Microbial biodegradation is one of the acceptable technologies to remediate and control the pollution by polycyclic aromatic hydrocarbon (PAH). Several bacteria, fungi, and cyanobacteria strains have been isolated and used for bioremediation purpose. This review paper is intended to provide key information on the various steps and actors involved in the bacterial and fungal aerobic and anaerobic degradation of pyrene, a high molecular weight PAH, including catabolic genes and enzymes, in order to expand our understanding on pyrene degradation. The aerobic degradation pathway by Mycobacterium vanbaalenii PRY-1 and Mycobactetrium sp. KMS and the anaerobic one, by the facultative bacteria anaerobe Pseudomonas sp. JP1 and Klebsiella sp. LZ6 are reviewed and presented, to describe the complete and integrated degradation mechanism pathway of pyrene. The different microbial strains with the ability to degrade pyrene are listed, and the degradation of pyrene by consortium is also discussed. The future studies on the anaerobic degradation of pyrene would be a great initiative to understand and address the degradation mechanism pathway, since, although some strains are identified to degrade pyrene in reduced or total absence of oxygen, the degradation pathway of more than 90% remains unclear and incomplete. Additionally, the present review recommends the use of the combination of various strains of anaerobic fungi and a fungi consortium and anaerobic bacteria to achieve maximum efficiency of the pyrene biodegradation mechanism.

To explore the effect of low-temperature and low-salt fermentation on the volatile flavor substances of Chinese kohlrabi, low-temperature and low-salt fermented Chinese kohlrabi (LSCK) and traditional high-salt fermented Chinese kohlrabi (HSCK) were produced. The physicochemical and texture properties of the two kinds of Chinese kohlrabies were evaluated. Headspace gas chromatography-ion mobility spectrometry (GC-IMS) and electronic nose (E-nose) were used to analyze the volatile flavor substances of the kohlrabi. The results showed that the total acid content significantly decreased (p < 0.05), while protein and reducing sugar contents significantly increased (p < 0.05) by low-temperature and low-salt fermentation. A total of 114 volatile flavor substances were identified. The alcohol, ketone, pyrazine, ether, and nitrile contents in LSCK were significantly higher than those in HSCK (p < 0.05). Moreover, the unpleasant flavor from the 3-methylbutyric acid formation was effectively depressed in LSCK. The principal component analysis (PCA) and orthogonal partial least squares discrimination analysis (OPLS-DA) models established by multivariate statistical analysis significantly distinguished the two types of kohlrabies. Multivariate statistical analysis suggested that 16 volatile flavor substances with VIP >1, including tetrahydrothiophene, ethyl 3-(methylthio)propanoate, 3-methylbutyric acid, hexanenitrile, and 3-methyl-3-buten-1-ol, could be used as potential biomarkers for identifying LSCK and HSCK. The E-nose analysis further demonstrated that there was a significant difference in overall flavor between the LSCK and HSCK. The present study provides support for the development of green processing technology and new low-salt Chinese kohlrabi products.

Rhodococcus sp. P14 was isolated from crude-oil-contaminated sediments, and a wide range of polycyclic aromatic hydrocarbons (PAHs) could be used as the sole source of carbon and energy. A key CYP450 gene, designated as cyp108j1 and involved in the degradation of PAHs, was identified and was able to hydroxylate various PAHs. However, the regulatory mechanism of the expression of cyp108j1 remains unknown. In this study, we found that the expression of cyp108j1 is negatively regulated by a LuxR (helix-turn-helix transcription factors in acyl-homoserine lactones-mediated quorum sensing) family regulator, NarL (nitrate-dependent two-component regulatory factor), which is located upstream of cyp108j1. Further analysis revealed that NarL can directly bind to the promoter region of cyp108j1. Mutational experiments demonstrated that the binding site between NarL and the cyp108j1 promoter was the palindromic sequence GAAAGTTG-CAACTTTC. Together, the finding reveal that NarL is a novel repressor for the expression of cyp108j1 during PAHs degradation.