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Ensifer sp. PC2 is an aerobic, motile, Gram-negative, non-spore-forming rod that was isolated from a nitrogen-fixing nodule of the tree legume P. cineraria (L.) Druce (Khejri), which is a keystone species that grows in arid and semi-arid regions of the Indian Thar desert. Strain PC2 exists as a dominant saprophyte in alkaline soils of Western Rajasthan. It is fast growing, well-adapted to arid conditions and is able to form an effective symbiosis with several annual crop legumes as well as species of mimosoid trees and shrubs. Here we describe the features of Ensifer sp. PC2, together with genome sequence information and its annotation. The 8,458,965 bp high-quality permanent draft genome is arranged into 171 scaffolds of 171 contigs containing 8,344 protein-coding genes and 139 RNA-only encoding genes, and is one of the rhizobial genomes sequenced as part of the DOE Joint Genome Institute 2010 Genomic Encyclopedia for Bacteria and Archaea-Root Nodule Bacteria (GEBA-RNB) project proposal. [ABSTRACT FROM AUTHOR]

Ensifer sp. TW10 is a novel N-fixing bacterium isolated from a root nodule of the perennial legume Tephrosia wallichii Graham (known locally as Biyani) found in the Great Indian (or Thar) desert, a large arid region in the northwestern part of the Indian subcontinent. Strain TW10 is a Gram-negative, rod shaped, aerobic, motile, non-spore forming, species of root nodule bacteria (RNB) that promiscuously nodulates legumes in Thar Desert alkaline soil. It is fast growing, acid-producing, and tolerates up to 2% NaCl and capable of growth at 40C. In this report we describe for the first time the primary features of this Thar Desert soil saprophyte together with genome sequence information and annotation. The 6,802,256 bp genome has a GC content of 62% and is arranged into 57 scaffolds containing 6,470 protein-coding genes, 73 RNA genes and a single rRNA operon. This genome is one of 100 RNB genomes sequenced as part of the DOE Joint Genome Institute 2010 Genomic Encyclopedia for Bacteria and Archaea-Root Nodule Bacteria (GEBA-RNB) project. [ABSTRACT FROM AUTHOR]

Background and Aims The large monophyletic genus Mimosa comprises approx. 500 species, most of which are native to the New World, with Central Brazil being the main centre of radiation. All Brazilian Mimosa spp. so far examined are nodulated by rhizobia in the betaproteobacterial genus Burkholderia. Approximately 10 Mya, transoceanic dispersal resulted in the Indian subcontinent hosting up to six endemic Mimosa spp. The nodulation ability and rhizobial symbionts of two of these, M. hamata and M. himalayana, both from north-west India, are here examined, and compared with those of M. pudica, an invasive species. Methods Nodules were collected from several locations, and examined by light and electron microscopy. Rhizobia isolated from them were characterized in terms of their abilities to nodulate the three Mimosa hosts. The molecular phylogenetic relationships of the rhizobia were determined by analysis of 16S rRNA, nifH and nodA gene sequences. Key Results Both native Indian Mimosa spp. nodulated effectively in their respective rhizosphere soils. Based on 16S rRNA, nifH and nodA sequences, their symbionts were identified as belonging to the alphaproteobacterial genus Ensifer, and were closest to the ‘Old World’ Ensifer saheli, E. kostiensis and E. arboris. In contrast, the invasive M. pudica was predominantly nodulated by Betaproteobacteria in the genera Cupriavidus and Burkholderia. All rhizobial strains tested effectively nodulated their original hosts, but the symbionts of the native species could not nodulate M. pudica. Conclusions The native Mimosa spp. in India are not nodulated by the Burkholderia symbionts of their South American relatives, but by a unique group of alpha-rhizobial microsymbionts that are closely related to the ‘local’ Old World Ensifer symbionts of other mimosoid legumes in north-west India. They appear not to share symbionts with the invasive M. pudica, symbionts of which are mostly beta-rhizobial. [ABSTRACT FROM PUBLISHER]

Aims: To survey the occurrence of nodulated legumes in the arid and semi-arid areas of Western Rajasthan and to characterize their associated symbiotic bacteria. Methods: Herbaceous annual species were excavated whole, while tree species were studied as seedlings in the field or as trap plants in pot experiments. Nodules were examined by microscopy to confirm their effectiveness and to determine their internal structure. Bacteria isolated from the nodules were authenticated on their original hosts and were identified on the basis of 16S rRNA sequencing. Phylogenetic trees were inferred using the neighbour-joining method. Results: We studied 35 of more than 50 species of native legume reported from these areas. Legumes are drought escaping (annual species), drought tolerant perennials or trees possessing deep root systems and other adaptations to arid conditions. Nodulation was recorded in all members of the Papilionoideae and Mimosoideae, but only one species of Caesalpinioideae. Internal structure of nodules varied within these groups, especially with respect to the presence or absence of uninfected cells in the infected region. Full 16S rRNA gene sequencing revealed that the nodules harboured a range of nodulating bacteria belonging to the genera Sinorhizobium, Rhizobium and Bradyrhizobium, within which they formed separate sub clades. Conclusions: This study extends the range of legumes known to grow and nodulate in semi-arid regions, and provides information about their endosymbionts. [ABSTRACT FROM AUTHOR]

