1
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Steidinger BS, Bever JD. Host discrimination in modular mutualisms: a theoretical framework for meta-populations of mutualists and exploiters. Proc Biol Sci 2016; 283:rspb.2015.2428. [PMID: 26740613 DOI: 10.1098/rspb.2015.2428] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Plants in multiple symbioses are exploited by symbionts that consume their resources without providing services. Discriminating hosts are thought to stabilize mutualism by preferentially allocating resources into anatomical structures (modules) where services are generated, with examples of modules including the entire inflorescences of figs and the root nodules of legumes. Modules are often colonized by multiple symbiotic partners, such that exploiters that co-occur with mutualists within mixed modules can share rewards generated by their mutualist competitors. We developed a meta-population model to answer how the population dynamics of mutualists and exploiters change when they interact with hosts with different module occupancies (number of colonists per module) and functionally different patterns of allocation into mixed modules. We find that as module occupancy increases, hosts must increase the magnitude of preferentially allocated resources in order to sustain comparable populations of mutualists. Further, we find that mixed colonization can result in the coexistence of mutualist and exploiter partners, but only when preferential allocation follows a saturating function of the number of mutualists in a module. Finally, using published data from the fig-wasp mutualism as an illustrative example, we derive model predictions that approximate the proportion of exploiter, non-pollinating wasps observed in the field.
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Affiliation(s)
- Brian S Steidinger
- Ecology, Evolution, and Behavior, Indiana University, Bloomington, IN, USA
| | - James D Bever
- Ecology, Evolution, and Behavior, Indiana University, Bloomington, IN, USA
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2
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Evolutionary dynamics of nitrogen fixation in the legume-rhizobia symbiosis. PLoS One 2014; 9:e93670. [PMID: 24691447 PMCID: PMC3972148 DOI: 10.1371/journal.pone.0093670] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2013] [Accepted: 03/09/2014] [Indexed: 11/19/2022] Open
Abstract
The stabilization of host–symbiont mutualism against the emergence of parasitic individuals is pivotal to the evolution of cooperation. One of the most famous symbioses occurs between legumes and their colonizing rhizobia, in which rhizobia extract nutrients (or benefits) from legume plants while supplying them with nitrogen resources produced by nitrogen fixation (or costs). Natural environments, however, are widely populated by ineffective rhizobia that extract benefits without paying costs and thus proliferate more efficiently than nitrogen-fixing cooperators. How and why this mutualism becomes stabilized and evolutionarily persists has been extensively discussed. To better understand the evolutionary dynamics of this symbiosis system, we construct a simple model based on the continuous snowdrift game with multiple interacting players. We investigate the model using adaptive dynamics and numerical simulations. We find that symbiotic evolution depends on the cost–benefit balance, and that cheaters widely emerge when the cost and benefit are similar in strength. In this scenario, the persistence of the symbiotic system is compatible with the presence of cheaters. This result suggests that the symbiotic relationship is robust to the emergence of cheaters, and may explain the prevalence of cheating rhizobia in nature. In addition, various stabilizing mechanisms, such as partner fidelity feedback, partner choice, and host sanction, can reinforce the symbiotic relationship by affecting the fitness of symbionts in various ways. This result suggests that the symbiotic relationship is cooperatively stabilized by various mechanisms. In addition, mixed nodule populations are thought to encourage cheater emergence, but our model predicts that, in certain situations, cheaters can disappear from such populations. These findings provide a theoretical basis of the evolutionary dynamics of legume–rhizobia symbioses, which is extendable to other single-host, multiple-colonizer systems.
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3
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Simonsen AK, Stinchcombe JR. Herbivory eliminates fitness costs of mutualism exploiters. THE NEW PHYTOLOGIST 2014; 202:651-661. [PMID: 24428169 DOI: 10.1111/nph.12668] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2013] [Accepted: 11/28/2013] [Indexed: 05/07/2023]
Abstract
A common empirical observation in mutualistic interactions is the persistence of variation in partner quality and, in particular, the persistence of exploitative phenotypes. For mutualisms between hosts and symbionts, most mutualism theory assumes that exploiters always impose fitness costs on their host. We exposed legume hosts to mutualistic (nitrogen-fixing) and exploitative (non-nitrogen-fixing) symbiotic rhizobia in field conditions, and manipulated the presence or absence of insect herbivory to determine if the costly fitness effects of exploitative rhizobia are context-dependent. Exploitative rhizobia predictably reduced host fitness when herbivores were excluded. However, insects caused greater damage on hosts associating with mutualistic rhizobia, as a consequence of feeding preferences related to leaf nitrogen content, resulting in the elimination of fitness costs imposed on hosts by exploitative rhizobia. Our experiment shows that herbivory is potentially an important factor in influencing the evolutionary dynamic between legumes and rhizobia. Partner choice and host sanctioning are theoretically predicted to stabilize mutualisms by reducing the frequency of exploitative symbionts. We argue that herbivore pressure may actually weaken selection on choice and sanction mechanisms, thus providing one explanation of why host-based discrimination mechanisms may not be completely effective in eliminating nonbeneficial partners.
