The effects of radiation pollution on the population diversities and metabolic characteristics in soil microorganisms from radiation pollution areas were investigated. Microbial diversities were determined by using methods of cultured isolates and carbon source utilization on Biolog EcoPlate™. The results showed that radiation changed soil microbial community structure and function. With the increasing of radiation pollution, the number of bacteria and actinomycetes declined gradually. Carbon utilizations of microbial community were significant ly different from each other (ρ < 0.05). Microbial activity decreased gradually; Simpson index and McIntosh index increased, but Shannon-Wiener index was not significant different; the major utilized substrates indicated that microbes more tend to use carboxylic acids and polymers as carbon sources, instead of carbohydrates. In conclusion, the community composition of microorganisms as well as population diversity in soils was impacted obviously by radiation pollution.

Metalaxyl, an important phenylamide fungicide, is widely used for controlling fungal diseases caused by pathogens of the orders Peronosporales and Pythiales. Under laboratory conditions, metalaxyl was applied to soil samples at the recommended field rate (1×FR) and double of recommended field rate (2×FR) for two and three times. Soil subsamples were taken at 0, 1, 3, 7, 14, 28, and 45 days after the last application of metalaxyl for determination of metalaxyl residues and 7, 14, 28, and 56 days for enumeration of cultivable microorganisms and DGGE profile of soil microbial community. Soil incubation experiments revealed that metalaxyl was degraded faster in the third application than in the second application of the fungicide, half-lives of metalaxyl decreasing from 16.2 to 9.9 days for recommended field rate and 22.1 to 20.0 days for double of recommended field rate. Soil bacterial and fungal populations decreased in the first 14 days and then recovered to the control levels; population of actinomycetes did not alter in the first 28 days but increased at the end of the experiment after the second application. However, after the third treatment, temporary increase in soil bacteria population, nonsignificant inhibition effect on fungal population, and obvious stimulation effect on actinomycetes number were observed. DGGE results showed that successive inputs of metalaxyl altered the bacterial community structure. There were differences in the persistence and effects of metalaxyl on microbial community between the second and the third metalaxyl treatments.

Bacteria, actinomycetes, and fungi are the dominant components of the soil microflora, and some of their species can perform denitrification. The aim of this study was to investigate the interactions of three kinds of denitrifiers in mix-culturing systems. Three denitrifying strains, i.e., one bacterial strain (strain B5), one actinomycete strain (strain A2), and one fungal strain (strain F1), were isolated from a rice paddy soil. Denitrifier interactions were examined by analyzing the population dynamics and metabolic substance in the mix-culturing systems with two and three strains and by estimating the effects of cell-free culture filtrates on the strains. Results showed that the growth of B5 was enhanced by F1 and A2, respectively, and nitrate removal proportions in the culture systems increased from 52% (B5) to 64% (B5 + F1) and 67% (B5 + A2), and the nitrate removal was further enhanced in the three strain mix-culturing system (74%, A2 + F1 + B5). Strain B5 stimulated the cell growth of A2 directly and indirectly. The existence of A2 was lethal for cell growth of F1, while A2 was also suppressed by F1. The suppressive interaction reduced nitrate removal rates from the single systems of 12.8 (F1) and 11.5 mg L−1 day−1 (A2) to 8.75 mg L−1 day−1 (A2 + F1). Likewise, F1 was inhibited by B5. The results also showed that the cell-free culture filtrates of other strains suppressed the cell growth of B5 and F1, respectively, but enhanced the cell growth of A2. In addition to the direct effect of cell-free culture filtrates, other indirect relationships could affect the denitrifier spatial distributions and balance of the suppression or promotion effects, which were beneficial to maintain the microbial structure and function stability with a low nitrous oxide emission in the soil.

Enzyme activity and microbial population in soils have important roles in keeping soil fertility. ZJ0273 is a novel pyrimidynyloxybenzoic-based herbicide, which was recently developed in China. The effect of ZJ0273 on soil enzyme activity and microbial population in two different soils was investigated in this study for the first time. The protease activity was significantly inhibited by ZJ0273 and this inhibiting effect gradually weakened after 60-day incubation. The results also showed that ZJ0273 had different stimulating effects on the activities of dehydrogenase, urease, and catalase. Dehydrogenase was consistently stimulated by all the applied concentrations of ZJ0273. The stimulating effect on urease weakened after 60-day incubation. Catalase activity was subject to variations during the period of the experiments. The results of microbial population showed that the number of bacteria and actinomycetes increased in ZJ0273-treated soil compared with the control after 20 days of incubation, while fungal number decreased after only 10 days of incubation in soils. DT50 (half-life value) and k (degradation rate constant) of ZJ0273 in S1 (marine-fluvigenic yellow loamy soil) and S2 (Huangshi soil) were found 69.31 and 49.50 days and 0.010 and 0.014 day⁻¹, respectively.

