Genome sequence of the anaerobic bacterium Bacillus sp. strain ZYK, a selenite and nitrate reducer from paddy soil.

Bacillus sp. strain ZYK, a member of the phylum Firmicutes, is of interest for its ability to reduce nitrate and selenite and for its resistance to arsenic under anaerobic conditions. Here we describe some key features of this organism, together with the complete genome sequence and annotation. The 3,575,797 bp long chromosome with its 3,454 protein-coding and 70 RNA genes, and the information gained from its sequence will be relevant to the elucidation of microbially-mediated transformations of nitrogen, selenium and arsenic in paddy soil.

Dechlorination of p,p'-DDTs coupled with sulfate reduction by novel sulfate-reducing bacterium Clostridium sp. BXM.

A novel non-dsrAB (without dissimilatory sulfite reductase genes) sulfate-reducing bacterium (SRB) Clostridium sp. BXM was isolated from a paddy soil. Incubation experiments were then performed to investigate the formation of reduced sulfur compounds (RSC) by Clostridium sp. BXM, and RSC-induced dechlorination of p,p'-DDT in culture medium and soil solution. The RSCs produced were 5.8 mM and 4.5 mM in 28 mM sulfate amended medium and soil solution respectively after 28-day cultivation. The p,p'-DDT dechlorination ratios were 74% and 45.8% for 5.8mM and 4.5 mM RSCs respectively at 6h. The metabolites of p,p'-DDT found in the two reaction systems were identified as p,p'-DDD and p,p'-DDE. The dechlorination pathways of p,p'-DDT to p,p'-DDD and p,p'-DDE were proposed, based on mass balance and dechlorination time-courses. The results indicated that RSC-induced natural dechlorination may play an important role in the fate of organochlorines.

Excessive sulfur supply reduces cadmium accumulation in brown rice (Oryza sativa L.).

Human activities have resulted in cadmium (Cd) and sulfur (S) accumulation in paddy soils in parts of southern China. A combined soil-sand pot experiment was conducted to investigate the influence of excessive S supply on iron plaque formation and Cd accumulation in rice plants, using two Cd levels (0, 1.5 mg kg(-1)) combined with three S concentrations (0, 60, 120 mg kg(-1)). The results showed that excessive S supply significantly decreased Cd accumulation in brown rice due to the decrease of Cd availability and the increase of glutathione in rice leaves. But excessive S supply obviously increased Cd accumulation in roots due to the decrease of iron plaque formation on the root surface of rice. Therefore, excessive S supply may result in loss of rice yield, but it could effectively reduce Cd accumulation in brown rice exposed to Cd contaminated soils.

Atmospheric inorganic nitrogen deposition to a typical red soil forestland in southeastern China.

A 2-year monitoring study was conducted to estimate nitrogen deposition to a typical red soil forestland in southeastern China. The dry deposition velocities (V(d)) were estimated using big leaf resistance analogy model. Atmospheric nitrogen dry deposition was estimated by combing V(d) and nitrogen compounds concentrations, and the wet deposition was calculated via rainfall and nitrogen concentrations in rainwater. The total inorganic nitrogen deposition was 83.7 kg ha(-1) a(-1) in 2004 and 81.3 kg ha(-1) a(-1) in 2005, respectively. The dry deposition contributed 78.6% to total nitrogen deposition, in which ammonia was the predominant contributor that accounted for 86.1%. Reduced nitrogen compounds were the predominant contributors, accounting for 78.3% of total nitrogen deposition. The results suggested that atmospheric inorganic nitrogen could be attributed to intensive agricultural practices such as excessive nitrogen fertilization and livestock production. Therefore, impacts of atmospheric nitrogen originated from agriculture practices on nearby forest ecosystems should be evaluated.

Sulfur (S)-induced enhancement of iron plaque formation in the rhizosphere reduces arsenic accumulation in rice (Oryza sativa L.) seedlings.

The effects of two sulfur (S) sources (SO(4)(2-), S(0)), and three rates of S application (0, 30, 120 mgS/kg) on the formation of iron plaque in the rhizosphere, and on the root surface of rice, and As (arsenic) uptake into rice (Oryza sativa L.) were studied in a combined soil-sand culture experiment. Significant differences in As uptake into rice between +S and -S treatments were observed in relation to S sources, and rates of S application. Concentrations of As in rice shoots decreased with increasing rates of S application. The mechanism could be ascribed to sulfur, induced the formation of iron plaque, since concentrations of Fe in iron plaque on quartz sands in the rhizosphere, and on the root surface of rice increased with increasing rates of S application. The results suggest that sulfur fertilization may be important for the development approaches to reducing As accumulation in rice.

[Distribution characteristics and sources identification of PAHs in ancient paddy soil].

Soil samples of current paddy soils, ancient paddy soil/ancient dry land soil, and bottom soils were collected from two sites in Chuodunshan Site of Majiabang Culture (about 6,000a). 15 polycyclic aromatic hydrocarbons (PAHs) were analyzed with HPLC, and their possible sources were identified. The sum of 15 PAHs was 202.9microg x kg(-1) and 207.7microg x kg(-1) in the surface soils from Site A and Site B respectively, which were mainly deposited from atmosphere. In ancient paddy soil from Site A, the total PAHs concentration sharply decreased to 56.0microg x kg(-1), but was still higher than those in ancient dry land soil and bottom soils with the sum of 32.0 approximately 36.9microg x kg(-1). In ancient paddy soil, the concentrations of 2-ring and 3-ring PAHs took a larger portion of 63 percents to the total PAHs, and naphthalene and phenanthrene were the most abundant compounds, while PAHs of more than 4 rings took a small part. The ratios of phenanthrene anthracene and benzo(a) anthracene chrysene and 13C-NMR spectrum of soil organic matter showed that PAHs in ancient paddy soil mainly originated from rice straw burning, biogenesis under reducing conditions may be another source.