Genome-centric metagenomics provides new insights into metabolic pathways of polyhydroxyalkanoates biosynthesis and functional microorganisms subsisting on municipal organic wastes.

The microbial community of a sequencing batch reactor operated under feast and famine conditions for production of polyhydroxyalkanoates (PHAs) was characterized through high-throughput sequencing and metagenomic analysis. The fermented food waste and chemically-enhanced primary sludge was fed in this bioreactor. After acclimation, the PHA yield achieved as high as 0.60-0.69 g CODPHA/g CODS. The complete changes of microbial community structure were found during shifts of feedstock. A synthesis of SCL/MCL-PHAs pathway was established for PHA-producing bioreactor in this mixed-culture system. The structure-performance relationship of PHA-producing microbial community and feedstock composition was investigated. The results showed that microbial community tends to be decentralized and prefer team work for PHA synthesis to consume the multiple substrates and digest inevitable non-VFA contents in fermented liquor. This study also discovered unreported potential PHA producers (e.g., genera Tabrizicola, Nannocystis, Ga0077539, Ga0077559, JOSHI-001, SNC69-320 and UBA2334) subsisting on municipal organic wastes and expands the current knowledge about mixed-culture system that the PHA synthesis pathway is widely existed in activated sludge.

[Effects of Arbuscular Mycorrhizal Fungi on the Growth of Reeds in Wetland Soils with Different Salt Content].

A greenhouse pot experiment was conducted to investigate the effects of arbuscular mycorrhizal (AM) fungi Claroideoglomus etunicatum (CE), Rhizophagus intraradices (RI), Funneliformis mosseae (FM) and Glomus versiforme (GV) on AM colonization rate, biomass, mineral nutrient uptake, C: N: P ratios and Na and Cl- concentrations of reeds (Phragmites australis) grown in saline and non-saline wetland soils. The aim was to provide a technical basis for the ecological revegetation and salinity restoration of wetland ecosystem. The results indicated that symbiotic associations were successfully established between the four isolates and reeds grown in the two types of wetland soils. The average AM colonization rates ranged from 2.5% to 38%. The mean root colonization rate of CE was significantly higher than those of the other three isolates. There were no significant differences in root colonization rates between saline and non-saline wetland soils. The biomass and nutrient contents of reeds grown in non-saline wetland soils were significantly higher than those grown in saline wetland soils. However, Na+ and Cl- concentrations of reeds grown in non-saline wetland soils were significantly lower than those grown in saline wetland soils. In non-saline wetland soils, inoculation with GV significantly increased the shoot dry weight and the shoot N, P, K, Ca and Mg contents of reeds. Inoculation with GV and RI significantly improved the root P and K contents of reeds. Inoculation with the four AM fungi significantly reduced the shoot N: P ratios. Inoculation with FM and GV significantly reduced the root C : N and C : P ratios. Inoculation with the four AM fungi significantly reduced the shoot Cl- concentrations. Inoculation with RI significantly reduced the shoot Na+ concentrations. In saline wetland soils, inoculation with AM fungi had no significant effect on the biomass, mineral nutrient uptake and Na+ and Cl- concentrations of reeds. The results demonstrated that the four AM fungi isolates had different effects on the growth of reeds in wetland soils with different salt contents. Inoculation with AM fungi played a more positive role in improving the growth of reeds in non-saline wetland soil than those in saline wetland soil. Further experiments should be conducted to screen optimal AM fungi isolates under field conditions and to evaluate the practical effects of AM fungi on the growth of reeds in wetland soils with different salt contents.

[Distribution characteristic and current situation of soil rare earth contamination in the Bayan Obo mining area and Baotou tailing reservoir in Inner Mongolia].

