Could extreme pollution drive to new catalityc activities on microbial esterases?

Abstract

Modern life thrives in lots of extremes, such as deep-sea vents, hot springs and high salt environments. Furthermore, as a consequence of human activity, new extreme environments of anthropogenic origin can be considered. That could be the case of PolyAromatic Hydrocarbon (PAH) contaminated soils or waters. PAHs are pollutants of great importance because of their toxicity, mutagenicity and carcinogenicity, and are widely distributed due to their abundance in crude oil and their widespread use in chemical industries. In the past years a number of microorganisms able to use PAHs as a sole carbon source have been described and new enzymes, mainly oxygenases, implicated in PAH degradation have been identified. Herein a versatile esterase (CN1E1) from the α/β-hydrolase family (Martínez-Martínez et al., 2014) was isolated from an anthropogenically influenced and PAH-contaminated soil (Guazzaroni et al., 2013). The protein shares low-to-medium identity (≤ 57%) with known esterase/lipase-like proteins. The enzyme is most active at 2–30°C and pH 8.5; it retains approximately 55% of its activity at 4°C and less than 8% at ≥ 55°C, which indicates that it is a cold-adapted enzyme. CN1E1 has a distinct substrate preference compared with other α/β-hydrolases because it is catalytically most active for hydrolysing polyaromatic hydrocarbon (phenanthrene, anthracene, naphthalene, benzoyl, protocatechuate and phthalate) esters (7,200–21,000 units g−1 protein at 40°C and pH 8.0). The enzyme also accepts 44 structurally different common esters with different levels of enantioselectivity. The results provide the first biochemical evidence suggesting that such broad-spectrum esterases may be an ecological advantage for bacteria that mineralize recalcitrant pollutants (including oil refinery products, plasticizers and pesticides) as carbon sources under pollution pressure (e.g. Alcaide et al., 2013). They also offer a new tool for the stereo-assembly (i.e. through ester bonds) of multi-aromatic molecules with benzene rings that are useful for biology, chemistry and materials sciences for cases in which enzyme methods are not yet available.