• Journal of Korea Soil Environment Society
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• v.3 no.2
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• pp.71-78
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• 1998

Pyrene is a common petroleum contaminant. This compound is recalcitrant to biological degradation and persists long in contaminated environments. A microcosm experiment was conducted to investigate the degradation rate of pyrene in three different of soil : rhizosphere soil ; non-rhizosphere soil ; and sterilized soil. The degradation rate followed the order of rhizosphere soil)non-rhizosphere soil)sterilized soil. And the rate did not change significantly when organic acids commonly found in the rhizosphere were added to each soil but it seemed to be well related to the increase of the number of microorganisms. Overall, it appears that pyrene is degraded faster in the rhizosphere soil which has the higher microorganism density.

• Journal of Microbiology and Biotechnology
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• v.32 no.10
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• pp.1292-1298
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• 2022

Soil autotrophic bacterial communities play a significant role in the soil carbon (C) cycle in paddy fields, but little is known about how rhizosphere soil microorganisms respond to different long-term (35 years) fertilization practices under double rice cropping ecosystems in southern China. Here, we investigated the variation characteristics of rhizosphere soil RubisCO gene cbbL in the double rice ecosystems of in southern China where such fertilization practices are used. For this experiment we set up the following fertilizer regime: without any fertilizer input as a control (CK), inorganic fertilizer (MF), straw returning (RF), and organic and inorganic fertilizer (OM). We found that abundances of cbbL, 16S rRNA genes and RubisCO activity in rhizosphere soil with OM, RF and MF treatments were significantly higher than that of CK treatment. The abundances of cbbL and 16S rRNA genes in rhizosphere soil with OM treatment were 5.46 and 3.64 times higher than that of CK treatment, respectively. Rhizosphere soil RubisCO activity with OM and RF treatments increased by 50.56 and 45.22%, compared to CK treatment. Shannon and Chao1 indices for rhizosphere soil cbbL libraries with RF and OM treatments increased by 44.28, 28.56, 29.60, and 23.13% compared to CK treatment. Rhizosphere soil cbbL sequences with MF, RF and OM treatments mainly belonged to Variovorax paradoxus, uncultured proteobacterium, Ralstonia pickettii, Thermononospora curvata, and Azoarcus sp.KH33C. Meanwhile, cbbL-carrying bacterial composition was obviously influenced by soil bulk density, rhizosphere soil dissolved organic C, soil organic C, and microbial biomass C contents. Fertilizer practices were the principal factor influencing rhizosphere soil cbbL-carrying bacterial communities. These results showed that rhizosphere soil autotrophic bacterial communities were significantly changed under conditions of different long-term fertilization practices Therefore, increasing rhizosphere soil autotrophic bacteria community with crop residue and organic manure practices was found to be beneficial for management of double rice ecosystems in southern China.

• Korean Journal of Microbiology
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• v.12 no.1
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• pp.15-24
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• 1974

This experiment has been carried out with a view to elucidating the distribution of Azotobacter and their population size in rhizosphere and sea and designed ro compare the results with some environmental factors. Results of the experiment are summarized as follows: 1) It was observed that the population sizes of Azotobacter were decided upon the moisture content of soil and that the soil pH was one of the most impertant factors influencing the distribution of Azotobacter. 2)Population sizes of Azotobacter in rhizosphere were changed in accordance with the kinds of vegetation on soil: The rhizosphere where bamboo, corn, legume, and oak inhabit showed the largest population size of Azotobacter. On the other hand, rhizosphere of ginseng revealed no Azotobacter. However, the largest population of general fungi were measured at the rhizosphere. 3)Comparing the population sizes of general microbes in rhizosphere with those of non-rhizosphere, the population sizes of microbes in rhizosphere are larger than those of non-rhizosphere. 4)In coastal environments, population sizes of Azotobacter in surface water of sea are similar to those of the soil(mud) of tidal land. But the sizes are generally smaller than those of terrestrial soils.

