Biochar has been suggested to improve acidic soils and to mitigate greenhouse gas emissions. However, little has been done on the role of biochar in ameliorating acidified soils induced by overuse of nitrogen fertilizers. In this study, we designed a pot trial with an acidic soil (pH 4.48) in a greenhouse to study the interconnections between microbial community, soil chemical property changes, and N2O emissions after biochar application. The results showed that biochar increased plant growth, soil pH, total carbon, total nitrogen, C/N ratio, and soil cation exchange capacity. The results of high-throughput sequencing showed that biochar application increased α-diversity significantly and changed the relative abundances of some microbes that are related with carbon and nitrogen cycling at the family level. Biochar amendment stimulated both nitrification and denitrification processes, while reducing N2O emissions overall. Results of redundancy analysis indicated biochar could shift the soil microbial community by changing soil chemical properties, which modulate N-cycling processes and soil N2O emissions. The significantly increased nosZ transcription suggests that biochar decreased soil N2O emissions by enhancing its further reduction to N2.

Biochar Impacts Soil Microbial Community Composition and Nitrogen Cycling in an Acidic Soil Planted with Rape

Bacterial exopolysaccharides (EPS) are products of biotechnology that are of high interest due to their rheological properties. This is the case of sphingans, a group of structurally related EPS secreted by members of the genus Sphingomonas. Among these, gellan is a multifunctional gelling agent produced in high yields by the non-pathogenic strain Sphingomonas elodea ATCC 31461. In its native form, gellan is a linear anionic EPS based on a tetrasaccharide repeat unit composed of two molecules of d-glucose, one of l-rhamnose and one of d-glucuronic acid. The native gellan is partially esterified with acyl substituents (1 mol of glycerate and 0.5 mol of acetate) per repeat unit. Gellan has unique characteristics and has many applications, particularly in the food, pharmaceutical, and biomedical fields. This review summarizes current knowledge on the structure and properties of gellan and provides details about the biosynthesis of this exopolysaccharide. In addition, a highlight of the importance of gellan in industrial and medicinal applications is given.

Occurrence, production, and applications of gellan: current state and perspectives

Because soil is expected to be a major sink for engineered nanoparticles (ENPs) released to the environment, the effects of ENPs on soil processes and the organisms that carry them out should be understood. DNA-basedfingerprinting analyses have shown that ENPs alter soil bacterial communities, but specific taxon changes remain unknown. We used bar-coded pyrosequencing to explore the responses of diverse bacterial taxa to two widely used ENPs, nano-TiO2and nano-ZnO, at various doses (0, 0.5, 1.0, and 2.0 mg g 1 soil for TiO2; 0.05, 0.1, and 0.5 mg g 1 soil for ZnO) in incubated soil microcosms. These ENPs significantly altered the bacterial communities in a dose-dependent manner, with some taxa increasing as a proportion of the community, but more taxa decreasing, indicating that effects mostly reduced diversity. Some of the declining taxa are known to be associated with nitrogenfixation (Rhizobiales,Bradyrhizobiaceae, andBradyrhizobium) and methane oxidation (Methylobacteriaceae), while some positively impacted taxa are known to be associated with the decomposition of recalcitrant organic pollutants (Sphingomonadaceae) and biopolymers including protein (Streptomycetaceae andStreptomyces), indicating potential consequences to ecosystem-scale processes. The latter was suggested by a positive correlation between protease activity and the relative abundance ofStreptomycetaceae (R0.49,P0.000) andStreptomyces(R0.47,P0.000). Our results demonstrate that some metal oxide nanoparticles could affect soil bacterial communities and associated processes through effects on susceptible, narrow-function bacterial taxa.

Identification of soil bacteria susceptible to TiO2 and ZnO nanoparticles.

Summary The microbial exopolysaccharides are water-soluble polymers secreted by microorganisms during fermentation. The biopolymer gellan gum is a relatively recent addition to the family of microbial polysaccharides that is gaining much importance in food, pharmaceutical and chemical industries due to its novel properties. It is commercially produced by C. P. Kelco in Japan and the USA. Further research and development in biopolymer technology is expected to expand its use. This article presents a critical review of the available information on the gellan gum synthesized by Sphingomonas paucimobilis with special emphasis on its fermentative production and downstream processing. Rheological behaviour of fermentation broth during fermentative production of gellan gum and problems associated with mass transfer have been addressed. Information on the biosynthetic pathway of gellan gum, enzymes and precursors involved in gellan gum production and application of metabolic engineering for enhancement of yield of gellan gum has been specified. Characteristics of gellan gum with respect to its structure, physicochemical properties, rheology of its solutions and gel formation behaviour are discussed. An attempt has also been made to review the current and potential applications of gellan gum in food, pharmaceutical and other industries.

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Gellan Gum: Fermentative Production, Downstream Processing and Applications

We investigated the effects of wastewater treatment plant (WWTP) discharge on the ecology of bacterial communities in the sediment of a small, low-gradient stream in South Australia The quantification of genes involved in the biogeochemical cycling of carbon and nitrogen was used to assess potential impacts on ecosystem functions The effects of disturbance on bacterial community structure were assessed by PCR-denaturing gradient gel electrophoresis of 16S rRNA genes, and clone library analysis was used to phylogenetically characterize significant shifts Significant (P < 005) shifts in bacterial community structures were associated with alteration of the sediment's physicochemical properties, particularly nutrient loading from the WWTP discharge The effects were greatest at the sampling location 400 m downstream of the outfall where the stream flow is reduced This highly affected stretch of sediment contained representatives of the gammaproteobacteria that were absent from less-disturbed sites, including Oceanospirillales and Methylococcaceae 16S rRNA gene sequences from less-disturbed sites had representatives of the Caulobacteraceae, Sphingomonadaceae, and Nitrospirae which were not represented in samples from disturbed sediment The diversity was lowest at the reference site; it increased with proximity to the WWTP outfall and declined toward highly disturbed (400 m downstream) sites (P < 005) The potential for biological transformations of N varied significantly with the stream sediment location (P < 005) The abundance of amoA, narG, and nifH genes increased with the distance downstream of the outfall These processes are driven by N and C availability, as well as redox conditions Together these data suggest cause and effect between nutrient loading into the creek, shift in bacterial communities through habitat change, and alteration of capacity for biogeochemical cycling of N

Effect of Wastewater Treatment Plant Effluent on Microbial Function and Community Structure in the Sediment of a Freshwater Stream with Variable Seasonal Flow

David B Ringelberg

Papers

The genus Sphingomonas: physiology and ecology.