The pollution status and distribution characteristic of rare earth elements in soil were analyzed around Bayan Obo mining area and Baotou tailing reservoir located in Inner Mongolia grassland ecosystem, aiming at grasping the overall situation of grassland ecosystem pollution caused by rare earth elements and providing basic information as well as theoretical basis. The results indicated that seven rare earth elements in soils from different directions of Baotou tailing reservoir accumulated to a certain extent compared to the soil background value of Inner Mongolia. The pollution degree was Ce > La > Nd > Pr > Sm > Y > Eu. Within 50 m from the edge of tailing reservoir, soil rare earth contamination was the most serious, with the concentrations of La, Ce, Pr, Nd, Sm, Eu and Y reaching 11,45.0 mg x kg(-1), 23,636.0 mg x kg(-1), 4568.16 mg x kg(-1) , 6855.51 mg x kg(-1), 582.18 mg x kg(-1), 94.21 mg x kg(-1)), and 136.25 mg x kg(-1), respectively. Owing to the dominant wind direction of northwest, soils from the southeast were contaminated most seriously. For Bayan Obo mining area, the concentrations of seven rare earth elements in soil from the mining area were significantly higher than those of other areas investigated, with the concentrations of La, Ce, Pr, Nd, Sm, Eu and Y reaching 3112.56 mg x kg(-1), 7142.12 mg x kg(-1), 1467.12 mg x kg(-1), 2552.80 mg x kg(-1), 210.80 mg x kg(-1), 36.20 mg x kg(-1) and 63.22 mg x kg(-1), respectively. The soils of six areas of Bayan Obo mining area were all contaminated by rare earth elements, and the contamination degree was in the order of mining area > outside the dump > east side of the railway > the dump > outside the urban area > west side of the railway. Besides, the transportation of rare earth ore led to the soil rare earth contamination along the railway, and the distribution characteristic of rare earth elements in soils along the railway was affected by the dominant wind direction of northwest. Baotou tailing reservoir and Bayan Obo mining area had the same contamination characteristic, and the concentrations of rare earth elements were in accordance with those in the tailings. The health and stabilization of local grassland ecosystem are being threatened by excessive soil rare earth elements.

[Effects of arbuscular mycorrhizal fungi on the growth and rare earth elements uptake of soybean grown in rare earth mine tailings].

A greenhouse pot experiment was conducted to investigate the influence of arbuscular mycorrhizal (AM) fungi Glomus versiforme on the plant growth, nutrient uptake, C: N: P stoichiometric, uptake of heavy metals and rare earth elements by soybean (Glycine max) grown in rare earth mine tailings. The aim was to provide a basis for the revegetation of rare earth mine tailings. The results indicated that soybean had a high mycorrhizal colonization and symbiotic associations were successfully established with G. versiforme, with an average rate of approximately 67%. The colonization of G. versiforme significantly promoted the growth of soybean, increased P, K contents, and decreased C: N: P ratios, supporting the growth rate hypothesis. Inoculation with G. versiforme significantly decreased shoots and roots La, Ce, Pr and Nd concentrations of soybean compared to the control treatment. However, inoculation with G. versiforme had no significant effect on the heavy metal concentrations, except for significantly decreased shoot Fe and Cr concentrations and increased root Cd concentrations. The experiment demonstrates that AM fungi have a potential role for soybean to adapt the composite adversity of rare earth tailings and play a positive role in revegetation of rare earth mine tailings. Further studies on the role of AM fungi under natural conditions should be conducted.

[Characteristic and evaluation of soil pollution by heavy metal in different functional zones of Hohhot].

The residential areas, cultural and educational areas, city parks, commercial areas, urban roads, industrial zones, and development zones in Hohhot were selected as the research objects. Sixty-two soil samples were collected by triple subsampling technique in the seven functional zones. The aim of this study is to control the soil heavy metal pollution of Hohhot and provide the basic information. To investigate and analyze the heavy metal pollution in soil in different functional zones of Hohhot, the pollution of heavy metal was assessed with single factor pollution index and Nemerow integrated pollution index, and the pollution sources were discriminated by Principal Component Analysis. Contents of seven kinds of heavy metals were analyzed in different functional zones of Hohhot. The mean contents of heavy metals in soil samples exceeded the corresponding background values in the Inner Mongolia Autonomous Region. The mean contents of Cu and Zn were 2. 33 and 1. 85 times, respectively, as high as the soil background values of the Inner Mongolia Autonomous Region. Single factor pollution index showed that the urban soil in Hohhot has been polluted by heavy metals. The Cu pollution was the most severe in commercial areas, and the pollution degree was in the following order: Cu > Zn > Cr > Mn > As > Ni > Pb. Nemerow integrated pollution index showed that soils from the commercial areas were seriously contaminated by heavy metals. The soil of urban roads was moderately polluted. The soils from cultural and educational areas and the city parks were slightly polluted. The Nemerow integrated pollution index of the seven areas ranked as follows: commercial areas (3.03) > urban roads (2.12) > residential areas (1.98) > cultural and educational areas (1.81) > industrial zones (1.72) > development zones (1.36) > city parks (1. 28). The results of Principal Component Analysis showed that the heavy metals in soil of Hohhot came from different sources. Cr, Cu, Mn, Pb and Zn were mainly originated from anthropogenic sources while Ni and As were mainly controlled by natural sources. The healthy development of urban ecosystem has been threatened by soil heavy metal pollution in Hohhot.

