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1

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Conserved plasmid/chromosome sequences in fast- and slow-growing rhizobia that nodulate the same plant (1985)

Broughton, W. J. ; Bohlool, B. B. ; Shaw, C. H. ; [et al.]

Springer

Archives of microbiology 141 (1985), S. 14-21

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ISSN: 1432-072X

Keywords: NifKDH genes ; Nitrogenase ; Sym plasmid ; Nod genes

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Apart from the ability to nodulate legumes, fast-and slow-growing rhizobia have few bacteriological traits in common. Given that there is only one pathway to nodulation, DNA sequences conserved in fast- and slow-growing organisms that nodulate the same host should be strongly enriched in infectivity genes. We tested this hypothesis with seven fast-growing and five slow-growing strains that produced responses varying from fully effective nodulation through various ineffective associations to non-nodulation on four different hosts (Lotus pedunculatus, Lupinus nanus, Macroptilium atropurpureum, and Vigna unguiculata). When restriction enzyme digested total DNA from 10 of the strains was separately hybridized with nick-translated plasmid DNA isolated from 4 fast-growing strains, variable but significant homologies were found with all 10 strains. Part of this homology was shown to be associated with the nifKDH genes for nitrogenase and part with putative nodulation genes carried on pC2, a cosmid clone containing a 37 kbp region of the large sym plasmid present in the fast-growing broad-host range Rhizobium sp. strain NGR234. Analysis of the extent of homology between the plasmids of 3 fastgrowing strains (NGR234, TAL 996 and UMKL 19) able to effectively nodulate Vigna unguiculata showed them to have homologous DNA fragments totalling 47 kbp. This “core” homology represents less than 12% of the total coding capacity of the sym plasmid present in each of these strains.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00446733

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2

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Genetic variation among populations of Pythium irregulare in southern Australia (2000)

Harvey, P. R. ; Butterworth, P. J. ; Hawke, B. G. ; [et al.]

Oxford, UK : Blackwell Science Ltd

Plant pathology 49 (2000), S. 0

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ISSN: 1365-3059

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Isolates of Pythium irregulare were sampled from seven cereal crops throughout South Australia to determine the extent of genetic diversity within this pathogen and the scale of genetic differentiation among populations. Data derived from 29 individual restriction fragment length polymorphism (RFLP) loci differentiated 54 DNA fingerprints among the 92 isolates analysed. Some isolates had two alleles at several RFLP loci and were scored as heterozygous. One such isolate was selfed in vitro and segregation ratios in the progeny were not significantly different from those expected for allelic variation in a diploid. These data provided evidence that outcrossing occurs within P. irregulare and may contribute to the high level of genetic variation within the species (DT = 0·502). Allelic frequencies were significantly different among all seven populations and GST values showed significant genetic differentiation between populations. The average genetic identity among populations was low and hierarchical cluster analysis provided no clear evidence that populations formed geographically related groups. These analyses indicate low levels of interpopulation gene flow within P. irregulare and imply that population differentiation results from genetic drift.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-3059.2000.00493.x

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3

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The effect of bacterial strain and temperature changes on the nitrogenase activity of Lotus pedunculatus root nodules (1984)

Pankhurst, C. E. ; Layzell, D. B.

Oxford, UK : Blackwell Publishing Ltd

Physiologia plantarum 62 (1984), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: After 40 days of growth at 25°C, Lotus pedunculatus cav., cv. Maku plants infected with Rhizobium loti strain NZP2037 displayed similar relative growth rates but had twice the nodule mass and only one third the whole plant dry weight of plants infected with Bradyrhizobium sp. (Lotus) strain CC814s. In the NZP2037 symbiosis, the rate of CO2 evolution (per g dry weight of nodulated root) was 1.6 times as high as that in the CC814s symbiosis while the rate of C2H2 reduction (per g dry weight of nodule) was only 48% of that in the CC814s symbiosis. Studies of the effect of short term temperature changes on the gas exchange characteristics (CO2 and H2 evolution, C2H2 reduction) of these symbioses revealed wide differences in the optima for C2H2 reduction. Nodules infected with NZP2037 displayed maximal C2H2 reduction rates [157 μmol (g dry weight nodule)−1 h−1] at 12°C, whereas nodules infected with CC814s were optimal at 30°C [208 μmol (g dry weight nodule)−1 h−1]. These short term studies suggested that differences in temperature optima for N2 may have partially accounted for the poorer effectivity, at 25°C, of strain NZP2037 when compared with strain CC-814s.The relative efficiency [RE = 1 – (H2 evolution/C2H2 reduction)] of N2 fixation varied widely with temperature in the two symbioses, but there was a general trend toward higher RE with lower temperatures. The ratio of CO2 evolution: C2H2 reduction (mol/mol) in nodulated roots infected with CC814s was constant (ca 10 CO2/C2H2) between 5°C and 30°C, whereas in plants infected with NZP2037 it reached a minimal value of 3.3 CO2/C2H2 at 10°C and was 19 CO2/C2H2 at the growing temperature (25°C).

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1399-3054.1984.tb04593.x

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4

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Effect of plant nutrient supply on nodule effectiveness and rhizobium strain competition for nodulation ofLotus pedunculatus (1981)

Pankhurst, C. E.

