# Strategies for Enhancing Extracellular Electron Transfer in Environmental Biotechnology: A Review
## 3 Strategies for Enhancing EET in Environmental Biotechnology
### Biofilm Formation and Optimization
Based on this observation, various researchers have endeavored to enhance existing output using genetic modification of the quorum sensing (QS) system. In their study, [PERSON] et al. [57] conducted an experiment where they upregulated the rhl QS cassette of _Pseudomonas aeruginosa_. This resulted in an increase of around 1.6-fold of the optimal power generated compared to the wild-type. One study also incorporated an artificial PqsE gene into a 2-heptyl-3,4-dihydroxyquinoline QS system negative mutant of _P. aeruginosa_ and this genetic modification resulted in a significant five-fold enhancement in the maximum current density compared to the original strain [58]. Another study confirmed that external QS signals can stimulate QS and subsequently improve the electrical performance of MFCs that was established using the extremophile _Hallanarobium preavalens_[59]. A study by [PERSON] et al. [60] which investigated the impact of AHLs on the behavior of mixed-culture electroactive bacteria (EABs), found that both intrinsic and extrinsic acylhomoserine lactones functioned as regulators enhancing the electrochemical activities of EAMs [60]. The utilization of synthetic biology techniques allows for the design and fabrication of synthetic QS systems. These engineered systems can be tailored to specific environmental biotechnology applications, enabling precise control over biofilm development and electron transfer processes. QS circuits in _Escherichia coli_ have also been successfully engineered to enhance current generation in MFCs [61]. Enhancing electron transfer in environmental biotechnology through quorum sensing manipulation offers several advantages. Firstly, it can improve the efficiency and performance of microbial processes by promoting biofilm formation, which provides a stable and protected environment for microbial communities. Biofilms offer an increased area of contact that promotes the adhesion of microorganisms and facilitates the exchange of electrons between cells and electrodes or other electron acceptors/donors. Secondly, quorum sensing manipulation can enable the development of biofilms with desired characteristics, such as increased thickness or specific microbial compositions. This control over biofilm properties allows for the optimization of electron transfer rates and overall process performance. Lastly, manipulating quorum sensing pathways can also help mitigate issues associated with biofouling. The term \"b biofouling\" pertains to the undesired buildup of microorganisms on various surfaces, leading to potential disruptions in electron transfer mechanisms. By understanding and manipulating quorum sensing mechanisms, it is possible to prevent or control biofouling by promoting the growth of desirable biofilmswhile inhibiting the growth of undesirable ones. It is imperative to highlight the substantial distinctions between QS signaling molecules and electron shuttling molecules. Electron shuttles serve as redox mediators, facilitating the transfer of electrons between bacteria and electrodes. On the other hand, QS signals possess the capability to regulate the production of electron shuttling molecules but cannot function as redox shuttles themselves.