The aim of this work was to evaluate the bioremediation potential of microorganisms from intertidal sediments of a sandy beach affected by a major oil spill 7 years before and subject to chronic petroleum contamination since then. For that, the response of microorganisms to a new oil contamination was assessed in terms of community structure, abundance, and capacity to degrade hydrocarbons. Experiments were carried out under laboratory-controlled conditions by mixing sediment with crude oil with three different nitrogen supplementations in 50 ml serum bottles under constant shake for 15 days. Autochthonous microorganisms were able to respond to the new oil contamination by increasing their abundance (quantified by DAPI) and changing the community structure (evaluated by DGGE). This response was particularly clear for some specific bacterial groups such as Pseudomonas, Actinomycetales, and Betaproteobacteria. These communities presented an important potential for hydrocarbon degradation (up to 85 % for TPHs and 70 % for total PAHs), being the biodegradation stimulated by addition of an appropriate amount of nitrogen.

Introduction Chlorimuron-ethyl has been widely used for the soybean production of China, but less information is available on the possible risk of long-term application of this herbicide. Materials and methods In this paper, soil samples were collected from the plots having been received 30 g active component of chlorimuron-ethyl/ha per year for 5 and 10 years in a continuously cropped soybean field of Northeast China, with their microbial community analyzed by plate counting, PCR-DGGE, and cloning library. Chlorimuron-ethyl had a higher accumulation in test soils, and the accumulation decreased the CFU of soil bacteria and increased the CFU of soil fungi significantly. The CFU of soil actinomycetes only had a significant decrease in the plot having been received chlorimuron-ethyl for 10 years. Results and discussion Under the long-term stress of chlorimuron-ethyl, the diversity and evenness of soil microbial community decreased, and more importantly, some bacterial and fungal species that possibly benefited soybean's growth, e.g., Acidobacteria, γ-proteobacteria, Cortinarius violaceu, Acarospora smaragdula, and Xerocomus chrysenteron decreased or demised, while some species that could induce the obstacle of soybean's continuous cropping, e.g., Fusarium oxysporum, Rhizoctonia solani, and Phytophthora sojae, increased or appeared. Some actinomycetes were inhibited having negative effects on the antagonism between soil microbes. It is considered that due to the longer half-life of chlorimuron-ethyl in soil and the resistance and resilience of soil microbes to short-term environmental stress, long-term in situ investigation rather than laboratory microcosm test or short-term field experiment would be more appropriate to the accurate assessment of the ecological risk of long-term chlorimuron-ethyl application. Further studies should be made on the application mode and duration of chlorimuron-ethyl to reduce the possible ecological risk of applying this herbicide on continuously cropped soybean field.