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Affiliation(s)
- Anna K Simonsen
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada
| | - John R Stinchcombe
- Department of Ecology and Evolutionary Biology, Centre for the Analysis of Genome Evolution and Function, University of Toronto, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada
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4
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Triplett EW. Construction of a Symbiotically Effective Strain of Rhizobium leguminosarum bv. trifolii with Increased Nodulation Competitiveness. Appl Environ Microbiol 2010; 56:98-103. [PMID: 16348109 PMCID: PMC183256 DOI: 10.1128/aem.56.1.98-103.1990] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Genes involved in nodulation competitiveness (tfx) were inserted by marker exchange into the genome of the effective strain Rhizobium leguminosarum bv. trifolii TA1. Isogenic strains of TA1 were constructed which differed only in their ability to produce trifolitoxin, an antirhizobial peptide. Trifolitoxin production by the ineffective strain R. leguminosarum bv. trifolii T24 limited nodulation of clover roots by trifolitoxin-sensitive strains of R. leguminosarum bv. trifolii. The trifolitoxin-producing exconjugant TA1::10-15 was very competitive for nodulation on clover roots when coinoculated with a trifolitoxin-sensitive reference strain. The nonproducing exconjugant TA1::12-10 was not competitive for nodule occupancy when coinoculated with the reference strain. Tetracycline sensitivity and Southern analysis confirmed the loss of vector DNA in the exconjugants. Trifolitoxin production by TA1::10-15 was stable in the absence of selection pressure. Transfer of tfx to TA1 did not affect nodule number or nitrogenase activity. These experiments represent the first stable genetic transfer of genes involved in nodulation competitiveness to a symbiotically effective Rhizobium strain.
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Affiliation(s)
- E W Triplett
- Department of Agronomy and Center for the Study of Nitrogen Fixation, 1575 Linden Drive, University of Wisconsin-Madison, Madison, Wisconsin 53706
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5
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McDermoti TR, Graham PH. Competitive Ability and Efficiency in Nodule Formation of Strains of Bradyrhizobium japonicum. Appl Environ Microbiol 2010; 56:3035-9. [PMID: 16348311 PMCID: PMC184895 DOI: 10.1128/aem.56.10.3035-3039.1990] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In the American Midwest, superior N(2)-fixing inoculant strains of Bradyrhizobium japonicum consistently fail to produce the majority of nodules on the roots of field-grown soybean. Poor nodulation by inoculant strains is partly due to their inability to stay abreast of the expanding soybean root system in numbers sufficient for them to be competitive with indigenous bradyrhizobia. However, certain strains are noncompetitive even when numerical dominance is not a factor. In this study, we tested the hypothesis that the nodule occupancy achieved by strains is related to their nodule-forming efficiency. The nodulation characteristics and competitiveness of nine strains of B. japonicum were compared at both 20 and 30 degrees C. The root tip marking technique was used, with the nodule-forming efficiency of each strain estimated from the average position of the uppermost nodule and the number of nodules formed above the root tip mark. The competitiveness of the nine strains relative to B. japonicum USDA 110 was determined by using immunofluorescence to identify nodule occupants. The strains differed significantly in competitiveness with USDA 110 and in nodulation characteristics, strains that were poor competitors usually proving to be inferior in both the average position of the uppermost root nodule and the number of nodules formed above the root tip mark. Thus, competitiveness was correlated with both the average position of the uppermost nodule (r = 0.5; P = 0.036) and the number of nodules formed above the root tip mark (r = 0.64; P = 0.005), while the position of the uppermost nodule was also correlated to the percentage of plants nodulated above the root tip mark (r = 0.81; P < 0.001) and the percentage of plants nodulated on the taproot (r = 0.67; P = 0.002).
