regia soil, which contained naturally the two Sinorhizobium species, showed that M. truncatula population collected from Amra site was selective to S. meliloti at least in soil conditions. Forty-eight isolates of each Sinorhizobium species trapped by M. truncatula populations collected from Bulla Regia, Soliman and Rhayet sites on Bulla Regia soil were characterized by repetitive extragenic palindromic-PCR (REP-PCR) and showed a clear distinction between the two Sinorhizobium species and a higher diversity for S. meliloti.     

Impact of single and co-inoculations with Rhizobial and PGPR isolates on chickpea (Cicer arietinum) in cereal-growing zone soil

Strains isolated from chickpea (Cicer arietinum L.) rhizospheric soil from selected sites in Algeria were screened for their plant-growth-promoting potential, for indole acetic acid production and P solubilization ability. Then, we selected native rhizobial strains with high nitrogen-fixing potential. On the basis of their efficiency under controlled conditions, two plant-growth-promoting rhizobacteria (PGPR) isolates and three nodulating bacteria were selected. Then, the effect of single PGPR isolates inoculation was compared to their combination with rhizobial inoculants on plant growth, on native cereal-growing soils under greenhouse conditions. No effects were observed on chickpea yield by using rhizobial inoculation alone, nor by PGPR-rhizobial co-inoculation on two soils presenting weak and no nodulation pattern in natural conditions. Only PGPR inoculation improved growth of plants on soil with no nodulation pattern. These findings emphasized inoculation on native soils at a little scale before large assays on field because no one could predict inocula behavior with native soil microflora.     

Polyphasic characterization of mung bean (Vigna radiata L.) rhizobia from different geographical regions of China

Polyphasic characterization of 54 indigenous mung bean (Vigna radiata L.) rhizobia from different geographic regions of China was determined by analyzing the variability of 16S rRNA gene RFLP, 16S–23S rRNA gene Intergenetic Spacer (IGS) RFLP, G-C rich RAPD and phenotype assays. Based on these characteristics, mung bean rhizobia were clustered into four groups. Group I comprised 16 slow-growing isolates from a variety of geographic regions. This group was genetically distinct from Bradyrhizobium japonicum and Bradyrhizobium liaoningense, and may represent a new species. Group II was composed of 18 isolates, which could be sub-divided into two sub-groups that were respectively related to B. japonicum and B. liaoningense. Group III comprised 12 isolates from South China and clustered together with Bradyrhizobium elkanii. Group IV formed a miscellany of 8 fast-growing isolates variously related to the genera Sinorhizobium, Rhizobium and Mesorhizobium.     

Characterization of rhizobia from <Emphasis Type="Italic">Sesbania</Emphasis> species native to seasonally wetland areas in Uruguay

Naturally growing Sesbania species with tolerance to unfavourable habitats are widely distributed in non-cultivated seasonally wetland areas in Uruguay. We investigated the relative abundance, diversity and symbiotic efficiency of Sesbania punicea and S. virgata rhizobia in three ecologically different undisturbed and water-logged sites in Uruguay. Numbers of native-soil rhizobia infective on S. punicea or S. virgata were low, with higher numbers associated with the presence of S. virgata. Plants of S. virgata inoculated with soil suspension showed aerial and nodule biomass greater than that obtained with S. punicea. The rhizobia nodulating Sesbania species in water-logged lands in different regions of Uruguay were diverse differing in growth rates, acid production, growth at 39°C and in LB medium, host range and symbiotic efficiency. Seventeen representative strains clustered into four groups on the basis of phenotypic characteristics, ARDRA and DNA fingerprinting (GTG₅-PCR). Partial sequence of 16S rRNA from eight of these strains classified them into at least two genera with four species: Azorhizobium doebereinerae, Rhizobium sp. related to R. etli and two different Rhizobium sp.-Agrobacterium. Our results confirm the presence of the specie Azorhizobium doebereinerae as microsymbionts of S. virgata in South America. No strain of Rhizobium etli has previously been reported as a microsymbiont of Sesbania, though R. etli like organisms have also been recovered from Dalea purpurea and Desmanthus illinoensis. Significant increases in dry matter production were obtained with S. virgata plants inoculated with selected rhizobial strains under growth chamber conditions.     

