Thermophilic carboxylesterases from hydrothermal vents of the volcanic island of Ischia active on synthetic and biobased polymers and mycotoxins

In this study, we explored microbial communities of two terrestrial hydrothermal vents of the volcanic island of Ischia (Italy), Terme di Cavascura and Maronti Beach, as a source of novel carboxylesterases. Barcoded 16S rRNA amplicon sequencing revealed highly distinct microbial communities. Analysis of enrichment cultures incubated with bio-based polyesters, polyhydroxybutyrate and polylactic acid, revealed an increase in the relative abundance of Thermus, Geobacillus, Fontimonas and Schleiferia spp.. Using these enrichment cultures, a metagenomic fosmid library was constructed in Escherichia coli and screened for carboxylesterase activity at 37, 50 and 70 Celsius. These screens identified 14 non-redundant fosmids positive for carboxylesterase activity, from which three putative hydrolases (IS10, IS11, and IS12) with low sequence similarity to known enzymes were selected for recombinant expression and biochemical characterization. Purified enzymes exhibited maximal esterase activity at temperatures 70-90 Celsius. Thus, this study has identified novel thermotolerant carboxylesterases with a broad substrate range including polyesters and mycotoxins for potential applications in biotechnology.