# Marine Bacteria Associated with Colonization and Alteration of Plastic Polymers
## 1 Introduction  
Bacteria are pioneering organisms in plastic surface colonization. Some approaches have been carried out for study of colonization of plastic debris by bacteria [1, 2] and the existence of bacteria growth and plastic-associated microbial assemblages on diverse polymer surfaces such as polypropylene, polystyrene and polyethylene has been demonstrated [3, 4, 5].  
Bacteria colonization is associated with production of extracellular polysaccharide substances (EPS) which reduce ionic repulsive forces between bacteria and polymer surfaces [6]. In some cases, EPS production has been detected while no polymer alteration was observed [7]. Otherwise, bacteria, such as _Pseudomonas_ sp., _Kocuria_ sp. and _Bacillus_ sp., can form biofilms and facilitate the breakdown of polymer-associated chemical compounds [8]. Hence, bacteria could play a role in the colonization and possible alterations of polymer because of their occurrence on marine plastic debris. Studies of plastic-colonizing bacteria would thus provide useful information for knowing how bacteria act and their potential influence on biofilm abundance and plastic alteration.  
Marine bacteria associated with plastics are predominantly identified through molecular characterization using the 16S rRNA gene. Bacteria from sand from coastal areas, where plastics accumulate most [9], can be thus assumed as the main colonizers of \(\leq 5\) mm plastic surfaces as identification of bacteria detached from microplastics during the separation procedure in a laboratory is not feasible.  
In addition, microplastics take a longer time to alter due to the presence of salt and due to slow buildup of heat in the samples in sea water [10, 11]; thus, its persistence providesa habitable environment for microorganisms. Plastic debris can suffer cleavage of bonds through processes of hydrolysis and oxidation and address the formation of new chemical groups [12]. Polymer oxidation from biotransformation results in toxic compounds that are harmful for human health and impact natural environments [13]. Moreover, polymer alteration includes changes in polymer chemical structure that can lead to chemical bond weakening and loss of properties [14]. Polystyrene (PS) and polypropylene (PP) are polymers used in several industries and with commercial applications. They are the kind of plastic most reported at the drift line above sea water level [2].  
Analytical procedures to monitor plastic polymer alteration include a microbiological approach such as EPS determination and chemical analyses through Fourier transform infrared spectroscopy (FTIR) [15]. Fourier transform infrared spectroscopy analysis can show chemical modifications of the polymer structure and the formation of new chemical groups because of microbial attack [16; 17].  
This study aimed at isolation and molecular identification of bacteria that are able to colonize plastic polymer in order to evaluate the alteration of plastic polymers by bacteria. Our goal is to identify predominant bacteria through the 16S rRNA gene that are associated with marine sand at the drift line where most plastic debris is deposited. Moreover, polymer colonization by bacteria is evaluated in in vitro assays through EPS production and by increment in weight of polymers. Commercial polystyrene and polypropylene spheres are chosen as representative polymers and structural alteration due to in vitro colonization by bacteria is analyzed through FTIR.