• The Plant Pathology Journal
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• v.38 no.3
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• pp.203-211
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• 2022

Bacterial wilt, which is a major soil-borne disease with widespread occurrence, poses a severe danger in the field of tobacco production. However, there is very limited knowledge on bacterial wilt-induced microecological changes in the tobacco root system and on the interaction between Ralstonia solanacearum and fungal communities in the rhizosphere soil. Thus, in this study, changes in fungal communities in the rhizosphere soil of tobaccos with bacterial wilt were studied by 18S rRNA gene sequencing. The community composition of fungi in bacterial wilt-infected soil and healthy soil in two tobacco areas (Gengma and Boshang, Lincang City, Yunnan Province, China) was studied through the paired comparison method in July 2019. The results showed that there were significant differences in fungal community composition between the rhizosphere soil of diseased plants and healthy plants. The changes in the composition and diversity of fungal communities in the rhizosphere soil of tobaccos are vital characteristics of tobaccos with bacterial wilt, and the imbalance in the rhizosphere microecosystem of tobacco plants may further aggravate the disease.

• Environmental Engineering Research
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• v.12 no.2
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• pp.37-45
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• 2007

Phytoremediation has been used effectively for the biodegradation of oil-based contaminants, including diesel, by the stimulation of soil microbes near plant roots (rhizosphere). However, the technique has rarely been assessed for itsinfluence on soil microbial properties such as population, community structure, and diversity. In this study, the removal efficiency and characteristics of rhizobacteria for phytoremediation of diesel-contaminated soils were assessed using barnyard grass (Echinochloa crusgalli). The concentration of spiked diesel for treatments was around $6000\;mg\;kg^{-1}$. Diesel removal efficiencies reached 100% in rhizosphere soils, 76% in planted bulk soils, and 62% in unplanted bulk soils after 3weeks stabilization and 2 months growth(control, no microbial activity: 32%). The highest populations of culturable soil bacteria ($5.89{\times}10^8$ per g soil) and culturable hydrocarbon-degraders($5.65{\times}10^6$ per g soil) were found in diesel-contaminated rhizosphere soil, also yielding the highest microbial dehydrogenase. This suggests that the populations of soil bacteria, including hydrocarbon-degraders, were significantly increased by a synergistic rhizosphere + diesel effect. The diesel treatment alone resulted in negative population growth. In addition, we investigated the bacterial community structures of each soil sample based on DGGE (Denaturing Gel Gradient Electrophoresis) band patterns. Bacterial community structure was most influenced by the presence of diesel contamination (76.92% dissimilarity to the control) and by a diesel + rhizosphere treatment (65.62% dissimilarity), and least influenced by the rhizosphere treatment alone (48.15% dissimilarity). Based on the number of distinct DGGE bands, the bacterial diversity decreased with diesel treatment, but kept constant in the rhizosphere treatment. The rhizosphere thus positively influenced bacterial population density in diesel-contaminated soil, resulting in high removal efficiency of diesel.

• The Korean Journal of Ecology
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• v.22 no.1
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• pp.7-11
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• 1999

The measurement of pH in the rhizosphere soil was conducted to clarify whether the growth of pokeberry plants affect the acidity of rhizosphere soil in two environmentally contrasting area Ulsan and Chongju city. The rhizosphere pH between 5.25 and 5.33 was shown in the pokeberry stand at Mt. Boomo located at Chongju. The rhizosphere pH of pokeberry stands at Mt. Bongdae, Mt. Sinsun and Mt. Totchil was below 5.0, and did not differ with depth and distance from the main axis of root. At Mt. Bongdae, however, the pH in the rhizosphere soil was significantly changed with soil depths though that was not changed horizontally. The rhizosphere pH at top soil was lower than that at subsoil, which indicates the fact that soil acidification at Mt. Bongdae was not caused by pokeberry plants. Furthermore, the rhizosphere pH did not change with the growth of pokeberry plants. These results indicate that the hypothesis that pokeberry plants acidify local soil environment should be reconsidered.

