A high-conductance cation channel from the inner membrane of the free-living soil bacteria Rhizobium etli

Rhizobium spp. are found in soil. They are both free-living and found symbiotically associated with the nodules of leguminous plants. Traditionally, studies have focused on the association of these organisms with plants in nitrogen-fixing nodules, since this is regarded as the most important role of these bacteria in the environment. Rhizobium sp. are known to possess several replicons. Some, like the Rhizobium etli symbiotic plasmid p42d and the plasmid pNGR234b of Rhizobium NGR234, have been sequenced and characterized. The plasmids from these organisms are the focus of this short review.

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First report of developmental changes inside the eggs of the Chinese freshwater crab, Sinopotamon yangtsekiense Bott, 1967 (Potamoidea, Potamidae), with comments on its evolutionary significance

Contributions to Zoology ◽

10.1163/18759866-07902003 ◽

2010 ◽

Vol 79 (2) ◽

pp. 79-84 ◽

Cited By ~ 6

Author(s):

Junzeng Xue ◽

Yan Liu ◽

Neil Cumberlidge ◽

Huixian Wu

Keyword(s):

Outer Membrane ◽

Morphological Changes ◽

Zhejiang Province ◽

Developmental Changes ◽

Evolutionary Significance ◽

Freshwater Crab ◽

Yolk Mass ◽

Free Living ◽

Inner Membrane ◽

Larval Stages

This paper focuses on the developmental changes that take place inside the eggs of the semi-terrestrial freshwater crab, Sinopotamon yangtsekiense, from Qiantang River in Zhejiang Province, China. The egg consists of two layers, a thick outer membrane and a thin inner membrane that encloses the fluidfilled embryonic sac. Development in this species took up to 77 days, after which the free-living juvenile hatchling crab emerged from the egg. During development the embryo underwent a series of morphological changes that corresponded to the free-living larval stages of marine crabs, and the yolk mass decreased in size and changed color (from creamy pale yellow, to orange, and finally grey). The eggs remained attached to the pleopods in the female’s abdominal brood pouch during development and showed a great deal of independence from water. Embryos developed normally whether they were immersed in water or in air. The implications of this adaptation for freshwater crab evolution are discussed.

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Differential Regulation of fixN-Reiterated Genes in Rhizobium etli by a Novel fixL—fixK Cascade

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi.2000.13.12.1283 ◽

2000 ◽

Vol 13 (12) ◽

pp. 1283-1292 ◽

Cited By ~ 50

Author(s):

Lourdes Girard ◽

Susana Brom ◽

Araceli Dávalos ◽

Oswaldo López ◽

Mario Soberón ◽

...

Keyword(s):

Nitrogen Fixation ◽

Regulatory Element ◽

Regulatory Gene ◽

Regulatory System ◽

Differential Regulation ◽

Rhizobium Etli ◽

Free Living ◽

Symbiotic Plasmid ◽

Independent Mechanism ◽

Fusion Analysis

Among the complexities in the regulation of nitrogen fixation in the Rhizobiaceae are reiteration of regulatory components as well as variant roles for each component between species. For Rhizobium etli CFN42, we reported that the symbiotic plasmid (pCFN42d) contains a key regulatory gene (fixKd) and genes for a symbiotic cytochrome oxidase (fixNOQPd). Here we discuss the occurrence of reiteration of these genes (fixKf and fixNOQPf) and the finding of an unusual fixL homolog on a plasmid previously considered cryptic (pCFN42f). The structure of the deduced FixL polypeptide is suggestive of a fusion of the receiver and transmitter modules of a two-component regulatory system as described in R. leguminosarum bv. viciae VF39. Gene fusion analysis, coupled with mutation of each regulatory element, revealed that free-living expression of FixKf was dependent fully on FixL. In contrast, synthesis of FixKd was not detected under the conditions tested. The FixKf protein is needed for microaerobic expression of both fixN reiterations, whereas the FixKd protein appears to be dispensable. Interestingly, expression of the fixN reiterations exhibits a differential dependence for FixL, where transcription of fixNf was suppressed in the absence of FixL but expression of fixNd still showed significant levels. This suggests the existence of a FixL-independent mechanism for expression of the fixNd reiteration. Surprisingly, mutations in fixL, fixKd, or fixKf (either singly or in combination) did not alter symbiotic effectiveness. A mutation in fixNd (but not in fixNf) was, however, severely affected, indicating a differential role for these reiterations in nitrogen fixation.

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Further investigation on the high-conductance ion channel of the inner membrane of mitochondria

Journal of Bioenergetics and Biomembranes ◽

10.1007/bf00762520 ◽

1989 ◽

Vol 21 (4) ◽

pp. 485-496 ◽

Cited By ~ 46

Author(s):

M. Catia Sorgato ◽

Oscar Moran ◽

Vito De Pinto ◽

Bernhard U. Keller ◽

Walter Stuehmer

Keyword(s):

Ion Channel ◽

Inner Membrane ◽

High Conductance

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From Intracellular Bacteria to Differentiated Bacteroids: Transcriptome and Metabolome Analysis inAeschynomeneNodules Using theBradyrhizobiumsp. Strain ORS285bclAMutant

Journal of Bacteriology ◽

10.1128/jb.00191-19 ◽

2019 ◽

Vol 201 (17) ◽

Author(s):

Florian Lamouche ◽

Anaïs Chaumeret ◽

Ibtissem Guefrachi ◽

Quentin Barrière ◽

Olivier Pierre ◽

...