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Affiliation(s)
- T R McDermoti
- Rhizobium Research Laboratory, Department of Soil Science, University of Minnesota, St. Paul, Minnesota 55108
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6
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Leung K, Wanjage FN, Bottomley PJ. Symbiotic Characteristics of Rhizobium leguminosarum bv. trifolii Isolates Which Represent Major and Minor Nodule-Occupying Chromosomal Types of Field-Grown Subclover (Trifolium subterraneum L.). Appl Environ Microbiol 2010; 60:427-33. [PMID: 16349172 PMCID: PMC201330 DOI: 10.1128/aem.60.2.427-433.1994] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The symbiotic effectiveness and nodulation competitiveness of Rhizobium leguminosarum bv. trifolii soil isolates were evaluated under nonsoil greenhouse conditions. The isolates which we used represented both major and minor nodule-occupying chromosomal types (electrophoretic types [ETs]) recovered from field-grown subclover (Trifolium subterraneum L.). Isolates representing four ETs (ETs 2, 3, 7, and 8) that were highly successful field nodule occupants fixed between 2- and 10-fold less nitrogen and produced lower herbage dry weights and first-harvest herbage protein concentrations than isolates that were minor nodule occupants of field-grown plants. Despite their equivalent levels of abundance in nodules on field-grown subclover plants, ET 2 and 3 isolates exhibited different competitive nodulation potentials under nonsoil greenhouse conditions. ET 3 isolates generally occupied more subclover nodules than isolates belonging to other ETs when the isolates were mixed in 1:1 inoculant ratios and inoculated onto seedlings. In contrast, ET 2 isolates were less successful at nodulating under these conditions. In many cases, ET 2 isolates required a numerical advantage of at least 6:1 to 11:1 to occupy significantly more nodules than their competitors. We identified highly effective isolates that were as competitive as the ET 3 isolates despite representing serotypes that were rarely recovered from nodules of field-grown plants. When one of the suboptimally effective isolates (ET2-1) competed with an effective and competitive isolate (ET31-5) at several different inoculant ratios, the percentages of nodules occupied by the former increased as its numerical advantage increased. Although subclover yields declined as nodule occupancy by ET2-1 increased, surprisingly, this occurred at inoculant ratios at which large percentages of nodules were still occupied by ET31-5.
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Affiliation(s)
- K Leung
- Department of Microbiology, Oregon State University, Corvallis, Oregon 97331-3804
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7
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Leung K, Yap K, Dashti N, Bottomley PJ. Serological and Ecological Characteristics of a Nodule-Dominant Serotype from an Indigenous Soil Population of Rhizobium leguminosarum bv. trifolii. Appl Environ Microbiol 2010; 60:408-15. [PMID: 16349170 PMCID: PMC201328 DOI: 10.1128/aem.60.2.408-415.1994] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Although at least 13 antigenically distinct serotypes of Rhizobium leguminosarum bv. trifolii exist in an Abiqua silty clay loam soil, one serotype, AS6, occupies >/=50% of the root nodules formed on field-grown subclover and between 33 and 78% of the nodules formed on five annual clover species grown in the same soil under laboratory conditions. The dominance of subclover nodules by serotype AS6 was reproducible over a 4-year sampling period and throughout the entire 200- by 100-m pasture examined. Serotype AS6 was composed of three antigenically distinct subtypes (AS6-a, AS6-b, and AS6-c). Each subtype contributed about one-third of the AS6 isolates recovered from nodules of field-grown subclover plants and maintained similar population densities in nonrhizosphere and rhizosphere soil. Rhizobia with the AS6 antigenic signature accounted for from 20 to 100% of the soil populations of R. leguminosarum in arable and pasture soils under legumes throughout the state of Oregon. Over a 12-month period, the population densities of the serotype AS6 complex and three minor nodule-occupying serotypes (AG4, AP17, and AS21) were measured in the rhizospheres of field-grown subclover and orchard grass and in nonrhizosphere Abiqua soil. Regardless of season or serotype, the orchard grass rhizosphere effect was minimal, with the ratio between rhizosphere and nonrhizosphere serotype population densities ranging between 2.5 (midsummer) and 10.5 (spring). In contrast, the magnitude of the subclover rhizosphere effect varied seasonally and among serotypes. Between October and December the ratios for all serotypes were similar (12.5 to 25.5). However, in the spring (April and May), the magnitude of the rhizosphere effect varied among the indigenous serotypes (ratios, 10.5 to 442) and for minor nodule-occupying serotypes AS21 (ratio, 442) and AP17 (ratio, 47) was as great as, or even greater than, the magnitude of the rhizosphere effect observed with the AS6 complex (ratio, 65.5).
