Microbial community structure and methane cycling in mud volcanoes of Sicily, Italy
Date Issued
2015
Date
2015
Author(s)
Chiu, Yi-Ping
Abstract
The subduction of the African plate underneath the Eurasian plate along the Apennine-Maghrebian fold-and-thrust belt has created fracture network that allows for the upward migration of deeply sourced fluids and sediments to surface environments, producing dense distribution of mud volcanoes (MVs) in western part of Sicily. The MVs in the Aragona area are characterized by high abundances of hydrocarbons generated from thermal decomposition of organic matters and microbial processes. By contrast, the MVs in the Paterno area are located at the southern margin of Mount Etna in eastern Sicily, emitting gases primarily composed of magmatic CO2 and discharging brines. In this study, we employed a combination of geochemical and molecular analyses on samples collected from core sediments and bubbling fluids from MVs associated with these two different geological settings of Sicily to investigate the community assemblages and the role of microbial process in controlling methane emissions and biogeochemical cycling. Our results showed that two sulfate-to-methane transitions at depths of ≥ 8 cm and 32.5-53.5 cm were observed in the Aragona MV. The majority of microbial members at these depth intervals were taxonomically assigned to the ANME-2 group and Desulfarculus/Desulfurivibrio. For comparison, hydrogenotrophic and aceticlastic methanogenesis likely predominated over the other pathways at 8-32.5 cm, supplying methane for the overlying and underlying anaerobic methanotrophy. In the Paterno MVs, fluids and sediments were confined with the bubbling pool with limited discharge to the adjacent mud platform. Surface sediments in the mud platform would have experienced prolonged evaporation and desiccation. Microbial populations at 0.8-22.8 cm were dominated by halotolerant or halophilic aerobic methanotrophs, sulfur oxidizers and heterotrophs affiliated with Methylohalobius crimeensis, Thiohalorhabdus denitrificans and Halobacteriaceae, respectively. At depth, diverse community assemblages were recovered with fermentative and sulfate-reducing bacteria predominating over the others. Overall, the results obtained from this study demonstrated that fluid sources, pathways, and physic-chemical conditions inherited from different geological settings could shape geochemical characteristics, and microbial processes and communities in different MVs of Sicily. The stratified, complexly structured microbial communities and processes did not enable the complete removal of methane in porespace and fracture channel. Instead, net methane emission from these MVs would contribute to the greenhouse warming.
Subjects
mud volcano
microbial methane cycling
SDGs
Type
thesis