Arid and semi-arid areas occupy an increasing fraction of the Earth's surface. Legume floras exist for most of these areas, but there is little information as to whether the plants nodulate and fix nitrogen (N) in their native habitats, although many have been used over millennia for food, forage and medicinal and other uses. This review shows that, in those arid and semi-arid areas where data are available, the ability of legumes to nodulate is a significant attribute. It examines some host genera present and, where known, the bacteria that induce nodulation in them. With some exceptions all legumes from well-studied arid areas have the potential to nodulate. Semi-arid areas vary between continents in terms of legume genera present, the probable extent of N fixation and in the endosymbionts (rhizobia) that induce nodulation in them. With climate change and an increasing world population, there is an urgent need to develop the diverse range of nodulated legumes native to dry environments. With modern methods this goal is readily achievable. [ABSTRACT FROM AUTHOR]

Sesamum indicum is an important oil seed crop of semi-arid regions. Recently released cultivars of S. indicum were evaluated for their relative tolerance to sodium chloride (NaCl) salt. Salinity induced alterations in electrophoretic patterns of proteins and other metabolites were recorded in seeds germinated and grown in presence of different concentrations of sodium chloride (0.30, 50 and 70mM). Seedling growth was retarded in cv. RT-125 in presence of NaCl more than 30mM concentration. Control seedlings of cv. RT-46, RT-54 and RT-127 showed higher levels of total soluble sugars and sucrose as compared to cv. RT-125. Proline contents of control seedlings of cv. RT-127 was low as compared to other cultivars. Levels of soluble proteins were higher in RT-I25 and RT-127 than in RT-46 and RT-54 under all experimental conditions. However levels of sugars were higher in salt-treated cvs.RT-127. RT-46 and RT-54 as compared lo RT-125. Salt sensitive cultivar (RT-125), accumulated higher contents of malondialdehyde (MDA) and proline as compared to the others. On the other hand salt tolerant cultivars RT-54, RT-46 and RT-127 showed higher activity of superoxide-dismutase (SOD) and low MDA content as compared to RT-125. [ABSTRACT FROM AUTHOR]

Background: Nitrogen fixing bacteria isolated from hot arid areas in Asia, Africa and America but from diverse leguminous plants have been recently identified as belonging to a possible new species of Ensifer (Sinorhizobium). In this study, 6 strains belonging to this new clade were compared with Ensifer species at the genome-wide level. Their capacities to utilize various carbon sources and to establish a symbiotic interaction with several leguminous plants were examined. Results: Draft genomes of selected strains isolated from Morocco (Merzouga desert), Mexico (Baja California) as well as from India (Thar desert) were produced. Genome based species delineation tools demonstrated that they belong to a new species of Ensifer. Comparison of its core genome with those of E. meliloti, E. medicae and E. fredii enabled the identification of a species conserved gene set. Predicted functions of associated proteins and pathway reconstruction revealed notably the presence of transport systems for octopine/nopaline and inositol phosphates. Phenotypic characterization of this new desert rhizobium species showed that it was capable to utilize malonate, to grow at 48 °C or under high pH while NaCl tolerance levels were comparable to other Ensifer species. Analysis of accessory genomes and plasmid profiling demonstrated the presence of large plasmids that varied in size from strain to strain. As symbiotic functions were found in the accessory genomes, the differences in symbiotic interactions between strains may be well related to the difference in plasmid content that could explain the different legumes with which they can develop the symbiosis. Conclusions: The genomic analysis performed here confirms that the selected rhizobial strains isolated from desert regions in three continents belong to a new species. As until now only recovered from such harsh environment, we propose to name it Ensifer aridi. The presented genomic data offers a good basis to explore adaptations and functionalities that enable them to adapt to alkalinity, low water potential, salt and high temperature stresses. Finally, given the original phylogeographic distribution and the different hosts with which it can develop a beneficial symbiotic interaction, Ensifer aridi may provide new biotechnological opportunities for degraded land restoration initiatives in the future. [ABSTRACT FROM AUTHOR]