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Affiliation(s)
- K Leung
- Department of Microbiology, Oregon State University, Corvallis, Oregon 97331-3804
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8
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Kiers ET, Denison RF. Sanctions, Cooperation, and the Stability of Plant-Rhizosphere Mutualisms. ANNUAL REVIEW OF ECOLOGY EVOLUTION AND SYSTEMATICS 2008. [DOI: 10.1146/annurev.ecolsys.39.110707.173423] [Citation(s) in RCA: 234] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- E. Toby Kiers
- Faculteit der Aard – en Levenswetenschappen, De Boelelaan 1085, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands;
| | - R. Ford Denison
- Department of Ecology, Evolution, & Behavior, University of Minnesota, St. Paul, Minnesota 55108;
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9
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Kiers ET, West SA, Denison RF. Mediating mutualisms: farm management practices and evolutionary changes in symbiont co-operation. J Appl Ecol 2002. [DOI: 10.1046/j.1365-2664.2002.00755.x] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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10
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Denison RF. Legume Sanctions and the Evolution of Symbiotic Cooperation by Rhizobia. Am Nat 2000; 156:567-576. [DOI: 10.1086/316994] [Citation(s) in RCA: 249] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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11
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Nick G, Lindström K. Use of Repetitive Sequences and the Polymerase Chain Reaction to Fingerprint the Genomic DNA of Rhizobium galegae Strains and to Identify the DNA Obtained by Sonicating the Liquid Cultures and Root Nodules. Syst Appl Microbiol 1994. [DOI: 10.1016/s0723-2020(11)80018-4] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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12
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Lindström K, Lipsanen P, Kaijalainen S. Stability of Markers Used for Identification of Two
Rhizobium galegae
Inoculant Strains after Five Years in the Field. Appl Environ Microbiol 1990; 56:444-50. [PMID: 16348119 PMCID: PMC183359 DOI: 10.1128/aem.56.2.444-450.1990] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The stability of identification markers was examined for two
Rhizobium galegae
inoculant strains after 5 years in the field. The two strains are genetically closely related, but differ in their lipopolysaccharides. Strain HAMBI 540 has lipopolysaccharide of the rough type, whereas that of strain HAMBI 1461 is of the smooth type. The properties that were examined for 10 field isolates of each inoculant type were symbiotic phenotype, phage type, intrinsic antibiotic resistance, maximum growth temperature, lipopolysaccharide and total soluble protein patterns, immunological properties, DNA restriction profiles, and DNA hybridization patterns, which were determined by using
nifHDK
and
recA
sequences as probes. Of these properties, all remained stable in soil, with the exception of some variation in intrinsic antibiotic resistance and the acquisition of an extra
Eco
RI restriction fragment by one of the isolates. Thus, both the rough and the smooth lipopolysaccharide phenotypes persisted equally well in soil.
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Affiliation(s)
- K Lindström
- Department of Microbiology, University of Helsinki, SF-00710 Helsinki, Finland
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13
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Trinick MJ, Goodchild DJ, Miller C. Localization of Bacteria and Hemoglobin in Root Nodules of
Parasponia andersonii
Containing Both
Bradyrhizobium
Strains and
Rhizobium leguminosarum
biovar
trifolii. Appl Environ Microbiol 1989; 55:2046-2055. [PMID: 16347995 PMCID: PMC203001 DOI: 10.1128/aem.55.8.2046-2055.1989] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Dual occupancy of
Parasponia andersonii
nodules with different
Bradyrhizobium
strains and
Rhizobium leguminosarum
biovar
trifolii
was frequently obtained when two strains were inoculated into plants grown aseptically in tubes. Since reisolates of
Bradyrhizobium
strains from dually occupied nodules acquired the ability to nodulate
Trifolium repens
, the spatial relationship of the two species of bacteria during nodule initiation and development was investigated and their proximity was demonstrated. By using light microscopy and electron microscopy and immunogold labeling,
R. leguminosarum
biovar
trifolii
NGR66 inoculated alone onto
P. andersonii
produced small ineffective nodules, with bacteria embedded in matrix material in intercellular spaces and in a few nonliving host cells rather than in infection threads (CP299). In dual infections, the two bacterial species were shown to be adjacent to one another in the matrix of nodule intercellular spaces and in some host nodule cells. However, when two different
Bradyrhizobium
strains occupied a single nodule, they were located in different lobes of the same nodule. Immunogold labeling showed that
Parasponia
hemoglobin was localized in the cytoplasm of young infected nodule cells. This suggests that the nitrogen-fixing phase of
Parasponia
nodule cells is short-lived and correlates with previous acetylene reduction data from nodule slices. Hemoglobin was associated only with areas of nodule tissue infected with the effective nitrogen-fixing strain CP299 and absent from areas infected with
R. leguminosarum
biovar
trifolii
.
