Dataset Information

Survival and Competitiveness of Bradyrhizobium japonicum Strains 20 Years after Introduction into Field Locations in Poland.

ABSTRACT: It was previously demonstrated that there are no indigenous strains of Bradyrhizobium japonicum forming nitrogen-fixing root nodule symbioses with soybean plants in arable field soils in Poland. However, bacteria currently classified within this species are present (together with Bradyrhizobium canariense) as indigenous populations of strains specific for nodulation of legumes in the Genisteae tribe. These rhizobia, infecting legumes such as lupins, are well established in Polish soils. The studies described here were based on soybean nodulation field experiments, established at the Pozna? University of Life Sciences Experiment Station in Gorzy?, Poland, and initiated in the spring of 1994. Long-term research was then conducted in order to study the relation between B. japonicum USDA 110 and USDA 123, introduced together into the same location, where no soybean rhizobia were earlier detected, and nodulation and competitive success were followed over time. Here we report the extra-long-term saprophytic survival of B. japonicum strains nodulating soybeans that were introduced as inoculants 20 years earlier and where soybeans were not grown for the next 17 years. The strains remained viable and symbiotically competent, and molecular and immunochemical methods showed that the strains were undistinguishable from the original inoculum strains USDA 110 and USDA 123. We also show that the strains had balanced numbers and their mobility in soil was low. To our knowledge, this is the first report showing the extra-long-term persistence of soybean-nodulating strains introduced into Polish soils and the first analyzing the long-term competitive relations of USDA 110 and USDA 123 after the two strains, neither of which was native, were introduced into the environment almost 2 decades ago.

SUBMITTER: Narozna D

PROVIDER: S-EPMC4510166 | biostudies-literature | 2015 Aug

REPOSITORIES: biostudies-literature

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Survival and Competitiveness of Bradyrhizobium japonicum Strains 20 Years after Introduction into Field Locations in Poland.

Narożna Dorota D Pudełko Krzysztof K Króliczak Joanna J Golińska Barbara B Sugawara Masayuki M Mądrzak Cezary J CJ Sadowsky Michael J MJ

Applied and environmental microbiology 20150605 16

It was previously demonstrated that there are no indigenous strains of Bradyrhizobium japonicum forming nitrogen-fixing root nodule symbioses with soybean plants in arable field soils in Poland. However, bacteria currently classified within this species are present (together with Bradyrhizobium canariense) as indigenous populations of strains specific for nodulation of legumes in the Genisteae tribe. These rhizobia, infecting legumes such as lupins, are well established in Polish soils. The stud ...[more]

PMID: 26048934

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Project description:Soybean is the most important legume cropped worldwide and can highly benefit from the biological nitrogen fixation (BNF) process. Brazil is recognized for its leadership in the use of inoculants and two strains, Bradyrhizobium japonicum CPAC 15 (=SEMIA 5079) and Bradyrhizobium diazoefficiens CPAC 7 (=SEMIA 5080) compose the majority of the 70 million doses of soybean inoculants commercialized yearly in the country. We studied a collection of natural variants of these two strains, differing in properties of competitiveness and efficiency of BNF. We sequenced the genomes of the parental strain SEMIA 566 of B. japonicum, of three natural variants of this strain (S 204, S 340 and S 370), and compared with another variant of this group, strain CPAC 15. We also sequenced the genome of the parental strain SEMIA 586 of B. diazoefficiens, of three natural variants of this strain (CPAC 390, CPAC 392 and CPAC 394) and compared with the genome of another natural variant, strain CPAC 7. As the main genes responsible for nodulation (nod, noe, nol) and BNF (nif, fix) in soybean Bradyrhizobium are located in symbiotic islands, our objective was to identify genetic variations located in this region, including single nucleotide polymorphisms (SNPs) and insertions and deletions (indels), that could be potentially related to their different symbiotic phenotypes. We detected 44 genetic variations in the B. japonicum strains and three in B. diazoefficiens. As the B. japonicum strains have gone through a longer period of adaptation to the soil, the higher number of genetic variations could be explained by survival strategies under the harsh environmental conditions of the Brazilian Cerrado biome. Genetic variations were detected in genes enconding proteins such as a dephospho-CoA kinase, related to the CoA biosynthesis; a glucosamine-fructose-6-phosphate aminotransferase, key regulator of the hexosamine biosynthetic pathway; a LysR family transcriptional regulator related to nodulation genes; and NifE and NifS proteins, directly related to the BNF process. We suggest potential genetic variations related to differences in the symbiotic phenotypes.

Project description:BACKGROUND:The soybean-Bradyrhizobium symbiosis can be highly efficient in fixing nitrogen, but few genomic sequences of elite inoculant strains are available. Here we contribute with information on the genomes of two commercial strains that are broadly applied to soybean crops in the tropics. B. japonicum CPAC 15 (=SEMIA 5079) is outstanding in its saprophytic capacity and competitiveness, whereas B. diazoefficiens CPAC 7 (=SEMIA 5080) is known for its high efficiency in fixing nitrogen. Both are well adapted to tropical soils. The genomes of CPAC 15 and CPAC 7 were compared to each other and also to those of B. japonicum USDA 6T and B. diazoefficiens USDA 110T. RESULTS:Differences in genome size were found between species, with B. japonicum having larger genomes than B. diazoefficiens. Although most of the four genomes were syntenic, genome rearrangements within and between species were observed, including events in the symbiosis island. In addition to the symbiotic region, several genomic islands were identified. Altogether, these features must confer high genomic plasticity that might explain adaptation and differences in symbiotic performance. It was not possible to attribute known functions to half of the predicted genes. About 10% of the genomes was composed of exclusive genes of each strain, but up to 98% of them were of unknown function or coded for mobile genetic elements. In CPAC 15, more genes were associated with secondary metabolites, nutrient transport, iron-acquisition and IAA metabolism, potentially correlated with higher saprophytic capacity and competitiveness than seen with CPAC 7. In CPAC 7, more genes were related to the metabolism of amino acids and hydrogen uptake, potentially correlated with higher efficiency of nitrogen fixation than seen with CPAC 15. CONCLUSIONS:Several differences and similarities detected between the two elite soybean-inoculant strains and between the two species of Bradyrhizobium provide new insights into adaptation to tropical soils, efficiency of N2 fixation, nodulation and competitiveness.

Dataset Information

Survival and Competitiveness of Bradyrhizobium japonicum Strains 20 Years after Introduction into Field Locations in Poland.

Publications

Survival and Competitiveness of Bradyrhizobium japonicum Strains 20 Years after Introduction into Field Locations in Poland.

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