A New Hypothesis on the Strategy for Acquisition of Phosphorus in Arbuscular Mycorrhiza : Up-Regulation of Secreted Acid Phosphatase Gene in the Host Plant

The mycorrhiza-responsive phosphatase of Tagetes patula in symbiosis with Glomus etunicatum was detected by electrophoresis, was purified by column chromatography, and was characterized as acid phosphatase that was secreted into rhizosphere. The N-terminal amino acid sequence was determined by a gas-phase sequencer, and a cDNA fragment of the phosphatase gene (TpPAP1) was amplified by degenerate primers designed based on the N-terminal amino acid sequence. The full-length cDNA was obtained by the rapid amplification of cDNA ends technique. The TpPAP1 was of host origin, and the cDNA was 1,843 bp long with a predicted open reading frame of polypeptide of 466 amino acids. Phylogenetic analysis revealed that the gene fell into the cluster of plant high-molecular-weight purple acid phosphatase. Expression analysis of the TpPAP1 in T. patula in symbiosis with Archaeospora leptoticha showed that the levels of transcripts increased eightfold by mycorrhizal colonization. Western blot analysis revealed that the 57-kDa protein corresponding to the mycorrhiza- responsive phosphatase increased by mycorrhizal colonization. The present study proposes a new strategy for acquisition of P in arbuscular mycorrhizal associations in which the fungal partner activates a part of the low-P adaptation system of the plant partner, phosphatase secretion, and improves the overall efficiency of P uptake

Irrigation with oxygen-nanobubble water can reduce methane emission and arsenic dissolution in a flooded rice paddy

A remarkable feature of nanobubbles (<10 ^–6 m in diameter) is their long lifetime in water. Supplying oxygen-nanobubbles (NBs) to continuously flooded paddy soil may retard the development of reductive conditions, thereby reducing the emission of methane (CH _4 ), a potent greenhouse gas, and dissolution of arsenic, an environmental load. We tested this hypothesis by performing a pot experiment and measuring redox-related variables. The NBs were introduced into control water (with properties similar to those of river water) using a commercially available generator. Rice ( Oryza sativa L.) growth did not differ between plants irrigated with NB water and those irrigated with control water, but NB water significantly ( p  < 0.05) reduced cumulative CH _4 emission during the rice-growing season by 21%. The amounts of iron, manganese, and arsenic that leached into the drainage water before full rice heading were also reduced by the NB water. Regardless of the water type, weekly-measured CH _4 flux was linearly correlated with the leached iron concentration during the rice-growing season ( r  = 0.74, p  < 0.001). At the end of the experiment, the NB water significantly lowered the soil pH in the 0–5 cm layer, probably because of the raised redox potential. The population of methanogenic Archaea ( mcrA copy number) in the 0–5 cm layer was significantly increased by the NB water, but we found no correlation between the mcrA copy number and the cumulative CH _4 emission ( r  = –0.08, p  = 0.85). In pots without rice plants, soil reduction was not enhanced, regardless of the water type. The results indicate that NB water reduced CH _4 emission and arsenic dissolution through an oxidative shift of the redox conditions in the flooded soil. We propose the use of NB water as a tool for controlling redox conditions in flooded paddy soils

Data from: Insecticide applications to soil contribute to development of Burkholderia mediating insecticide resistance in stinkbugs

Some soil Burkholderia strains are capable of degrading the organophosphorus insecticide, fenitrothion, and establish symbiosis with stinkbugs, making the host insects fenitrothion-resistant. However, the ecology of the symbiotic degrading Burkholderia adapting to fenitrothion in the free-living environment is unknown. We hypothesized that fenitrothion applications affect the dynamics of fenitrothion-degrading Burkholderia, thereby controlling the transmission of symbiotic degrading Burkholderia from the soil to stinkbugs. We investigated changes in the density and diversity of culturable Burkholderia (i.e. symbiotic and nonsymbiotic fenitrothion degraders and nondegraders) in fenitrothion-treated soil using microcosms. During the incubation with five applications of pesticide, the density of the degraders increased from less than the detection limit to around 106/g of soil. The number of dominant species among the degraders declined with the increasing density of degraders; eventually, one species predominated. This process can be explained according to the competitive exclusion principle using Vmax and Km values for fenitrothion metabolism by the degraders. We performed a phylogenetic analysis of representative strains isolated from the microcosms and evaluated their ability to establish symbiosis with the stinkbug Riptortus pedestris. The strains that established symbiosis with R. pedestris were assigned to a cluster including symbionts commonly isolated from stinkbugs. The strains outside the cluster could not necessarily associate with the host. The degraders in the cluster predominated during the initial phase of degrader dynamics in the soil. Therefore, only a few applications of fenitrothion could allow symbiotic degraders to associate with their hosts and may cause the emergence of symbiont-mediated insecticide resistance

Comparison of the Effects of Phenylhydrazine Hydrochloride and Dicyandiamide on Ammonia-Oxidizing Bacteria and Archaea in Andosols

Dicyandiamide, a routinely used commercial nitrification inhibitor (NI), inhibits ammonia oxidation catalyzed by ammonia monooxygenase (AMO). Phenylhydrazine hydrochloride has shown considerable potential for the development of next-generation NIs targeting hydroxylamine dehydrogenase (HAO). The effects of the AMO inhibitor and the HAO inhibitor on ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) present in agricultural soils have not been compared thus far. In the present study, the effects of the two inhibitors on soil nitrification and the abundance of AOA and AOB as well as their community structure were investigated in a soil microcosm using quantitative polymerase chain reaction and pyrosequencing. The net nitrification rates and the growth of AOA and AOB in this soil microcosm were inhibited by both NIs. Both NIs had limited effect on the community structure of AOB and no effect on that of AOA in this soil microcosm. The effects of phenylhydrazine hydrochloride were similar to those of dicyandiamide. These results indicated that organohydrazine-based NIs have potential for the development of next-generation NIs targeting HAO in the future