# An Exploratory Review of Microplastic Pollution, Associated Microbiomes and Pathogens in Water
## 3 Results and Discussion
### Most Common Microplastic-Associated Taxa and Their Relevance  
Biofilms on microplastics (\"plastigh sphere\"--a term coined to describe the microbial biofilm that specifically forms on plastic surfaces, often enriched with unique taxa, including potential pathogens and antibiotic resistance gene carriers [93]) are largely dominated by Proteobacteria, often exceeding \(\sim\)50% of microbial communities. Numerous studies, such as those conducted by [PERSON] et al. [94], [PERSON] et al. [95], and [PERSON] et al. [96], have reported a prevalence of Alphaproteobacteria (e.g., order Rhodobacterales) and Gammaproteobacteria on plastic surfaces. Alphaproteobacteria--especially _Rhodobacteraceae_--are typical marine biofilm pioneers, contributing to biofilm matrix formation and organic matter degradation. Gammaproteobacteria include both environmentally important taxa (e.g., _Alteromonas_, _Alcanivorax_) and potential pathogens (_Vibrio_, _Pseudomonas_, _Acinetobacter_) [94; 95; 96; 97]. _Alcanivorax_ (Proteobacteria) is a well-known hydrocarbon-degrading genus that is frequently found in marine plastispheres due to its ability to degrade aliphatic hydrocarbons and possibly plastic-derived compounds [94; 95]. _Alteromonas_ and related taxa (order Alteromonas) are common in marine biofilms and help utilize dissolved organic carbon, facilitating further microbial colonization (Table 7) [94; 96]. The second most abundant plastisphere members are typically Bacteroidetes (e.g., _Flavobacteriaceae_, _Chitinophaceae_). These Gram-negative bacteria specialize in polymer and polysaccharide degradation, helping process organic matter that settles on plastics [94; 97]. On polyethylene surfaces in the Mediterranean Sea, _Bacteroidetes_ accounted for \(\sim\)22-25% of the plastisphere--much higher than in surrounding seawater [97]. Cyanobacteria also colonize microplastics in sunlit surface layers, but their abundance on plastic is often lower than in open water (e.g., \(\sim\)5% on MPs vs. \(\sim\)20% in ambient plankton), likely due to competition within the biofilm or light limitation under biofilm layers [94; 98]. Actinobacteria generally comprise a smaller fraction of the biofilm (often just a few percent), but some strains contribute to the degradation of recalcitrant compounds and may help break down plastic additives [97; 99; 100]. In freshwater, Betaproteobacteria (e.g., Burkholderiales) are often dominant, especially in nutrient-rich rivers [101]. Microplastics serve as a novel niche promoting unique microbial communities. Many dominant bacteria--such as _Alcanivorax_, _Alteromonas_, _Sphingomonas_--are known for degrading complex organic matter or even plastic components [94; 95]. _Alcanivorax_, for instance, is often enriched on marine plastics due to its ability to metabolize hydrocarbons [82]. _Pseudomonas_ and _Sphingomonas_, frequently reported on MPs, are metabolically versatile and capable of degrading polyurethane, PET, and other polymers [97; 99]. Some biofilm members (e.g., _Nitrospira_, _Methylophilaceae_) may also play roles in nitrogen and carbon cycling, turning the plastisphere into a site of nutrient transformation [100; 101]. One major concern is the presence of pathogenic or opportunistic bacteria on plastic surfaces. In marine biofilms, _Vibrio_ spp. is frequently detected--including _V. parahaemolyticus_ and strains related to _V. cholerae_. Studies show that _Vibrio_ spp. are often more abundant on floating plastic than in surrounding seawater, raising concerns that microplastics could act as vectors for human and fish pathogens [99]. In freshwater systems, genera like _Aerononas_, _Pseudomonas_, and _Acinetobacter_ pose similar risks. _Acinetobacter_ (including _A. buumanni_) is a known hospital-associated pathogen that was found to be enriched on riverine and estuarine plastics [72; 100]. Likewise, _Arobacter_ (Campylobacterota) was found on riverine MPs, suggesting the potential transport of faecal indicators or wastewater-derived pathogens even in non-wastewater sites [101].