Enhanced Stability and Detection Range of Microbial Electrochemical Biotoxicity Sensor by Polydopamine Encapsulation.

With the rapid development of modern industry, it is urgently needed to measure the biotoxicity of complex chemicals. Microbial electrochemical biotoxicity sensors are an attractive technology; however, their application is usually limited by their stability and reusability after measurements. Here, we improve their performance by encapsulating the electroactive biofilm with polydopamine (PDA), and we evaluate the improvement by different concentrations of heavy metal ions (Cu2+, Ag+, and Fe3+) in terms of inhibition ratio (IR) and durability. Results indicate that the PDA-encapsulated sensor exhibits a more significant detection concentration than the control group, with a 3-fold increase for Cu2+ and a 1.5-fold increase for Ag+. Moreover, it achieves 15 more continuous toxicity tests than the control group, maintaining high electrochemical activity even after continuous toxicity impacts. Images from a confocal laser scanning microscope reveal that the PDA encapsulation protects the activity of the electroactive biofilm. The study, thus, demonstrates that PDA encapsulation is efficacious in improving the performance of microbial electrochemical biotoxicity sensors, which can extend its application to more complex media.

[Dynamics of microbes and enzyme activities during litter decomposition of Pinus massoniana forest in mid-subtropical area].

The dynamics of microbial quantity and enzyme activities during decomposition process of masson pine (Pinus massoniana) leaf litter, oak (Quercus aliena) leaf litter and their mixture (at natural mass ratio, 8: 2) were studied with litterbag method in the pinus forest typical vegetations of mid-subtropical Jinyun Mountain nature reserve. The results showed that the decomposition constant K of leaf litter ranked as follows: mixture (0.94) > oak (0.86) > masson pine (0.67). Microbial groups and enzyme activity exhibited some similar responses to the litter decomposition process. After 135 days, fungal and microbial quantities reached the maximum while bacterial and actinomycetic number reached the minimum, presumably due to the high-temperature environment. The correlative analysis showed that the cellulase and acid phosphatase activity had significant positive relationship with the dry weight remaining rate (P < 0.05), which played a key role for microbes in utilizing the substrates at early stages. Meanwhile, the polyphenol oxidase activity showed highly significant negative correlation with the dry weight remaining rate (P < 0.01) in pine litter and the mixed litter, which worked on further decay of recalcitrant compound at late stages. Through the whole process, the microbial quantity and polyphenol oxidase activity were generally in the order of oak litter > mixed litter > pine litter, while in most cases the oak litter showed the lowest acid phosphatase activity, the ranking of which had some differences with the order of the decomposition constant K, indicating that litter decomposition was the result of integrated action by microbe and many kinds of enzymes. The results suggested that differences in litter composition and seasonal climate strongly influenced the microbial communities and the ecosystem processes they mediate. When mixed with oak leaves in given stand, the pine litter had an accelerating decomposition rate, which might depend on the higher microbial quantity and polyphenol oxidase activity in the mixed litter.