Mechanism of TonB-dependent transport system in Halomonas alkalicola CICC 11012s in response to alkaline stress

New insights into the typical nitrogen-containing heterocyclic compound-quinoline degradation and detoxification by microbial consortium: Integrated pathways, meta-transcriptomic analysis and toxicological evaluation

As the primary source of COD in industrial wastewater, quinoline has aroused increasing attention because of its potential teratogenic, carcinogenic, and mutagenic effects in the environment. The activated sludge isolate quinoline-degrading microbial consortium (QDMC) efficiently metabolizes quinoline. However, the molecular underpinnings of the degradation mechanism of quinoline by QDMC have not been elucidated. High-throughput sequencing revealed that the dominant genera included Diaphorobacter, Bacteroidia, Moheibacter and Comamonas. Furthermore, a positive strong correlation was observed between the key bacterial communities (Diaphorobact and Bacteroidia) and quinoline degradation. According to metatranscriptomics, genes associated with quorum sensing, ABC transporters, component systems, carbohydrate, aromatic compound degradation, energy metabolism and amino metabolism showed high expression, thus improving adaptability of microbial community to quinoline stress. In addition, the mechanism of QDMC in adapting and resisting to extreme environmental conditions in line with the corresponding internal functional properties and promoting biogegradation efficiency was illustrated. Based on the identified products, QDMC effectively mineralized quinoline into low-toxicity metabolites through three major metabolic pathways, including hydroxyquinoline, 1,2,3,4-H-quinoline, 5,6,7,8-tetrahydroquinoline and 1-oxoquinoline pathways. Finally, toxicological, genotoxicity and phytotoxicity studies supported the detoxification of quinoline by the QDMC. This study provided a promising approach for the stable, environmental-friendly and efficient bioremediation applications for quinoline-containing wastewater.

Halo-alkaliphilic microbes as an effective tool for heavy metal pollution abatement and resource recovery: challenges and future prospects

The current study presents an overview of heavy metals bioremediation from halo-alkaline conditions by using extremophilic microorganisms. Heavy metal remediation from the extreme environment with high pH and elevated salt concentration is a challenge as mesophilic microorganisms are unable to thrive under these polyextremophilic conditions. Thus, for effective bioremediation of extreme systems, specialized microbes (extremophiles) are projected as potential bioremediating agents, that not only thrive under such extreme conditions but are also capable of remediating heavy metals from these environments. The physiological versatility of extremophiles especially halophiles and alkaliphiles and their enzymes (extremozymes) could conveniently be harnessed to remediate and detoxify heavy metals from the high alkaline saline environment. Bibliometric analysis has shown that research in this direction has found pace in recent years and thus this review is a timely attempt to highlight the importance of halo-alkaliphiles for effective contaminant removal in extreme conditions. Also, this review systematically presents insights on adaptive measures utilized by extremophiles to cope with harsh environments and outlines the role of extremophilic microbes in industrial wastewater treatment and recovery of metals from waste with relevant examples. Further, the major challenges and way forward for the effective applicability of halo-alkaliphilic microbes in heavy metals bioremediation from extremophilic conditions are also highlighted.

Cadmium sulfide nanoparticle biomineralization and biofilm formation mediate cadmium resistance of the deep-sea bacterium Pseudoalteromonas sp. MT33b

Cadmium (Cd) is a common toxic heavy metal in the environment, and bacteria have evolved different strategies to deal with Cd toxicity. Here, a bacterium designated Pseudoalteromonas sp. MT33b possessing strong Cd resistance was isolated from the Mariana Trench sediments. Supplement of cysteine significantly increased bacterial Cd resistance and removal rate. Biofilm formation was demonstrated to play a positive role toward bacterial Cd resistance. Transcriptome analysis showed the supplement of cysteine effectively prevented Cd²⁺ from entering bacterial cells, promoted saccharide metabolism and thereby facilitating energy production, which consists well with bacterial growth trend analysed under the same conditions. Notably, the expressions of many biofilm formation related genes including flagellar assembly, signal transduction, bacterial secretion and TonB-dependent transfer system were significantly upregulated when facing Cd stress, indicating their important roles in determining bacterial biofilm formation and enhancing Cd resistance. Overall, this study indicates the formation of insoluble CdS precipitates and massive biofilm is the major strategy adopted by Pseudoalteromonas sp. MT33b to eliminate Cd stress. Our results provide a good model to investigate how heavy metals impact biofilm formation in the deep-sea ecosystems, which may facilitate a deeper understanding of microbial environmental adaptability and better utilization of these microbes for bioremediation purposes in the future.