Hidden diversity of double-stranded DNA phages in symbiotic Rhizobium species

In this study, we addressed the extent of diversification of phages associated with nitrogen-fixing symbiotic Rhizobium species. Despite the ecological and economic importance of the Rhizobium genus, little is known about the diversity of the associated phages. A thorough assessment of viral diversity requires investigating both lytic phages and prophages harboured in diverse Rhizobium genomes. Protein-sharing networks identified 56 viral clusters (VCs) among a set of 425 isolated phages and predicted prophages. The VCs formed by phages had more proteins in common and a higher degree of synteny, and they group together in clades in the associated phylogenetic tree. By contrast, the VCs of prophages showed significant genetic variation and gene loss, with selective pressure on the remaining genes. Some VCs were found in various Rhizobium species and geographical locations, suggesting that they have wide host ranges. Our results indicate that the VCs represent distinct taxonomic units, probably representing taxa equivalent to genera or even species. The finding of previously undescribed phage taxa indicates the need for further exploration of the diversity of phages associated with Rhizobium species. This article is part of the theme issue ‘The secret lives of microbial mobile genetic elements’.

EFFECTS OF PHOSPHORUS AVAILABILITY ON NODULATION AND NITROGEN UPTAKE BY THREE LEGUME CROPS IN TWO GHANAIAN SOILS

Purpose: A greenhouse study of Soybean, Cowpea and Pigeon Pea was made at University of Ghana, to determine the effects of phosphorus availability on nodulation and nitrogen uptake by the afore mentioned legumes in two Ghanaian soils, Adenta and Nzema series. Methodology: Three P rates of 0mg, 50mg and 100mg P of TSP and TPR were applied to a kilogram of soil per pot in two soil series. The pots were arranged using Randomized Complete Block Design. GenstatR was used to do the statistical analysis. Findings: The results from this study showed that with or without Triple Super Phosphate (TSP) or Togo Phosphate Rock (TPR), soybean did not form nodules in the Nzema soil but nodulated with TSP application in the Adenta soil. The absence of nodulation even with high P from TSP by soybean in Nzema soil is surprising but the observation in the Nzema soil may be attributed to the absence of soybean Rhizobium cells or insignificant numbers of these rhizobia. The results of the present data indicated that treatments with higher P application gave higher N uptake and showed the link among P application, high nodule dry weight, and N uptake. The improvement in the dry matter yield of pigeon pea and cowpea on Adenta soil and soybean on the Nzema soil at TPR50 and TPR100 show the importance of P application to dry matter yield of legumes. Significant difference that was shown by cowpea on Nzema soil could be attributed to the ability of the crop to desorp P from sparingly available P sources through exudation of high amounts of organic acid anions, mainly citrate. Unique contributions to theory, practice and policy: In the soil, Rhizobium species must recognize their specific host before nodulation may take place and the absence of the appropriate Rhizobium species with the introduction of a legume into a given soil may result in no or poor nodulation. Low P availability is a challenge for crop species to nodulate since the rhizobia responsible for nitrogen fixation have a high P requirement. The toxicity of Aluminum to rhizobia may be due to inhibition of DNA replication because of binding of Aluminum to DNA. One factor that could have accounted for the better nodulation in soil is the higher acidity. The optimum pH for effective rhizobia growth in soils is between pH 6 and 7.

EFFECTS OF PHOSPHORUS AVAILABILITY ON NODULATION AND NITROGEN UPTAKE BY THREE LEGUME CROPS IN TWO GHANAIAN SOILS

Purpose: A greenhouse study of Soybean, Cowpea and Pigeon Pea was made at University of Ghana, to determine the effects of phosphorus availability on nodulation and nitrogen uptake by the afore mentioned legumes in two Ghanaian soils, Adenta and Nzema series. Methodology: Three P rates of 0mg, 50mg and 100mg P of TSP and TPR were applied to a kilogram of soil per pot in two soil series. The pots were arranged using Randomized Complete Block Design. GenstatR was used to do the statistical analysis. Findings: The results from this study showed that with or without Triple Super Phosphate (TSP) or Togo Phosphate Rock (TPR), soybean did not form nodules in the Nzema soil but nodulated with TSP application in the Adenta soil. The absence of nodulation even with high P from TSP by soybean in Nzema soil is surprising but the observation in the Nzema soil may be attributed to the absence of soybean Rhizobium cells or insignificant numbers of these rhizobia. The improvement in the dry matter yield of pigeon pea and cowpea on Adenta soil and soybean on the Nzema soil at TPR50 and TPR100 show the importance of P application to dry matter yield of legumes. Significant difference that was shown by cowpea on Nzema soil could be attributed to the ability of the crop to desorp P from sparingly available P sources through exudation of high amounts of organic acid anions, mainly citrate. Unique contributions to theory, practice and policy: In the soil, Rhizobium species must recognize their specific host before nodulation may take place and the absence of the appropriate Rhizobium species with the introduction of a legume into a given soil may result in no or poor nodulation. Low P availability is a challenge for crop species to nodulate since the rhizobia responsible for nitrogen fixation have a high P requirement. The toxicity of Aluminum to rhizobia may be due to inhibition of DNA replication because of binding of Aluminum to DNA. One factor that could have accounted for the better nodulation in soil is the higher acidity. The optimum pH for effective rhizobia growth in soils is between pH 6 and 7.

