ORCID Profile
0000-0003-4306-3346
Current Organisation
Murdoch University
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Publisher: Springer Science and Business Media LLC
Date: 03-02-2023
DOI: 10.1007/S11104-023-05903-0
Abstract: Inoculation of legumes with effective N 2 -fixing rhizobia is a common practice to improve farming profitability and sustainability. To succeed, inoculant rhizobia must overcome competition for nodulation by resident soil rhizobia that fix N 2 ineffectively. In Kenya, where Phaseolus vulgaris (common bean) is inoculated with highly effective Rhizobium tropici CIAT899 from Colombia, response to inoculation is low, possibly due to competition from ineffective resident soil rhizobia. Here, we evaluate the competitiveness of CIAT899 against erse rhizobia isolated from cultivated Kenyan P. vulgaris . The ability of 28 Kenyan P. vulgaris strains to nodulate this host when co-inoculated with CIAT899 was assessed. Rhizosphere competence of a subset of strains and the ability of seed inoculated CIAT899 to nodulate P. vulgaris when sown into soil with pre-existing populations of rhizobia was analyzed. Competitiveness varied widely, with only 27% of the test strains more competitive than CIAT899 at nodulating P. vulgaris . While competitiveness did not correlate with symbiotic effectiveness, five strains were competitive against CIAT899 and symbiotically effective. In contrast, rhizosphere competence strongly correlated with competitiveness. Soil rhizobia had a position-dependent numerical advantage, outcompeting seed-inoculated CIAT899 for nodulation of P. vulgaris, unless the resident strain was poorly competitive. Suboptimally effective rhizobia can outcompete CIAT899 for nodulation of P. vulgaris . If these strains are widespread in Kenyan soils, they may largely explain the poor response to inoculation. The five competitive and effective strains characterized here are candidates for inoculant development and may prove better adapted to Kenyan conditions than CIAT899.
Publisher: American Society for Microbiology
Date: 15-10-2016
DOI: 10.1128/JB.00451-16
Abstract: Within legume root nodules, rhizobia differentiate into bacteroids that oxidize host-derived dicarboxylic acids, which is assumed to occur via the tricarboxylic acid (TCA) cycle to generate NAD(P)H for reduction of N 2 . Metabolic flux analysis of laboratory-grown Rhizobium leguminosarum showed that the flux from [ 13 C]succinate was consistent with respiration of an obligate aerobe growing on a TCA cycle intermediate as the sole carbon source. However, the instability of fragile pea bacteroids prevented their steady-state labeling under N 2 -fixing conditions. Therefore, comparative metabolomic profiling was used to compare free-living R. leguminosarum with pea bacteroids. While the TCA cycle was shown to be essential for maximal rates of N 2 fixation, levels of pyruvate (5.5-fold reduced), acetyl coenzyme A (acetyl-CoA 50-fold reduced), free coenzyme A (33-fold reduced), and citrate (4.5-fold reduced) were much lower in bacteroids. Instead of completely oxidizing acetyl-CoA, pea bacteroids channel it into both lipid and the lipid-like polymer poly-β-hydroxybutyrate (PHB), the latter via a type III PHB synthase that is active only in bacteroids. Lipogenesis may be a fundamental requirement of the redox poise of electron donation to N 2 in all legume nodules. Direct reduction by NAD(P)H of the likely electron donors for nitrogenase, such as ferredoxin, is inconsistent with their redox potentials. Instead, bacteroids must balance the production of NAD(P)H from oxidation of acetyl-CoA in the TCA cycle with its storage in PHB and lipids. IMPORTANCE Biological nitrogen fixation by symbiotic bacteria (rhizobia) in legume root nodules is an energy-expensive process. Within legume root nodules, rhizobia differentiate into bacteroids that oxidize host-derived dicarboxylic acids, which is assumed to occur via the TCA cycle to generate NAD(P)H for reduction of N 2 . However, direct reduction of the likely electron donors for nitrogenase, such as ferredoxin, is inconsistent with their redox potentials. Instead, bacteroids must balance oxidation of plant-derived dicarboxylates in the TCA cycle with lipid synthesis. Pea bacteroids channel acetyl-CoA into both lipid and the lipid-like polymer poly-β-hydroxybutyrate, the latter via a type II PHB synthase. Lipogenesis is likely to be a fundamental requirement of the redox poise of electron donation to N 2 in all legume nodules.
