# Microbial Life on the Surface of Microlgistics in Natural Waters
## 7 Role Microorganisms of Degradation of Plastic  
It is known that most plastics are non-biodegradable. For example, the biodegradation of polythene bags consisted of just 4.2% after 9 months of incubation in mangrove soil, and microbial species involved in the process of biodegradation were representatives of bacterial genera _Streptococcus_, _Staphylococcus_, _Microococcus_, _Moraxella_, and _Pseudomonas_ and fungal species of the genus _Aspergillus_[105]. Plastic is considered as non-degradable material due to (1) high molecular weight which makes impossible transportation of large molecules through the cell membrane of microorganisms; (2) high hydrophobicity which prevent attachment of microbial cells to hydrophilic surfaces; (3) lack of proper functional groups [63; 106]. Although many recent studies have focused on the microbial biodegradation of microplastic in water, there are no positive results proving participation of marine microorganisms in this process. However, it was found that sequences from such bacterial genera as _Klebsiella_, _Pseudomonas_ and _Sphingomonas_ were more abundant in biofilm on microplastic in effluent from WWTP than in sewage, so it can be due to the ability of these microorganism to use microplastics as growth substrates which leads to their degradation [94]. Thus, sequences from the genus _Sphingomonas_ were 10-fold more abundant on microplastic taken from effluent compared to microplastic found in sewage. Meanwhile, bacteria from the genus _Sphingomonas_ can degrade plastic. _Sphingomonas pauc immobilis_ isolated from Lake Nakuru, Kenya, degrade polythene and plastics, 37.5% and 17.5%, respectively, after ninety days of degradation [107]. However, several recent studies showed that some bacteria and fungi are capable of degrading certain types of plastic. It was reported that bacterial strain with high cell-surface hydrophobicity _Rhodococcus ruler_ C208 can degrade polyethylene film up to 8%, and the addition of mineral oil increased biodegradation by about 50% [108]. Some authors reported that microorganisms capable of decomposition and consuming inert materials which are very difficult to degrade in the environment could be found in the biofilms on microplastic particles. Thus, microorganisms capable of degrading hydrocarbons with the content up to 17% were found in the biofilms on polypropylene, and polystyrene microplastic particles in the Mediterranean Sea [71]. Microorganisms able to degrade lignin were found in biofilms covered with microplastic particles [70; 83]. Very often bacteria capable of degrading hydrocarbon contaminants were present in the microbial communities attached to MRs. Several hydrocarbon-degrading bacteria were identified in the plastisphere of plastic marine debris collected in the North Atlantic [80]. Bacteria of genera _Arcobacter_ and _Colwellia_ which degrade hydrocarbon contaminants within low-temperature marine environments were detected on low-density polyethylene microplastics [108]. Bacteria from the genus _Olebacter_ were found to be dominated among microbial communities in microplastic biofilm [67]; meanwhile it is known that this genus includes species capable of degrading hydrocarbons [109; 110]. Biofilm of microplastic from effluent of WWTP had more representatives of genera _Klebsiella_, _Pseudomonas_, and _Sphingomonas_ compared to influent microplastic [94]. Meanwhile, it was found that _Pseudomonas_ and _Sphingomonas_ strains are capable of degrading polycyclic aromatic hydrocarbons [111]; strain _Sphingomonas pauc immobilis_ Sy isolated from mangrove sediment degrades dimethyl terephthalate that is used in the manufacturing of polyethylene terephthalate (PET) [112], and bacterial strain _Klebsiella pneumoniae_ was able to degrade high-density polyethylene (HDPE) [113]. The bacterial genus _Erythbroacter_,known for the ability to utilize polycyclic aromatic hydrocarbons, was found on microplastics [86].