Summary: Nitrogen‐fixing symbiosis is globally important in ecosystem functioning and agriculture, yet the evolutionary history of nodulation remains the focus of considerable debate. Recent evidence suggesting a single origin of nodulation followed by massive parallel evolutionary losses raises questions about why a few lineages in the N2‐fixing clade retained nodulation and diversified as stable nodulators, while most did not. Within legumes, nodulation is restricted to the two most diverse subfamilies, Papilionoideae and Caesalpinioideae, which show stable retention of nodulation across their core clades.We characterize two nodule anatomy types across 128 species in 56 of the 152 genera of the legume subfamily Caesalpinioideae: fixation thread nodules (FTs), where nitrogen‐fixing bacteroids are retained within the apoplast in modified infection threads, and symbiosomes, where rhizobia are symplastically internalized in the host cell cytoplasm within membrane‐bound symbiosomes (SYMs).Using a robust phylogenomic tree based on 997 genes from 147 Caesalpinioideae genera, we show that losses of nodulation are more prevalent in lineages with FTs than those with SYMs.We propose that evolution of the symbiosome allows for a more intimate and enduring symbiosis through tighter compartmentalization of their rhizobial microsymbionts, resulting in greater evolutionary stability of nodulation across this species‐rich pantropical legume clade. [ABSTRACT FROM AUTHOR]

More than 200 root-nodule bacterial strains were isolated from Leucaena leucocephala growing at 42 sampling sites across 12 states and three union territories of India. Genetic diversity was observed among 114 strains from various climatic zones; based on recA , these were identified as strains of Ensifer , Mesorhizobium , Rhizobium , and Bradyrhizobium. In multilocus sequence analysis (MLSA) strains clustered into several novel clades and lineages. Ensifer were predominant nodulating genotype isolated from majority of alkaline soils, while Mesorhizobium and Rhizobium strains were isolated from a limited sampling in North-Eastern states with acidic soils. Positive nodulation assays of selected Ensifer representing different genetic combinations of housekeeping and sym genes suggested their broad host range within the closely related mimosoid genera Vachellia , Senegalia , Mimosa , and Prosopis. Leucaena selected diverse strains of Ensifer and Mesorhizobium as symbionts depending on available soil pH, climatic, and other edaphic conditions in India. Lateral gene transfer seems to play a major role in genetic diversification of Ensifer exhibited in terms of Old World vs. Neotropical genetic make-up and mixed populations at several sites. Although Neotropical Ensifer strains were most symbiotically effective on Leucaena , the native Ensifer are promiscuous and particularly well-adapted to a wide range of sampling sites with varied climates and edaphic factors. [ABSTRACT FROM AUTHOR]

In order to survive at temperatures of ≥60°C, thermophilic prokaryotes (Archaea and Eubacteria) have adopted different strategies. These strategies include high CG content in the coding sequences, nucleotide arrangement of purine-purine and pyrimidine-pyrimidine, methylation of nucleotides, histone/histone like proteins, reverse gyrase, cations, etc., also provide thermal stability to genome. Strategies adopted at the level of DNA are naturally, though not universally, reflected in RNA in thermophiles. Increased purine load (particularly of adenine), preferential codon usage, post-transcriptional modifications etc. provide thermal stability. All these factors may differ from taxa to taxa as no single or all the factors together can be universally attributed for providing thermal stability to nucleic acids. [ABSTRACT FROM AUTHOR]

Aims: To describe the structure of nodules of Vachellia ( Acacia) jacquemontii, and to characterise the rhizobia that occupy them. Methods: Light and electron microscopy were used to analyse nodules. Rhizobia were characterised using their 16S rRNA, housekeeping and symbiosis-related gene sequences. Results: Nodules of V. jacquemontii were typical of all other described mimosoid legumes. All 73 of the isolates were strains of Ensifer, and concatenated phylogenetic analysis of their housekeeping genes ( rrs, recA, atpD, glnII and dnaK) suggested that they are novel, forming separate lineages close to E. saheli. The phylogenies of the symbiosis-essential genes nodA and nifH were inconsistent with the housekeeping phylogenies. The nodA sequences of most isolates were close to that of E. arboris HAMBI 1552, but the nifH gene was found to be related to that of E. kostiensis HAMBI 1489. All the tested Ensifer strains, except for AJ24, were found to be capable of nodulating other species of Vachellia as well as native Indian Mimosa and Prosopis spp. Conclusions: Stressful conditions caused by the alkaline soil of the Thar Desert have resulted in V. jacquemontii being nodulated by diverse and promiscuous Ensifer species that are capable of nodulating other native members of the tribe Mimoseae. [ABSTRACT FROM AUTHOR]