• Mycobiology
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• v.49 no.4
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• pp.346-354
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• 2021

The genus Aspergillus is commonly isolated from various marine and terrestrial environments; however, only a few species have been studied in rhizosphere soil. As part of the Korean indigenous fungal excavation project, we investigated fungal diversity from rhizosphere soil, focusing on Aspergillus species. A total of 13 strains were isolated from the rhizosphere soil of three different plants. Based on phylogenetic analysis of β-tubulin and calmodulin and morphological characteristics, we identified five Aspergillus species. A. calidoustus and A. pseudodeflectus were commonly isolated from the rhizosphere soil. Four species were confirmed as unrecorded species in Korea: A. calidoustus, A. dimorphicus, A. germanicus, and A. pseudodeflecuts. The detailed morphological descriptions of these unrecorded species are provided.

• Mycobiology
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• v.48 no.6
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• pp.431-442
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• 2020

Penicillium, the most common genus plays an important ecological role in various terrestrial and marine environments. However, only a few species have been reported from rhizosphere soil. As part of a project to excavate Korean indigenous fungi, we investigated rhizosphere soil of six plants in the forest (terrestrial habitat) and sand dunes (coastal habitat) and focused on discovering Penicillium species. A total of 64 strains were isolated and identified as 26 Penicillium species in nine sections based on morphological characteristics and the sequence analysis of β-tubulin and calmodulin. Although this is a small-scale study in a limited rhizosphere soil, eight unrecorded species and four potential new species have been identified. In addition, most Penicillium species from rhizosphere soil were unique to each plant. Penicillium halotolerans, P. scabrosum, P. samsonianum, P. jejuense, and P. janczewskii were commonly isolated from rhizosphere soil. Eight Penicillium species, P. aurantioviolaceum, P. bissettii, P. cairnsense, P. halotolerans, P. kananaskense, P. ortum, P. radiatolobatum, and P. verhagenii were recorded for the first time in Korea. Here, we provide the detailed morphological description of these unrecorded species.

• Korean Journal of Soil Science and Fertilizer
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• v.45 no.5
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• pp.798-804
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• 2012

Although siderophores are induced primarily in response to iron deficiency, soil and other ecological factors can affect on this process. This study was to evaluate the production of siderophores by different fungal species isolated from heavy metal contaminated and uncontaminated soils. More than thirty fungal strains were isolated from heavy metal contaminated and rhizosphere uncontaminated soils. Chrome azurol sulfonate (CAS) was used for both quantitative and qualitative evaluation of siderophores production. No significant correlations were observed between the tested variables such as ultraviolet (UV) irradiation method and CAS-agar plate and heavy metal concentration in both soils. The production of siderophores in rhizosphere fungi was higher than those isolated from the contaminated soil; however, the difference was not significant. The siderophore production (%) by fungi isolated from heavy metal contaminated soil using UV irradiation method was positively correlated with the qualitative values using CAS-plate method (P<0.05). Pearson correlation test indicated a positive correlation between the quantitative and qualitative methods of detection for fungi isolated from rhizosphere and also those isolated from heavy metal contaminated soil.

• Journal of Microbiology and Biotechnology
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• v.13 no.2
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• pp.236-242
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• 2003

A culture-independent and -dependent survey of the bacterial community structure in the rhizosphere and soil samples from hot pepper plants was conducted using 16S rDNA clone library and FAME analyses. Out of the 78 clones sequenced, 56% belonged to Proteobacteria, 4% to high G+C Gram- positive group, 3% to Cytophyga-Flexibacter-Bacreroides, and 32% could not be grouped with any known taxonomic division. Among the 127 FAME isolates identified, 66% belonged to low G+C Gram-positive bacteria (Baciilus spp.) and 26% to high G+C Gram-positive bacteria. In a cluster analysis, the results for both methods were found to be strikingly dissimilar. The current study is the first comparative study of FAME and 165 rDNA clonal analyses performed on the same set of soil, rhizosphere soil, and root samples.