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Affiliation(s)
- Michael J Trinick
- Division of Plant Industry, Commonwealth Scientific and Industrial Research Organization, GPO Box 1600, Canberra City, 2601, Australia
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14
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Trinick MJ, Hadobas PA. Competition by
Bradyrhizobium
Strains for Nodulation of the Nonlegume
Parasponia andersonii. Appl Environ Microbiol 1989; 55:1242-8. [PMID: 16347913 PMCID: PMC184284 DOI: 10.1128/aem.55.5.1242-1248.1989] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Bradyrhizobium
strains isolated from the nonlegume
Parasponia
spp. formed a group of strains that were highly competitive for nodulation of
P. andersonii
when paired with strains isolated from legumes. Strains from legumes, including those of similar effectiveness to NGR231 and CP283, were not able to form nodules as single occupants on
P. andersonii
in the presence of
Parasponia
strains. However, NGR86, an isolate from
Macroptilium lathyroides
, jointly occupied one-third of the nodules formed with each of the three strains isolated from
Parasponia
spp. Time taken for nodules to appear may have influenced the outcome of competition, since CP283 and all isolates from legumes were slow to nodulate
P. andersonii
. Among the
Parasponia
strains, competitiveness for nodulation of
P. andersonii
was not associated with effectiveness of nitrogen fixation. The highly effective strain CP299 was a poor competitor when paired with the least effective strain NGR231. CP283 was the least competitive of the
Parasponia
strains but was still able to dominate nodules when paired with legume isolates. Dual occupancy was high, up to 67% when the inoculum contained CP299 and CP273. Both the Muc
+
and Muc
-
types of CP283 form a symbiosis of similar effectiveness and were similarly competitive at high inoculation densities, but the Muc
-
form was more competitive at low inoculum densities. Both forms frequently occupied the same nodule.
Bradyrhizobium
strains isolated from
Parasponia
spp. may have specific genetic information that favor their ability to competitively and effectively infect plants in the genus
Parasponia
(Ulmaceae) outside the Leguminosae.
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Affiliation(s)
- M J Trinick
- Division of Plant Industry, Commonwealth Scientific and Industrial Research Organisation, G.P.O. Box 1600, Canberra City Australian Capital Territory 2601, Australia
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15
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Leung K, Bottomley PJ. Influence of Phosphate on the Growth and Nodulation Characteristics of
Rhizobium trifolii. Appl Environ Microbiol 1987; 53:2098-105. [PMID: 16347432 PMCID: PMC204064 DOI: 10.1128/aem.53.9.2098-2105.1987] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The growth and nodulating characteristics of
Rhizobium trifolii
6 and 36 differed under different external phosphate conditions. Under growth conditions designed to deplete the internal phosphate content of the rhizobia, strain 6 maintained a generation time of 5 h during the exponential phase over two cycles of growth in phosphate-depleted medium. In contrast, the generation time of strain 36 was extended from 3.5 to 9.8 h over two cycles of phosphate-depleted growth, although the organism eventually achieved the same cell density and cellular phosphate content as that of strain 6 at stationary phase. Phosphate-depleted strain 6 required 0.51 ± 0.08 μM phosphate to commence proliferation, whereas phosphate-depleted strain 36 required 0.89 ± 0.04 μM phosphate under the same conditions. Phosphate-depleted strain 6 maintained viability when exposed to external phosphate concentrations subcritical for growth to occur, whereas phosphate-depleted strain 36 lost viability within 48 h when exposed to medium containing phosphate at concentrations subcritical for growth. Phosphate-depleted strain 36 was inferior to phosphate-depleted strain 6 at nodulating subterranean clover (
Trifolium subterraneum
L. cv. Mt. Barker) by taking 2 to 4 days longer to develop nodules in phosphatedepleted plant grown medium at pH 5.5. Nodulation by phosphate-depleted strain 36 was accelerated either by including phosphate in the plant growth medium at pH 5.5 or by raising the solution pH of phosphate-depleted plant growth medium to pH 6.5. External phosphate and pH effects were not observed on the nodulating capabilities of phosphate-depleted strain 6 or on luxury phosphate-grown cells of either strain. Phosphatedepleted strains 6 and 36 proliferated to a similar extent on the rhizoplanes even under stringently low external P
i
concentrations. The phosphatase activities of both phosphate-depleted strains were significantly (
P
= 0.05) higher at pH 6.5 than at pH 5.5, and the activity of strain 6 was significantly higher (
P
= 0.05) than that of strain 36 at pH 5.5 and 5.0.
