Production of medium chain fatty acids from antibiotic fermentation residuals pretreated by ionizing radiation: Elimination of antibiotic resistance genes.

The propagation of antibiotic resistance genes (ARGs) restricts the application of antibiotic fermentation residues (AFRs). This study investigated medium chain fatty acids (MCFA) production from AFRs, focusing on the effect of ionizing radiation pretreatment on the fates of ARGs. The results indicated that ionizing radiation pretreatment not only stimulated the MCFA production, but also inhibited the proliferation of ARGs. Radiation at 10-50 kGy decreased ARGs abundances by 0.6-21.1% at the end of fermentation process. Mobile genetic elements (MGEs) exhibited higher resistance to ionizing radiation, radiation over 30 kGy was required to suppress the proliferation of MGEs. Radiation at 50 kGy achieved an adequate inhibition to MGEs, and the degradation efficiency was 17.8-74.5% for different kinds of MGEs. This work suggested that ionizing radiation pretreatment could be a good option to ensure the safer application of AFRs by eliminating the ARGs and preventing the horizontal gene transfer of ARGs.

Production of medium chain fatty acids from fermentation of antibiotic residuals: Fate of antibiotic resistance genes.

The potential of antibiotic resistance genes (ARGs) amplification restricts the biological recovery of antibiotic fermentation residues (AFRs) through two-stage anaerobic fermentation. This study explored the fate of ARGs during the fermentation of AFRs that comprising of acidification and chain elongation (CE). Results showed that with the alteration of fermentation process from acidification to CE, microbial richness was significantly increased, total abundance of ARGs was slightly decreased by 1.84%, and the significant negative correlations between ARGs and microbes were increased, implied the inhibitory effect of CE microbes to ARGs amplification. However, the total abundance of mobile genetic elements (MGEs) was increased by 24.5%, indicating that the potential of gene horizontal transfer of ARGs increased. This work suggested that two-stage anaerobic fermentation could effectively restrict the ARGs amplification, but more concerns are needed for the long-term dissemination of ARGs.

Inhibitory effect of acetic acid on dark-fermentative hydrogen production.

This study examined the working mechanisms of acetic acid inhibition on dark fermentative hydrogen production. It was found that undissociated acetic acid (UAA) concentration was the critical factor in acetic acid inhibition. Hydrogen production activity decreased by 50 % and 90 % when UAA concentrations was 76.3 mg/L (1.27 mmol/L) and 686.7 mg/L (11.44 mmol/L), respectively. Dominant microbes were changed from genus Clostridium_sensu_stricto_1 to genus Inhella, Aquabacterium and Caulobacter under the stress of acetic acid inhibition. Functional enzyme analysis showed that acetic acid inhibited the hydrogen production by activating the lactate formation pathway when UAA concentration was below the inhibition threshold, while by impairing most hydrogen-producing pathways when UAA concentration was over the inhibition threshold. In brief, acetic acid inhibited the hydrogen production by altering the dominant microbial community and regulating the metabolic pathways, controlling the UAA concentration would be a good strategy to alleviate the acetic acid inhibition.

Using geographical semi-variogram method to quantify the difference between NO2 and PM2.5 spatial distribution characteristics in urban areas.

Urban air pollutant distribution is a concern in environmental and health studies. Particularly, the spatial distribution of NO2 and PM2.5, which represent photochemical smog and haze pollution in urban areas, is of concern. This paper presents a study quantifying the seasonal differences between urban NO2 and PM2.5 distributions in Foshan, China. A geographical semi-variogram analysis was conducted to delineate the spatial variation in daily NO2 and PM2.5 concentrations. The data were collected from 38 sites in the government-operated monitoring network. The results showed that the total spatial variance of NO2 is 38.5% higher than that of PM2.5. The random spatial variance of NO2 was 1.6 times than that of PM2.5. The nugget effect (i.e., random to total spatial variance ratio) values of NO2 and PM2.5 were 29.7 and 20.9%, respectively. This indicates that urban NO2 distribution was affected by both local and regional influencing factors, while urban PM2.5 distribution was dominated by regional influencing factors. NO2 had a larger seasonally averaged spatial autocorrelation distance (48km) than that of PM2.5 (33km). The spatial range of NO2 autocorrelation was larger in winter than the other seasons, and PM2.5 has a smaller range of spatial autocorrelation in winter than the other seasons. Overall, the geographical semi-variogram analysis is a very effective method to enrich the understanding of NO2 and PM2.5 distributions. It can provide scientific evidences for the buffering radius selection of spatial predictors for land use regression models. It will also be beneficial for developing the targeted policies and measures to reduce NO2 and PM2.5 pollution levels.