Keyword(s):

Gene Expression ◽

Transcriptome Analysis ◽

Soil Bacteria ◽

Regulation Of Gene Expression ◽

Nitrogen Fertilizers ◽

Peptide Transporter ◽

Intracellular Bacteria ◽

Nitrogen Fixing ◽

Wild Type ◽

Free Living

ABSTRACTSoil bacteria called rhizobia trigger the formation of root nodules on legume plants. The rhizobia infect these symbiotic organs and adopt an intracellular lifestyle within the nodule cells, where they differentiate into nitrogen-fixing bacteroids. Several legume lineages force their symbionts into an extreme cellular differentiation, comprising cell enlargement and genome endoreduplication. The antimicrobial peptide transporter BclA is a major determinant of this process inBradyrhizobiumsp. strain ORS285, a symbiont ofAeschynomenespp. In the absence of BclA, the bacteria proceed until the intracellular infection of nodule cells, but they cannot differentiate into enlarged polyploid and functional bacteroids. Thus, thebclAnodule bacteria constitute an intermediate stage between the free-living soil bacteria and the nitrogen-fixing bacteroids. Metabolomics on whole nodules ofAeschynomene afrasperaandAeschynomene indicainfected with the wild type or thebclAmutant revealed 47 metabolites that differentially accumulated concomitantly with bacteroid differentiation. Bacterial transcriptome analysis of these nodules demonstrated that the intracellular settling of the rhizobia in the symbiotic nodule cells is accompanied by a first transcriptome switch involving several hundred upregulated and downregulated genes and a second switch accompanying the bacteroid differentiation, involving fewer genes but ones that are expressed to extremely elevated levels. The transcriptomes further suggested a dynamic role for oxygen and redox regulation of gene expression during nodule formation and a nonsymbiotic function of BclA. Together, our data uncover the metabolic and gene expression changes that accompany the transition from intracellular bacteria into differentiated nitrogen-fixing bacteroids.IMPORTANCELegume-rhizobium symbiosis is a major ecological process, fueling the biogeochemical nitrogen cycle with reduced nitrogen. It also represents a promising strategy to reduce the use of chemical nitrogen fertilizers in agriculture, thereby improving its sustainability. This interaction leads to the intracellular accommodation of rhizobia within plant cells of symbiotic organs, where they differentiate into nitrogen-fixing bacteroids. In specific legume clades, this differentiation process requires the bacterial transporter BclA to counteract antimicrobial peptides produced by the host. Transcriptome analysis ofBradyrhizobiumwild-type andbclAmutant bacteria in culture and in symbiosis withAeschynomenehost plants dissected the bacterial transcriptional response in distinct phases and highlighted functions of the transporter in the free-living stage of the bacterial life cycle.

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Rhizobium etli Genetically Engineered for the Heterologous Expression of Vitreoscilla sp. Hemoglobin: Effects on Free-Living and Symbiosis

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi.1999.12.11.1008 ◽

1999 ◽

Vol 12 (11) ◽

pp. 1008-1015 ◽

Cited By ~ 37

Author(s):

Mario Ramírez ◽

Brenda Valderrama ◽

Raúl Arredondo-Peter ◽

Mario Soberón ◽

Jaime Mora ◽

...

Keyword(s):

Nitrogen Fixation ◽

Heterologous Expression ◽

Energy Content ◽

Nitrogenase Activity ◽

Polyacrylamide Gel Electrophoresis ◽

Sodium Dodecyl ◽

Rhizobium Etli ◽

Free Living ◽

Cell Extracts ◽

Bean Plants

Oxygen concentration is an environmental signal that regulates nitrogen fixation in the Rhizobium-legume symbiosis. We investigated the effect of the heterologous expression of Vitreoscilla sp. hemoglobin (VHb), which is an oxygen-binding protein, in Rhizobium etli. The vhb gene and its native promoter were subcloned in the plasmid pMR4 and transformed into the R. etli strain CE3. Free-living cultures of engineered R. etli CE3 expressed the vhb gene, as shown by the CO-difference spectral and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analyses of cell extracts. The expression of vhb in free-living R. etli grown under most limiting oxygen concentrations resulted in an increase in respiratory activity, chemical energy content, and expression of the nitrogen-fixation gene nifHc. Bacteroids isolated from nodules of bean plants inoculated with the engineered R. etli CE3 expressed the vhb gene, as shown by RNA slot-blot analysis. Bean plants inoculated with the engineered strain exhibited higher nitrogenase activity and total nitrogen content (68% and 14 to 53%, respectively) than bean plants inoculated with the R. etli wild type. These results suggest that the synthesis of VHb in engineered R. etli stimulated the respiratory efficiency of free-living rhizobia, and also probably of symbiotic bacteroids, thus leading to higher levels of symbiotic nitrogen fixation.

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