• Acartia tonsa
• copepod microbial hotspot
• 16S metabarcoding
• predictive functional metagenomic profiling
• PBSA degradation
• Vibrio sp.
• Cladosporium sp.
• bio-based polyester

Acartia tonsa is a crustacean belonging to the subclass Copepoda, order Calanoida, which feeds mainly on phytoplankton through filtration of the water column. The feeding strategy facilitates the continuous turnover of macro- and micronutrients, promoting bacterial colonization, therefore, Acartia tonsa represents a microbial hotspot. At the end of the life cycle, the bacterial communities associated with carcasses of this species show lipase, protease, and chitinase activities involved in the degradation of high molecular weight macromolecules, recalcitrants to biodegradation. These enzymes might find application in the degradation of biopolymers, interesting in this thesis, in particular poly(butylene succinate-co-butylene adipate) (PBSA), a bio-based polyester suggested as an alternative to petroleum-derived plastics, specifically, for the production of nets to support the replanting of Posidonia oceanica. In this thesis, microbial communities associated with the culture of the copepod A. tonsa, reared under controlled conditions, and fed with a monoalgal diet of Rhinomonas reticulata, were characterized. A culture-independent approach was adopted by means of 16S rDNA metabarcoding accompanied by a predictive functional metagenomics study with a particular interest in the Carboxylic-ester hydrolases activities involved in PBSA degradation. In detail, the carboxylesterase, triacylglycerol lipase and cutinase activities were investigated, providing a taxonomic and functional profile of the bacterial communities investigated. especially in the carboxylesterase, triacylglycerol lipase activities and cutinase, Attention regarded bacterial communities associated with individuals that had just reached the adult stage and those that had reached it after 7 days. In addition, bacterial communities associated with carcasses of newly formed dead individuals and after 4 and 33 days, were considered. Bacterial communities associated with carcasses differ from those associated with the alive, adult copepod A.tonsa. In particular, the data obtained suggest that the differences increase with time, in fact, the carcasses at 33 days differ significantly in taxonomic and functional terms from the bacterial communities associated with adult organisms and from recently formed carcasses. The bacterial communities associated with the copepod carcasses offer a greater contribution to the carboxyl-ester hydrolase activities and this contribution shows an important equidistribution among the bacterial taxa that characterize the carcasses formed from 33 days, not necessarily the most represented ones. A culture-dependent approach was also adopted for the isolation of microorganisms by the debris derived from dead cultures of A. tonsa. The main interest was isolating bacterial and fungal candidates that employ hydrolytic enzymatic activities involved in the degradation of PBSA. Eleven bacterial morphotypes and four fungal morphotypes were isolated and selected for their ability to use PBSA as the only carbon source. One of the bacterial morphotypes has been characterized by the genus Vibrio sp. which carries out extracellular carboxyl-ester hydrolase and lipase activities, promoting the reduction of the number of PBSA surface ester bonds. Vibrio sp. also catalyzed hydrolysis in the crystalline regions of polyester which are generally less accessible to enzymatic activities. One of the fungal morphotypes has been characterized by the genus Cladosporium sp. which perform carboxyl-ester hydrolase and lipase activities, promoting the reduction of the number of PBSA surface ester bonds and catalyzing hydrolysis of not accessible crystalline regions and more accessible amorphous region of polymers. Acartia tonsa represents a nursery of microorganisms of interest for the degradation of complex macromolecules, with possible implications for the design of processes dedicated to the transformation of recalcitrants to biodegradation, in both marine and anthropogenic environments. The latter being considered as the complex bio-based industrial processes for the transformation of recalcitrants in the environment. Of particular interest is the composting of biopolymers in the treatment of organic wastes or accelerating the biodegradation of biopolymers with potential applications in marine environment. In perspective, the further identification of fungal and bacterial morphotypes coupled with the sequencing of their genomes will allow identifying metabolic pathways potentially involved in the degradation of biopolymers, and their regulation to design innovative bio-based processes of interest for human activities in marine environment. Thus, new Culture dependent approaches will be designed for the isolation of bacterial and fungal taxa capable of PBSA degradation and other biopolymers with applications in marine environment.