Eco-friendly Organic Nanotubes Encapsulating Alkaline Phosphatase and Ecotoxicology of Nanotubes to Natural Bacterial Assemblages in Coastal Estuarine Waters

Abstract

Phosphatase-encapsulated nanotubes have potential in environmental remediation of organophosphate contaminants (e.g., pesticides, nerve agents). We investigated alkaline phosphatase (AP) activity when encapsulated in self-assembled lithocholic acid nanotubes (LCA-AP) in water samples along a transect from Cypress bog headwaters through estuarine waters and to Atlantic Ocean seawater. Apparent V max (app V max) for both LCA-AP and unencapsulated AP (Free-AP) was most rapid at mid-estuary and most inhibited at the humic-rich bog. LCA-AP retained a higher-activity percentage, suggesting that encapsulation may afford some protection from denaturing effects of humics. Apparent K m (app K m)­ of Free-AP (1–2.3 μM) was largely unaffected by preincubation with transect water, whereas app K m of LCA-AP was higher with bog water (5.3 μM) relative to other stations. When comparing Free-AP and LCA-AP, increasing salinity generally decreased the catalytic efficiency of the LCA-AP, but had little effect on that of the Free-AP. In addition, both showed the same pattern of lowest efficiency in bog water, which increased with salinity to 21 practical salinity units before decreasing at full-strength salinity. With the exception of the similarly low values in the bog water (1.04 for LCA-AP, 1.34 for Free-AP), absolute values of catalytic efficiency for LCA-AP were about 17% (range: 14.5–19.3%) of that for Free-AP. Nanotube addition had little ecotoxicological effect on heterotrophic bacterial production in waters sampled along the transect. Microbially associated, intrinsic AP activity showed a similar pattern along the transect to LCA-AP, suggesting that AP environmental control and regulation in nature may inform study of nanomaterials.