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Affiliation(s)
- K Leung
- Departments of Soil Science and Microbiology, Oregon State University, Corvallis, Oregon 97331-3804
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16
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Demezas DH, Bottomley PJ. Influence of Soil and Nonsoil Environments on Nodulation by
Rhizobium trifolii. Appl Environ Microbiol 1987; 53:596-7. [PMID: 16347307 PMCID: PMC203713 DOI: 10.1128/aem.53.3.596-597.1987] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Indigenous serotypes 1-01 and 2-02 of
Rhizobium trifolii
occupied similar percentages (18 to 23%) of root nodules on soil-grown subclover (
Trifolium subterraneum
L.) and were virtually absent (4.5%) from nodules of soil-grown white clover (
Trifolium repens
L.). In contrast (with the exception of one dilution [10
−4
]), serotype 1-01 occupied a substantial portion of nodules (16 to 40%) on white clover seedlings grown on mineral salts agar and exposed to samples of the same soil in the form of a 10-fold dilution series (10
−1
to 10
−5
). Under the latter conditions, occupancy of subclover nodules by 1-01 and of nodules of both plant species by 2-02 was consistent with the results obtained with soil-grown plants.
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Affiliation(s)
- D H Demezas
- Departments of Microbiology and Soil Science, Oregon State University, Corvallis, Oregon 97331-3804
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17
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Demezas DH, Bottomley PJ. Autecology in Rhizospheres and Nodulating Behavior of Indigenous
Rhizobium trifolii. Appl Environ Microbiol 1986; 52:1014-9. [PMID: 16347198 PMCID: PMC239166 DOI: 10.1128/aem.52.5.1014-1019.1986] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Indigenous serotype 1-01 of
Rhizobium trifolii
occupied significantly fewer nodules (6%) on plants of soil-grown noninoculated subterranean clover (
Trifolium subterraneum
L.) cv. Woogenellup than on cv. Mt. Barker (36%) sampled at the flowering stage of growth. Occupancy by indigenous serotype 2-01, was not significantly different on the two cultivars (16 and 26%). Serotype-specific, fluorescent-antibody conjugates were synthesized and used to enumerate the indigenous serotypes in host (clovers) and nonhost (annual rye-grass,
Lolium multiflorum
L.) rhizospheres and in nonplanted soil. The form and concentration of Ca
2+
in the flocculating mixture and the presence of phosphate anions in the extracting solution were both critical for enumerating
R. trifolii
in Whobrey soil. The two serotypes were present in similar numbers in nonplanted soil (ca. 10
6
per g of soil) and each represented ca. 10% of the total
R. trifolii
population. Although host rhizospheres did not preferentially stimulate either serotype, the mean population densities of serotype 2-01 were significantly greater (
P
= 0.05) than those of serotype 1-01 in clover rhizospheres on 8 of 14 samplings made between the time of seeding and the appearance of nodules (day 12). In this experiment, and in contrast to our earlier findings, serotype 1-01 occupied significantly fewer (
P
≤ 0.05) of the nodules (7 to 16%) on both cultivars than serotype 2-01 (51%) when sampled at 4 weeks. Differences between cultivars became apparent as the plants matured. There was a threefold increase (7 to 21%) in nodules occupied by serotype 1-01 on cv. Mt. Barker between 4 and 16 weeks. This was accompanied by increases in nodules coinhabited by both nonidentifiable occupants and either serotype 1-01 (0 to 20%) or 2-01 (11 to 51%). No increases in either of these parameters were observed on cv. Woogenellup.
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Affiliation(s)
- D H Demezas
- Departments of Microbiology and Soil Science, Oregon State University, Corvallis, Oregon 97331-3804
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