Isolation of Anaerobic Bacteria from Terrestrial Mud Volcanoes (Salse di Nirano, Northern Apennines, Italy)

Abstract

Terrestrial mud volcanoes and salses are unique inland sites of methane and saline water seepage, driven by tectonic pressure and methane from deep subsurface oil reservoirs. These structures are mainly found in active nappe tectonic zones, like in the foothills of the Northern Apennines. Fluid samples, taken anaerobically from the Nirano mud volcano field located in the foreland of the Northern Apennines, contain low numbers of bacterial cells. Representative strains were enriched under anaerobic conditions in culture media based on the composition of the mud volcano fluid. Anaerobic fermentative organisms, partially involved in cycling of sulfur compounds, namely Desulfovibrio and clostridial strains, were enriched and isolated. Two isolates of Clostridium thiosulfatireducens- and Desulfovibrio psychrotolerans-related strains were retrieved from enrichment cultures. Isolated sulfate reducers form aggregates, composed of bacterial biomass, extracellular polysaccharides and a mineral matrix. Besides some typical “contaminants” from topsoil, the Nirano mud volcano fluids contain culturable bacteria related to organisms typical for other sediments of saline systems and/or oil reservoirs.