[Effects of arbuscular mycorrhizal fungi on the vegetation restoration of different types of coal mine spoil banks].

A greenhouse pot experiment was conducted to investigate the influence of arbuscular mycorrhizal (AM) fungi Glomus etunicatum (GE) and Glomus versiforme (GV) on the plant growth, nutrient uptake, C: N: P stoichiometric, uptake of heavy metals by maize (Zea mays L.) grown in three types of coal mine spoil banks. The aim was to provide a technical basis for the revegetation of coal mine spoil banks in grassland ecosystem. The results indicated that the symbiotic associations were successfully established between two isolates and maize grown in the three substrates, with an average mycorrhizal colonization rate ranging from 36% to 54%. The colonization of two AM fungi significantly increased the dry weight of maize grown in recent discharged and weathered coal mine spoils and GE increased those grown in weathered coal mine spoil. Inoculation with AM fungi promoted the uptake of N, P and K by maize to varying degrees. In addition, inoculation with GE and GV also decreased C: N: P ratios, supporting the growth rate hypothesis, and had significantly differences on concentrations of Cu, Fe, Mn and Zn in shoots and roots of maize. The results indicated that GE and GV had different mycorrhizal effects on maize in the three types of substrates. GV was more suitable for the revegetation of recent discharged coal mine spoil and weathered coal mine spoil, while GE was more suitable for the revegetation of spontaneous combusted coal mine spoil. The experiment demonstrates that AM fungi have a potential role for maize to enhance the ability to adapt the composite adversity of different types of coal mine spoil and play a positive role in the revegetation of different coal mine spoil banks. Further field experiments should be conducted to evaluate the practical effects of AM fungi on the vegetation restoration of different types of coal mine spoil under field conditions.

[Distribution characteristic and assessment of soil heavy metal pollution in the iron mining of Baotou in Inner Mongolia].

The pollution status and total concentration of soil heavy metals were analyzed around tailing reservoir of Baotou and iron mining of Bayan Obo located in Inner Mongolia grassland ecosystem. Aim of the study is to control soil heavy metal pollution of grassland mining area and provide the basic information. The results indicated that the soils from different directions of the tailing reservoir were contaminated by Pb, Cu, Zn and Mn. According to the single factor pollution index, the pollution degree was Mn > Zn > Pb > Cu. According to Nemerow integrated pollution index, the indexes of the northeast, southeast, southwest, and northwest of the tailing reservoir, were 2.43, 10.2, 1.88, 1.64. Soils from the southeast had the most serious heavy metal contamination because of the dominant wind of northwest. Within 50 m from the edge of tailing reservoir, heavy metal contamination was most serious except Cu. With regard to Bayan Obo iron mining, the single factor pollution index indicated that the soils from the six surveyed regions were contaminated by Pb, Cu, Zn and Mn. The integrated pollution index indicated that the indexes of the six regions, such as the mining area, the dump, outside the dump, outside the urban area, east region of the railway, and west region of the railway, were 14.3, 4.30, 2.69, 3.41, 2.88, and 2.20, respectively. The soil pollution degree of the mining area was the highest. Additionally, the transport of ore resulted in soil heavy metal pollution along railway. In general, soils of the two studied areas had the similar pollution characteristic, and the elements of heavy metal contamination were corresponding with the concentrations of tailings. The health and stabilization of grassland ecosystem are being threatened by soil heavy metals.