Identification of an Organism Associated with Mushroom Worker's Lung

Saccaromonospora viridis is a thermophilic actinomycetes organism which is found in mushroom compost, as well as being a causal agent of mushroom worker's lung (MWL) and other hypersensitivity pneumonitis conditions, including farmer's lung. Phenotypically, it is difficult to distinguish the seven species described for this genus based solely on chemtaxonomic characterization, therefore it was the aim of this study to examine partial 16S rDNA PCR amplification and direct sequencing, as an improved molecular means of identification of Saccharomonospora viridis, associated with MWL. The approach adopted in this study was to identify hypervariable regions within the 16S rRNA gene, which could be employed as signature sequences of the seven individual species within this genus and to employ highly conserved flanking primers to allow initial PCR amplification, prior to direct DNA sequencing of the 16S rDNA amplicon, in a partial 16S rDNA-sequence typing technique. Four universal 16S rDNA primer combinations [P11P/P13P, PSL/PSR, XB1(SV)/PSR and XB1(SV)/P13P] were compared for their ability to identify an unknown thermophilic Saccharomonospora organism from MWL. All PCR primer combinations coupled with direct sequencing allowed for the successful identification of the MWL isolate as S. viridis, demonstrating that universal 16S rDNA PCR primer pairs examined, including the P11P/P13P primer pair, flank regions within the 16S rRNA gene, of sufficient hypervariability to be able to reliably differentiate S. viridis from the other species within this genus. This approach may therefore be useful in the identification of Saccharomonospora spp. associated with composting, as well as with allergic alveolitis or pneumonitis associated occupational exposure in agricultural and horticultural environments, including mushroom production.     

Molecular and physiological characterisation of psychrotrophic hydrocarbon-degrading bacteria isolated from Terra Nova Bay (Antarctica)

A set of 21 Antarctic marine bacteria isolated from the Ross Sea and able to utilise diesel fuel as the sole carbon and energy source was characterised. Isolates were analysed by amplified 16S rDNA restriction analysis using the enzyme AluI, resulting in two different groups corresponding to different bacterial species. These species were assigned to the genera Rhodococcus and Alcaligenes, on the basis of 16S rDNA sequencing. This low degree of inter-specific biodiversity was parallel to a low intra-specific biodiversity, as shown by Random Amplified Polymorphic DNA analysis. Then, a 550-bp DNA fragment coding for the inner region of alkane mono-oxygenase was PCR-amplified from the genome of each strain. The phylogenetic analysis of the sequence of the putative AlkB protein coded for by the amplified DNA fragment revealed that these alkB genes were very likely inherited by horizontal gene transfer. Lastly, the analysis of the biodegradation ability of four strains revealed two different strategies of hydrocarbon uptake, mediated either by bio-surfactants and peculiar of Rhodococcus isolates, or by membrane modifications and shown by Alcaligenes isolates. In order to understand the interrelationships between hydrocarbon-degrading isolates, the dynamics of two strains, belonging to Rhodococcus and Alcaligenes, grown together in a co-culture was also followed over a seventeen days period.     

Enhancement of Nodulation and Yield of Chickpea by Co-inoculation of Indigenous Mesorhizobium spp. and Plant Growth–Promoting Rhizobacteria in Eastern Uttar Pradesh

We study the effect of plant growth–promoting rhizobacteria (PGPR) along with Mesorhizobium sp. BHURC02 on nodulation, plant growth, yield, and nutrient content of chickpea (Cicer arietinum L.) under field conditions. A similar study has been conducted for nodulation and plant growth of chickpea in pot experiment under glasshouse conditions. The treatment combination of Mesorhizobium sp. BHURC02 and Pseudomonas fluorescens BHUPSB06 statistically significantly increased nodule number plant^–1, dry weight of nodule plant^–1, and root and shoot dry weights plant^–1 over the control under a glasshouse experiment. The maximum significant increase in nodule number, dry matter, and nutrient content were recorded in co-inoculation of Mesorhizobium sp. BHURC02 and P. fluorescens BHUPSB06 followed by co-inoculation of Mesorhizobium sp., Azotobacter chroococcum, and Bacillus megatrium BHUPSB14 over uninoculated control in a 2-year field study. Hence, co-inoculation of Mesorhizobium sp. and P. fluorescens may be effective indigenous PGPR for chickpea production.