Publisher: Wiley
Date: 14-04-2008
DOI: 10.1111/J.1469-8137.2008.02464.X
Abstract: DOI: 10.1111/j.1469-8137.2008.02494.x
Publisher: Springer Science and Business Media LLC
Date: 30-01-2018
Abstract: Rhizobia are some of the best-studied plant microbiota. These oligotrophic Alphaproteobacteria or Betaproteobacteria form symbioses with their legume hosts. Rhizobia must exist in soil and compete with other members of the microbiota before infecting legumes and forming N
Publisher: Elsevier BV
Date: 07-2018
Publisher: American Society for Microbiology
Date: 19-09-2023
DOI: 10.1128/MRA.00489-23
Abstract: We report the complete genome sequence of Rhizobium leguminosarum bv. viciae SRDI969, an acid-tolerant, efficient nitrogen-fixing microorganism of Vicia faba . The 6.8 Mbp genome consists of a chromosome and four plasmids, with the symbiosis and nitrogen fixation genes encoded on the chromosome.
Publisher: Oxford University Press (OUP)
Date: 11-05-2017
DOI: 10.1104/PP.16.01302
Publisher: Wiley
Date: 16-02-2021
DOI: 10.1111/GFS.12518
Publisher: Proceedings of the National Academy of Sciences
Date: 12-10-2016
Abstract: Integrative and conjugative elements (ICEs) are one of the most prevalent but least-characterized families of mobile genetic elements in bacteria. We identified a family of ICEs that exists as three separate parts integrated within the single chromosomes of symbiotic mesorhizobia. These “tripartite ICEs,” through a series of chromosomal recombinations mediated by integrase proteins, assemble into a single circular ICE. Following transfer to nonsymbiotic mesorhizobia, tripartite ICEs integrate and disassemble into three parts in the recipient genome and exconjugant mesorhizobia gain the ability to form a symbiosis with legumes. These discoveries expand our appreciation of the potential for gene transfer in bacteria and demonstrate how mobile genetic elements can dramatically manipulate the bacterial genome.
Publisher: American Society for Microbiology
Date: 12-02-2021
DOI: 10.1128/AEM.02558-20
Abstract: Symbiotic N 2 fixation is a key component of sustainable agriculture, and in many parts of the world legumes are inoculated with highly efficient strains of rhizobia to maximize fixed N 2 inputs into farming systems. Symbiosis genes for Mesorhizobium spp. are often carried chromosomally within mobile gene clusters called ICEs.
Publisher: American Society for Microbiology
Date: 31-08-2017
Abstract: We report here the complete genome sequence of Mesorhizobium ciceri bv. biserrulae strain WSM1497, the efficient nitrogen-fixing microsymbiont and commercial inoculant in Australia of the forage legume Biserrula pelecinus . The genome consists of 7.2 Mb distributed across a single chromosome (6.67 Mb) and a single plasmid (0.53 Mb).
Publisher: American Association for the Advancement of Science (AAAS)
Date: 30-07-2021
Abstract: Catabolism of dicarboxylates at low oxygen drives N 2 fixation and promotes ammonia secretion in rhizobium-legume symbioses.
Publisher: American Society for Microbiology
Date: 10-2010
DOI: 10.1128/JB.00294-10
Abstract: Nitrogen fixation in legume bacteroids is energized by the metabolism of dicarboxylic acids, which requires their oxidation to both oxaloacetate and pyruvate. In alfalfa bacteroids, production of pyruvate requires NAD + malic enzyme (Dme) but not NADP + malic enzyme (Tme). However, we show that Rhizobium leguminosarum has two pathways for pyruvate formation from dicarboxylates catalyzed by Dme and by the combined activities of phosphoenolpyruvate (PEP) carboxykinase (PckA) and pyruvate kinase (PykA). Both pathways enable N 2 fixation, but the PckA/PykA pathway supports N 2 fixation at only 60% of that for Dme. Double mutants of dme and pckA ykA did not fix N 2 . Furthermore, dme pykA double mutants did not grow on dicarboxylates, showing that they are the only pathways for the production of pyruvate from dicarboxylates normally expressed. PckA is not expressed in alfalfa bacteroids, resulting in an obligate requirement for Dme for pyruvate formation and N 2 fixation. When PckA was expressed from a constitutive nptII promoter in alfalfa dme bacteroids, acetylene was reduced at 30% of the wild-type rate, although this level was insufficient to prevent nitrogen starvation. Dme has N-terminal, malic enzyme (Me), and C-terminal phosphotransacetylase (Pta) domains. Deleting the Pta domain increased the peak acetylene reduction rate in 4-week-old pea plants to 140 to 150% of the wild-type rate, and this was accompanied by increased nodule mass. Plants infected with Pta deletion mutants did not have increased dry weight, demonstrating that there is not a sustained change in nitrogen fixation throughout growth. This indicates a complex relationship between pyruvate synthesis in bacteroids, nitrogen fixation, and plant growth.