EFFECTS OF PHOSPHORUS AVAILABILITY ON NODULATION AND NITROGEN UPTAKE BY THREE LEGUME CROPS IN TWO GHANAIAN SOILS

Purpose: A greenhouse study of Soybean, Cowpea and Pigeon Pea was made at University of Ghana, to determine the effects of phosphorus availability on nodulation and nitrogen uptake by the afore mentioned legumes in two Ghanaian soils, Adenta and Nzema series. Methodology: Three P rates of 0mg, 50mg and 100mg P of TSP and TPR were applied to a kilogram of soil per pot in two soil series. The pots were arranged using Randomized Complete Block Design. GenstatR was used to do the statistical analysis. Findings: The results from this study showed that with or without Triple Super Phosphate (TSP) or Togo Phosphate Rock (TPR), soybean did not form nodules in the Nzema soil but nodulated with TSP application in the Adenta soil. The absence of nodulation even with high P from TSP by soybean in Nzema soil is surprising but the observation in the Nzema soil may be attributed to the absence of soybean Rhizobium cells or insignificant numbers of these rhizobia. The improvement in the dry matter yield of pigeon pea and cowpea on Adenta soil and soybean on the Nzema soil at TPR50 and TPR100 show the importance of P application to dry matter yield of legumes. Significant difference that was shown by cowpea on Nzema soil could be attributed to the ability of the crop to desorp P from sparingly available P sources through exudation of high amounts of organic acid anions, mainly citrate. Unique contributions to theory, practice and policy: In the soil, Rhizobium species must recognize their specific host before nodulation may take place and the absence of the appropriate Rhizobium species with the introduction of a legume into a given soil may result in no or poor nodulation. Low P availability is a challenge for crop species to nodulate since the rhizobia responsible for nitrogen fixation have a high P requirement. The toxicity of Aluminum to rhizobia may be due to inhibition of DNA replication because of binding of Aluminum to DNA. One factor that could have accounted for the better nodulation in soil is the higher acidity. The optimum pH for effective rhizobia growth in soils is between pH 6 and 7.

EFFECTS OF PHOSPHORUS AVAILABILITY ON NODULATION AND NITROGEN UPTAKE BY THREE LEGUME CROPS IN TWO GHANAIAN SOILS

Purpose: A greenhouse study of Soybean, Cowpea and Pigeon Pea was made at University of Ghana, to determine the effects of phosphorus availability on nodulation and nitrogen uptake by the afore mentioned legumes in two Ghanaian soils, Adenta and Nzema series. Methodology: Three P rates of 0mg, 50mg and 100mg P of TSP and TPR were applied to a kilogram of soil per pot in two soil series. The pots were arranged using Randomized Complete Block Design. GenstatR was used to do the statistical analysis. Findings: The results from this study showed that with or without Triple Super Phosphate (TSP) or Togo Phosphate Rock (TPR), soybean did not form nodules in the Nzema soil but nodulated with TSP application in the Adenta soil. The absence of nodulation even with high P from TSP by soybean in Nzema soil is surprising but the observation in the Nzema soil may be attributed to the absence of soybean Rhizobium cells or insignificant numbers of these rhizobia. The improvement in the dry matter yield of pigeon pea and cowpea on Adenta soil and soybean on the Nzema soil at TPR50 and TPR100 show the importance of P application to dry matter yield of legumes. Significant difference that was shown by cowpea on Nzema soil could be attributed to the ability of the crop to desorp P from sparingly available P sources through exudation of high amounts of organic acid anions, mainly citrate. Unique contributions to theory, practice and policy: In the soil, Rhizobium species must recognize their specific host before nodulation may take place and the absence of the appropriate Rhizobium species with the introduction of a legume into a given soil may result in no or poor nodulation. Low P availability is a challenge for crop species to nodulate since the rhizobia responsible for nitrogen fixation have a high P requirement. The toxicity of Aluminum to rhizobia may be due to inhibition of DNA replication because of binding of Aluminum to DNA. One factor that could have accounted for the better nodulation in soil is the higher acidity. The optimum pH for effective rhizobia growth in soils is between pH 6 and 7

Effect of some environmental conditions on the growth of rhizobium species

Rhizobium species are involved in symbiotic relationship which can be exploited in agriculture to enhance crop and pasture growth without the addition of nitrogen fertilizers. However, a number of environmental factors are known to affect the symbiotic efficiency of Rhizobium. This current study evaluated tolerance of Rhizobium species isolated from root nodules of cowpea obtained from Akure, Nigeria to variation in temperature, pH levels, salt concentrations, heavy metals as well as antibiotics. Three Rhizobium species were isolated from root nodules of Vignaunguiculata and Phaseolus vulgaris after 34 days of planting yeast extract mannitol agar (YEMA). Their tolerance to environmental factors such as temperature, pH, sodium chloride, heavy metals as well as antibiotics was determined. All the isolates grew very well at 28oC, moderately at 37oC but their growth was hampered at 50o C. Maximal growth was observed at neutral pH. However, Sinorhizobium sp showed high tolerance to pH 7.0. Also, the isolates showed high tolerance to low concentration of sodium chloride (0.1%) and heavy metals with reduction in their optical density at higher concentrations. Rhizobium sp showed high level of tolerance at 4% compared to Mesorhizobium sp. and Sinorhizobium sp. Rhizobium spp. showed resistance to all the antibiotics investigated while Mesorhizobium sp. was sensitive to only to pefloxacin and sparfloxacin, while Sinorhizobium sp. was only sensitive to pefloxacin. The isolates in this study can be assessed for their suitability as inoculants forcowpea in soils below temperature 50oC and at neutral pH. J. bio-sci. 26: 15-24, 2018