Identification and characterization of carboxyl esterases of gill chamber-associated microbiota in the deep-sea shrimp Rimicaris exoculata using functional metagenomics

The shrimp Rimicaris exoculata dominates the fauna in deep-sea hydrothermal vent sites along the Mid-Atlantic Ridge (2,320 m depth). Here, we identified and biochemically characterized three carboxyl esterases from microbial communities inhabiting the R. exoculata gill, isolated by naïve screens of a gill metagenomic library. These proteins exhibit low to moderate identity to known esterase sequences (≤52%) and to each other (11.9-63.7%) and appear to have originated from unknown species or from genera of Proteobacteria related to Thiothrix/Leucothrix (MGS-RG1/RG2) and to the Rhodobacteraceae group (MGS-RG3). A library of 131 esters and 31 additional esterase/lipase preparations was used to evaluate the activity profiles of these enzymes. All 3 of these enzymes had greater esterase than lipase activity and exhibited specific activities with ester substrates (≤356 units mg-1) in the range of similar enzymes. MGS-RG3 was inhibited by salts and pressure and had a low optimal temperature (30°C), and its substrate profile clustered within a group of low-active and substrate-restricted marine enzymes. In contrast, MGS-RG1 and MGS-RG2 were most active at 45-50°C, were salt-activated and baro-tolerant. They also exhibited wider substrate profiles that were close to those of highly active promiscuous enzymes from a marine hydrothermal vent (MGS-RG2) and from cold brackish lake (MGS-RG1). The data presented are discussed in the context of promoting the examination of enzyme activities of taxa found in habitats that have been hitherto neglected for enzyme prospecting; the enzymes found in these taxa may reflect distinct habitat-specific adaptations and may constitute new sources of rare reaction specificities.