Cold seep enrichment yields piezotolerant, obligate hydrocarbon degraders

Deep-sea environments can get contaminated with recalcitrant petroleum hydrocarbons through different anthropogenic activities. The effects of the hydrostatic pressure in the deep sea on microbial oil degradation, the option of choice for full remediation of these environments, is poorly understood. Moreover, efficient piezotolerant oil degraders, i.e. interesting bioaugmentation candidates, have been rarely isolated so far. Here we performed long-term enrichments (100 days) of sediment taken from a natural cold seep while providing optimal conditions to sustain high hydrocarbon degradation rates (i.e. oxygen, mesophilic temperatures [20°C] and medium chain alkanes [dodecane] in abundance). Through enrichments performed at high hydrostatic pressure (HHP) [10 MPa] and ambient pressure (AP) [0.1 MPa] and by using control enrichments with marine broth, we demonstrated that both pressure and carbon source can have a big impact on community structure. In contrast to previous studies, hydrocarbonoclastic OTUs remained dominant at both AP and HHP, suggesting piezotolerance of these OTUs over the supplied pressure range. Twenty-three isolates were obtained after isolation and dereplication using matrix-assisted laser deionisation/ionisation time-of-flight mass spectrometry (MALDI-TOF MS). After re-cultivation at HHP, strain R-72943, a hydrocarbonoclastic bacterium identified as Alcanivorax venustensis, showed promising piezotolerance in axenic culture as well. Furthermore, preliminary co-cultivation tests showed synergistic growth between some isolates, a promising result for future bioaugmentation tools. Overall, more insight into the effect of HHP on oil degrading communities was obtained as well as several interesting isolates, among others a piezotolerant Alcanivorax, with which future deep-sea synthetic community remediation could be further investigated.