Commercial bacterial exopolysaccharide (EPS) applications have been gaining interest; therefore, strains that provide higher yields are required for industrial-scale processes. Succinoglycan (SG) is a type of bacterial anionic exopolysaccharide produced by Rhizobium, Agrobacterium, and other soil bacterial species. SG has been widely used as a pharmaceutical, cosmetic, and food additive based on its properties as a thickener, texture enhancer, emulsifier, stabilizer, and gelling agent. An SG-overproducing mutant strain (SMC1) was developed from Sinorhizobium meliloti 1021 through N-methyl-N '-nitro-N-nitrosoguanidine (NTG) mutation, and the physicochemical and rheological properties of SMC1-SG were analyzed. SMC1 produced (22.3 g/L) 3.65-fold more SG than did the wild type. Succinoglycan (SMC1-SG) overproduced by SMC1 was structurally characterized by FT-IR and H-1 NMR spectroscopy. The molecular weights of SG and SMC1-SG were 4.20 x 10(5) and 4.80 x 10(5) Da, respectively, as determined by GPC. Based on DSC and TGA, SMC1-SG exhibited a higher endothermic peak (90.9 degrees C) than that of SG (77.2 degrees C). Storage modulus (G ') and loss modulus (G '') measurements during heating and cooling showed that SMC1-SG had improved thermal behavior compared to that of SG, with intersections at 74.9 degrees C and 72.0 degrees C, respectively. The SMC1-SG ' s viscosity reduction pattern was maintained even at high temperatures (65 degrees C). Gelation by metal cations was observed in Fe3+ and Cr3+ solutions for both SG and SMC1-SG. Antibacterial activities of SG and SMC1-SG against Escherichia coli and Staphylococcus aureus were also observed. Therefore, like SG, SMC1-SG may be a potential biomaterial for pharmaceutical, cosmetic, and food industries.

Many investigations of the preservation of soil organic carbon (SOC) in permafrost regions have examined roles of geomorphology, pedogenesis, vegetation cover, and permafrost within particular regions. However, it is difficult to disentangle the effects of multiple factors on the SOC in permafrost regions due to the heterogeneity in environmental conditions. Based on data from 73 soil study sites in permafrost regions of the eastern Qinghai-Tibetan Plateau, we developed a simple conceptual model, which relates SOC to topography, vegetation, and pedogenesis. We summarized the dominant factors and their controls on SOC using 31 measured soil physiochemical variables. Soil texture explains approximately 60% of the variations in the SOC stocks for the upper 0-2m soil. Soil particle size closely correlates to soil moisture, which is an important determinant of SOC. Soil salinity and cations are important factors as well and can explain about 10% of the variations in SOC. The SOC and total nitrogen (TN) stocks for the 1-2m depths have larger uncertainties than those of upper 1m soil layer. The vegetation, pH, and bulk density mainly affects SOC and TN stocks for the upper 1m soil layers, while the active layer thickness and soil particle size have greater influence on SOC and TN stocks for the 1-2m soils. Our results suggest that the soil particle size is the most important controller of SOC pools, and the stocks of SOC and TN are strongly effected by soil development processes in the permafrost regions of the eastern Qinghai-Tibetan Plateau. Plain Language Summary Soil organic carbon in permafrost regions is important to global warming. There are many factors that can affect soil organic carbon content in permafrost regions. How to describe the contributions of these factors to organic carbon? Are there any relationship between these factors? Here we analyzed the multiple factors which related to soil organic carbon and proposed a conceptual model to present the complex interactions between soil carbon and environmental factors. Our results showed that finer soil particles contributed the largest proportions of soil organic carbon in permafrost regions.