Oxygen tolerance capacity of upflow anaerobic solid-state(UASS) with anaerobic filter(AF) system

In order to investigate the oxygen tolerance capacity of upflow anaerobic solid-state（UASS）with anaerobic filter（AF） system, the effect of microaeration on thermophilic anaerobic digestion of maize straw was investigated under batch conditions and in the UASS with AF system. Aeration intensities of 0–431 m L O2/gvswere conducted as pretreatment under batch conditions. Aeration pretreatment obviously enhanced anaerobic digestion and an aeration intensity of 431 m L O2/gvsincreased the methane yield by 82.2%. Aeration intensities of 0–355 m L O2/gvswere conducted in the process liquor circulation of the UASS with AF system. Dissolved oxygen（DO） of UASS and AF reactors kept around 1.39 ±0.27 and 0.99 ± 0.38 mg/L, respectively. p H was relatively stable around 7.11 ± 0.04. Volatile fatty acids and soluble chemical oxygen demand concentration in UASS reactor were higher than those in AF reactor. Methane yield of the whole system was almost stable at 85 ± 7 m L/gvs as aeration intensity increased step by step. The UASS with AF system showed good oxygen tolerance capacity.

Divergent responses of growth rate and antioxidative system of ten Bacillus strains to acid stresses

Response of growth rate and antioxidative system of ten Bacillus strains to acid stresses was assayed.Strong acid treatment significantly decreased the growth rate of the strains.Acid stresses increased the GPX activity and GSSG content of the tested strains.Divergent changes occurred in ROS and antioxidative system(SOD,CAT,GR,MDA and GSH).Environmental changes including soil acidification exert obvi-ous stresses on soil ecosystems and influence soil microor-ganisms.In this study,ten microbial strains were incubated under different acid treatments to investigate responses of microbial growth and antioxidative system to acid stress.All the strains belong to Bacillus genus,but exhibit distinct ecological functions.We observed that these microbial strains had obviously different pH tolerance threshold,in spite of the close phylogenetic classification among strains.Acid stresses exerted significant effects on microbial antiox-idative system,including superoxide dismutase(SOD),cata-lase(CAT)and glutathione transferring enzymes(GPX and GR)and reactants(GSH and GSSH),but the effects were strain specific.Furthermore,we found acid stress effects on total variances of the investigated microbial antioxidative system along the first two principal components(PCs).Activities of CAT and SOD contributed substantially to PC1 that reflected obvious acid effects on NC7 and ZC4,and closely related to intracellular malondialdehyde content.The GSSG activities and GSH/GSSG contributed greatly to PC2 that unveiled acid stress effects on most of the microbial strains.Our results highlight substantially heterogeneous responses of microbial strains to acid stress and support that phylogenetic closeness does not imply functional similarity of soil microorganisms under environmental changes.