Springer

Plant and soil 60 (1981), S. 325-339

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ISSN: 1573-5036

Keywords: Nutrient supply ; Nodule effectiveness ; Rhizobium competition ; Nodulation ; Lotus pedunculatus ; Lotus ; Rhizobium

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Summary The effect of nutrient supply on nodule formation and competition between Rhizobium strains for nodulation ofLotus pedunculatus was studied. Limiting plant growth by decreasing the supply of nutrients in an otherwise nitrogen-free medium, increased the size but decreased the number and the nitrogenase activity of nodules formed by a fast-growing strain of Lotus Rhizobium (NZP2037). In contrast decreasing nutrient supply caused only a small decline in the size, number and nitrogenase activity of nodules formed by a slow-growing strain (CC814s). Providing small quantities of NH4NO3 (50 to 250 μg N) to plants grown with a normal supply of other nutrients stimulated nodule development by both Rhizobium strains and increased the nitrogenase activity of the NZP2037 nodules. Differences in the level of effectiveness (nitrogen-fixing ability) of nodules formed by different Rhizobium strains on plants grown with a normal supply of nutrients were less apparent when the plants were grown with decreased nutrient supply or when the plants were supplied with low levels of inorganic N. Inter-strain competition for nodulation ofL. pedunculatus between the highly effective slow-growing strain CC814s and 7 other fast- and slow-growing strains, showed CC814s to form 42 to 100% of the nodules in all associations. The greater nodulating competitiveness of strain CC814s prevailed despite changes in the nutrient supply to the host plant. A tendency was observed for partially effective Lotus Rhizobium strains to become more competitive in nodule formation when plant growth was supplemented with low levels of inorganic nitrogen.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02149629

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5

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Biodiversity of soil microbial communities in agricultural systems (1996)

Pankhurst, C. E. ; Ophel-Keller, K. ; Doube, B. M. ; [et al.]

Springer

Biodiversity and conservation 5 (1996), S. 197-209

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ISSN: 1572-9710

Keywords: ecosystem function ; taxonomic diversity ; functional diversity ; nucleic acid analyses ; agricultural practices

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: The productivity and health of agricultural systems depend greatly upon the functional processes carried out by soil microorganisms and soil microbial communities. The biodiversity of the soil microbial communities and the effect of diversity on the stability of the agricultural system, is unknown. Taxonomic approaches to estimating biodiversity of soil microbial communities are limited by difficulties in defining suitable taxonomic units and the apparent non-culturability of the majority of the microbial species present in the soil. Analysis of functional diversity may be a more meaningful approach but is also limited by the need to culture organisms. Approaches which do not rely on culturing organisms such as fatty acid analysis and 16S/18S rRNA analysis have provided an insight into the extent of genetic diversity within communities and may be useful in the analysis of community structure. Scale effects, including successional processes associated with organic matter decomposition, local effects associated with abiotic soil factors, and regional effects including the effect of agricultural management practices, on the diversity of microbial communities are considered. Their impact is important in relation to the minimum biodiversity required to maintain system function.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00055830

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6

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Surface features of soybean root nodules (1975)

Pankhurst, C. E. ; Sprent, Janet I.

Springer

Protoplasma 85 (1975), S. 85-98

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ISSN: 1615-6102

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary The surface of turgid, nitrogen-fixing soybean root nodules is found to contain a number of prominent ridges on an otherwise smooth surface. Using the technique of critical point drying for tissue preparation, and scanning electron microscopy, these ridges were found to be lenticels, whose function is to permit the free movement of gases into and out of the nodule. The surface of the nodule between the lenticels contained no intercellular air spaces. The lenticels develop from a phellogen situated distal to a ring of sclereid cells in the nodule cortex. They develop as distinct “bands” of tissue immediately above and closely following the nodule vascular traces. When the nodules are subjected to conditions of water stress or waterlogging the most significant change to their surface is associated with the lenticels. In water stressed nodules the lenticel tissue collapses quickly, followed closely by shrinkage and collapse of the epidermis and outer cortex. In waterlogged nodules the lenticel tissues develop extensively with the production of large masses of loosely packed cells.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01567760

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7

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Mobilization of a Rhizobium meliloti megaplasmid carrying nodulation and nitrogen fixation genes into other rhizobia and Agrobacterium (1982)

Kondorosi, A. ; Kondorosi, E. ; Pankhurst, C. E. ; [et al.]

Springer

Molecular genetics and genomics 188 (1982), S. 433-439

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ISSN: 1617-4623

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary The indigenous megaplasmid pRme41b of Rhizobium meliloti 41 was made susceptible to mobilization with the P-1 type plasmid pJB3JI by inserting the mobilization (mob) region of RP4 into it. First the mob region together with a kanamycin resistance marker was inserted in vitro into a fragment of pRme41b cloned into pBR322. The recombinant plasmids so formed (pAK11 and pAK12) were then mobilized into R. meliloti. Since these recombinant plasmids were unable to replicate in R. meliloti, selection for kanamycin resistant derivatives allowed the isolation of pRme41b::pAK11 or pRme41b::pAK12 cointegrates. It was shown that in the majority of these recombinants, pAK11 or pAK12 was integrated into the homologous fragment of pRme41b. The pRme41b cointegrates were transferred into nod-nif deletion mutants of R. meliloti 41 where it was shown that both Nod+ and Fix+ phenotypes could be restored. The pRme41b cointegrates were also transferred into two other Rhizobium strains and into Agrobacterium tumefaciens. The Rhizobium strains and A. tumefaciens carrying pRme41b formed nodules of variable size on Medicago sativa roots, indicating that at least the early steps of nodulation of M. sativa are coded by pRme41b and are expressed in these bacteria.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00330045

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