With the emergence of antibiotic-resistant strains of bacteria, the available options for treating bacterial infections have become very limited, and the search for a novel general antibacterial therapy has received much greater attention. Quorum quenching can be used to control disease in a quorum sensing system by triggering the pathogenic phenotype. The interference with the quorum sensing system by the quorum quenching enzyme is a potential strategy for replacing traditional antibiotics because the quorum quenching strategy does not aim to kill the pathogen or limit cell growth but to shut down the expression of the pathogenic gene. Quorum quenching enzymes have been identified in quorum sensing and non-quorum sensing microbes, including lactonase, acylase, oxidoreductase and paraoxonase. Lactonase is widely conserved in a range of bacterial species and has variable substrate spectra. The existence of quorum quenching enzymes in the quorum sensing microbes can attenuate their quorum sensing, leading to blocking unnecessary gene expression and pathogenic phenotypes. In this review, we discuss the physiological function of quorum quenching enzymes in bacterial infection and elucidate the enzymatic protection in quorum sensing systems for host diseases and their application in resistance against microbial diseases.

Biochar can enhance soil fertility to increase agricultural productivity, whereas its improvement in soil microbial activity is still unclear. In this article, the influence of biochar on the cell growth and the potassium-solubilizing activity of Bacillus mucilaginosus AS1153 was examined. The impact on cell growth is related to the biochar-derived feedstocks and the particle size of biochar. Both intrinsic features and inner component fraction can promote the cell growth of B. mucilaginosus AS1153. The potassium-solubilizing activity was increased by 80% when B. mucilaginosus was incubated in conjunction with the biochar derived from corn stover. The survival time of B. mucilaginosus also was prolonged by adsorption in biochar. The experimental results suggested that the biochar containing B. mucilaginosus could be used as a potential biofertilizer to sustain crop production.

Rice blast caused by Magnaporthe grisea is considered to be one of the most devastating diseases in most rice-growing regions. In order to search for an effective agent to protect against rice infection, the elicitor activity of algino-oligosaccharides was evaluated in germinating rice, in which accumulation of oryzalexin C could be detected sensitively. The maximal elicitor activity was detected in germinating rice seedlings when the fractions of alginate degradation products with a degree of polymerization of 7.9 (S3) and 6.5 (S4) were used as elicitors. Algino-oligosaccharides could induce the enzyme activities of phenylalanine ammonia lyase, peroxidase and catalase in rice plant cells for protection of the plant against the invading pathogen. With utilization of algino-oligosaccharides, the disease index caused by Magnaporthe grisea could be reduced from 17.74% to 10.81% and the protection efficacy was 39.06%. These findings suggest that algino-oligosaccharides could be applied as a biological agent to control rice blast disease.