# Harnessing Biotechnology for the Remediation of Organic Pollutants in Coastal Marine Ecosystems
## 4 Biotechnological Methods for Remediation
### Bioremediation  
Bioremediation, also referred to as microbial remediation, is the application of microbes such as bacteria, fungi and archaea to reduce organic pollutants into less harmful compounds. These microorganisms possess enzymatic systems that metabolize contaminants and often utilize them as carbon or energy sources [18]. Bioremediation is generally divided into approaches which are in situ or ex situ; in situ denotes remediation at the location of the contaminant, while ex situ transfers contaminants to other places for remediation. Considering the cost of transport, bioremediation of contaminants is preferentially conducted in situ [53]. Bioremediation is further divided into biostimulation, bioaugmentation, and bioattenuation.  
Biostimulation involves the addition of nutrients such as nitrogen and phosphorus or the adjustment of environmental conditions like pH and oxygen levels to enhance the metabolic activity of indigenous microorganisms, thereby optimizing degradation processes [54]. For example, nitrogen-rich fertilizers are often applied during oil spill incidents to stimulate hydrocarbon-consuming bacteria. On the other hand, bioaugmentation involves introducing specific strains of microorganisms with superior pollutant-degrading abilities to contaminated sites [55]. This approach is particularly relevant when the indigenous microbial populations are insufficient or ineffective in degrading certain contaminants. In some cases, genetically engineered microbes are developed to target persistent organic pollutants such as polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), leading to their degradation [56].  
The bioremediation of antibiotics is primarily facilitated by bacteria such as _Pseudomonas_ spp., _Bacillus_ spp., _Acinetobacter_ spp. and _Streptomyces_ spp. [57]. These microorganisms utilize peripheral metabolic pathways, including hydrolysis, oxidation and deamination, to break down antibiotic structures, making them more accessible for degradation. Once modified, central metabolic pathways, particularly the tricarboxylic acid (TCA) cycle, facilitate the complete mineralization of antibiotic derivatives, ensuring their removal from the environment.  
Similarly, PCBs, which are persistent organic pollutants, are degraded by microorganisms such as _Burkholderia xenovororans_, _Pseudomonas putida_, and _Rhodococcus_ spp. [58]. The primary peripheral pathway involved in PCB degradation is the biphenyl degradation pathway, where dioxygenase enzymes oxidize PCBs into chlorobenzene4 [59]. These intermediates are subsequently processed through central metabolic pathways, including the \(\beta\)-ketoadipate pathway, which channels them into the TCA cycle for further breakdown. This mechanism is crucial for reducing the toxic effects of PCBs and preventing their accumulation in ecosystems.  
In the case of PAHs, microbial degradation is primarily driven by microbes like _Mycobacterium vanbaelnii_, _Spingomonas_ spp., _Stentrophomonas_, _Brevbacterium_, _Arthrobacter_, _Rhodococcus_, and _Pseudomonas aeruginosa_[60, 61, 62]. These bacteria initiate the degradation process through peripheral pathways involving dioxygenase enzymes, which convert PAHs into catechols and quinones [62]. These intermediates are then funneled into central pathways, such as the \(\beta\)-ketoadipate pathway or the TCA cycle, allowing for their complete mineralization. Since PAHs are highly hydrophobic and resistant to degradation [63], microbial bioremediation offers an effective strategy for their removal from contaminated environments.  
Table 2 presents representative microorganisms involved in the bioremediation of various pollutants. It highlights the peripheral metabolic pathways used to break down contaminants.