Publisher: Elsevier
Date: 2012
Publisher: Scientific Societies
Date: 10-2019
Publisher: American Society for Microbiology
Date: 30-06-2016
Abstract: We report the complete genome sequence of Mesorhizobium ciceri strain CC1192, an efficient nitrogen-fixing microsymbiont of Cicer arietinum (chickpea). The genome consists of 6.94 Mb distributed between a single chromosome (6.29 Mb) and a plasmid (0.65 Mb).
Publisher: American Society for Microbiology
Date: 30-06-2016
Abstract: We report the complete genome sequence of Mesorhizobium ciceri bv. biserrulae strain WSM1284, a nitrogen-fixing microsymbiont of the pasture legume Biserrula pelecinus . The genome consists of 6.88 Mb distributed between a single chromosome (6.33 Mb) and a single plasmid (0.55 Mb).
Publisher: Microbiology Society
Date: 04-10-2021
Abstract: Members of the Mesorhizobium genus are soil bacteria that often form nitrogen-fixing symbioses with legumes. Most characterised Mesorhizobium spp. genomes are ~8 Mb in size and harbour extensive pangenomes including large integrative and conjugative elements (ICEs) carrying genes required for symbiosis (ICESyms). Here, we document and compare the conjugative mobilome of 41 complete Mesorhizobium genomes. We delineated 56 ICEs and 24 integrative and mobilizable elements (IMEs) collectively occupying 16 distinct integration sites, along with 24 plasmids. We also demonstrated horizontal transfer of the largest (853,775 bp) documented ICE, the tripartite ICE M spSym AA22 . The conjugation systems of all identified ICEs and several plasmids were related to those of the paradigm ICESym ICE Ml Sym R7A , with each carrying conserved genes for conjugative pilus formation ( trb ), excision ( rdfS ), DNA transfer ( rlxS ) and regulation ( fseA ). ICESyms have likely evolved from a common ancestor, despite occupying a variety of distinct integration sites and specifying symbiosis with erse legumes. We found extensive evidence for recombination between ICEs and particularly ICESyms, which all uniquely lack the conjugation entry-exclusion factor gene trbK . Frequent duplication, replacement and pseudogenization of genes for quorum-sensing-mediated activation and antiactivation of ICE transfer suggests ICE transfer regulation is constantly evolving. Pangenome-wide association analysis of the ICE identified genes potentially involved in symbiosis, rhizosphere colonisation and/or adaptation to distinct legume hosts. In summary, the Mesorhizobium genus has accumulated a large and dynamic pangenome that evolves through ongoing horizontal gene transfer of large conjugative elements related to ICE Ml Sym R7A .
Publisher: Public Library of Science (PLoS)
Date: 22-03-2018
Publisher: Springer Netherlands
Date: 2008
Publisher: BMJ
Date: 06-2006
Publisher: Elsevier BV
Date: 07-2017
DOI: 10.1016/J.PLASMID.2017.06.001
Abstract: Integrative and conjugative elements (ICEs) are generally regarded as regions of contiguous DNA integrated within a bacterial genome that are capable of excision and horizontal transfer via conjugation. We recently characterized a unique group of ICEs present in Mesorhizobium spp., which exist as three entirely separate but inextricably linked chromosomal regions termed α, β and γ. These regions occupy three different recombinase attachment (att) sites however, they do not excise independently. Rather, they recombine the host chromosome to form a single contiguous region prior to excision and conjugative transfer. Like the single-part ICE carried by M. loti R7A (ICEMlSym
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Jason Terpolilli.