Background, aim, and scope Soil contamination with heavy metals occurs as a result of both anthropogenic and natural activities. Heavy metals could have long-term hazardous impacts on the health of soil ecosystems and adverse influences on soil biological processes. Soil enzymatic activities are recognized as sensors towards any natural and anthropogenic disturbance occurring in the soil ecosystem. Similarly, microbial biomass carbon (MBC) is also considered as one of the important soil biological activities frequently influenced by heavy metal contamination. The polymerase chain reaction-denaturing gradient gel electrophoresis (DGGE) has recently been used to investigate changes in soil microbial community composition in response to environmental stresses. Soil microbial community structure and activities are difficult to elucidate using single monitoring approach; therefore, for a better insight and complete depiction of the soil microbial situation, different approaches need to be used. This study was conducted in a greenhouse for a period of 12 weeks to evaluate the changes in indigenous microbial community structure and activities in the soil amended with different application rates of Cd, Pb, and Cd/Pb mix. In a field environment, soil is contaminated with single or mixed heavy metals; so that, in this research, we used the selected metals in both single and mixed forms at different application rates and investigated their toxic effects on microbial community structure and activities, using soil enzyme assays, plate counting, and advanced molecular DGGE technique. Soil microbial activities, including acid phosphatase (ACP), urease (URE), and MBC, and microbial community structure were studied. Materials and methods A soil sample (0-20 cm) with an unknown history of heavy metal contamination was collected and amended with Cd, Pb, and Cd/Pb mix using the CdSO₄ and Pb(NO₃)₂ solutions at different application rates. The amended soils were incubated in the greenhouse at 25 ± 4°C and 60% water-holding capacity for 12 weeks. During the incubation period, samples were collected from each pot at 0, 2, 9, and 12 weeks for enzyme assays, MBC, numeration of microbes, and DNA extraction. Fumigation-extraction method was used to measure the MBC, while plate counting techniques were used to numerate viable heterotrophic bacteria, fungi, and actinomycetes. Soil DNAs were extracted from the samples and used for DGGE analysis. Results ACP, URE, and MBC activities of microbial community were significantly lower (p < 0.05) in the metal-amended samples than those in the control. The enzyme inhibition extent was obvious between different incubation periods and varied as the incubation proceeded, and the highest rate was detected in the samples after 2 weeks. However, the lowest values of ACP and URE activities (35.6% and 36.6% of the control, respectively) were found in the Cd₃/Pb₃-treated sample after 2 weeks. Similarly, MBC was strongly decreased in both Cd/Pb-amended samples and highest reduction (52.4%) was detected for Cd₃/Pb₃ treatment. The number of bacteria and actinomycetes were significantly decreased in the heavy metal-amended samples compared to the control, while fungal cells were not significantly different (from 2.3% to 23.87%). In this study, the DGGE profile indicated that the high dose of metal amendment caused a greater change in the number of bands. DGGE banding patterns confirmed that the addition of metals had a significant impact on microbial community structure. Discussion In soil ecosystem, heavy metals exhibit toxicological effects on soil microbes which may lead to the decrease of their numbers and activities. This study demonstrated that toxicological effects of heavy metals on soil microbial community structure and activities depend largely on the type and concentration of metal and incubation time. The inhibition extent varied widely among different incubation periods for these enzymes. Furthermore, the rapid inhibition in microbial activities such as ACP, URE, and MBC were observed in the 2 weeks, which should be related to the fact that the microbes were suddenly exposed to heavy metals. The increased inhibition of soil microbial activities is likely to be related to tolerance and adaptation of the microbial community, concentration of pollutants, and mechanisms of heavy metals. The DGGE profile has shown that the structure of the bacterial community changed in amended heavy metal samples. In this research, the microbial community structure was highly affected, consistent with the lower microbial activities in different levels of heavy metals. Furthermore, a great community change in this study, particularly at a high level of contamination, was probably a result of metal toxicity and also unavailability of nutrients because no nutrients were supplied during the whole incubation period. Conclusions The added concentrations of heavy metals have changed the soil microbial community structure and activities. The highest inhibitory effects on soil microbial activities were observed at 2 weeks of incubation. The bacteria were more sensitive than actinomycetes and fungi. The DGGE profile indicated that bacterial community structure was changed in the Cd/Pb-amended samples, particularly at high concentrations. Recommendations and perspectives The investigation of soil microbial community structure and activities together could give more reliable and accurate information about the toxic effects of heavy metals on soil health.

Benzo(a)pyrene degradation was compared in soil that was either composted, incubated at a constant temperature of 22 °C, or incubated under a temperature regime typical of a composting process. After 84 days, significantly more (61%) benzo(a)pyrene was removed from composted soil compared to soils incubated at a constant temperature (29%) or at composting temperatures (46%). Molecular fingerprinting approaches indicated that in composted soils, bacterial community changes were driven by both temperature and organic amendment, while fungal community changes were primarily driven by temperature. Next-generation sequencing data revealed that the bacterial community in composted soil was dominated by Actinobacteria (order Actinomycetales), Firmicutes (class Bacilli), and Proteobacteria (classes Gammaproteobacteria and Alphaproteobacteria), regardless of whether benzo(a)pyrene was present or not. The relative abundance of unclassified Actinomycetales (Actinobacteria) was significantly higher in composted soil when degradation was occurring, indicating a potential role for these organisms in benzo(a)pyrene metabolism. This study provides baseline data for employing straw-based composting strategies for the removal of high molecular weight PAHs from soil and contributes to the knowledge of how microbial communities respond to incubation conditions and pollutant degradation.