Microbial distribution and activity at vents

The aerobic and anaerobic heterotrophic microbes present at vents often have complex nutrient requirements (e.g. organic acids, carbohydrates, elemental sulphur) some are believed to be mixotrophic, using both autotrophic and heterotrophic metabolisms (Karl, 1995 Kelley etal., 2002). Organic matter in sulphide mineral chimneys may come from other dead and/or pyrolysed microbes and invertebrates (e.g. worm tubes and muccus) during growth of chimneys. At most hydrothermal sites, thermal environments at moderate temperatures (50-90°C) are 

Microbial diversity in chimneys may be high, as suggested by novel cell morphologies, presence of mixed communities and development of biofilms, as viewed by scanning electron microscopy (SEM Chevaldone, 1996 Harmsen etal., 1997 Delaney etal., 2001), and more recently by phylogenetic studies (Harmsen etal., 1997 Delaney etal., 2001 Takai etal., 2001). Community structure (diversity and density) in chimneys can vary on a scale of a few centimetres and likely reflects the formation of environmental gradients of temperature, pH, redox potential and chemistry (Takai etal., 2001). 

Inactive chimneys, hydrothermal and sulphide sediments and mounds The interior of sulphide mounds has been likened to an exposed mesoscale view of the subsurface environment, and hence is of great interest to microbiologists (Deming Baross, 1993). This environment may also provide a continuum of bacterial populations between high and low temperature hydrothermal 

Reysenbach etal. (1998) found microbes in the first metre of drill core from TAG (ODP Leg 158) and were able to produce enrichment cultures of hyper-thermophilic, S-reducing organisms, but they could not rule out that these organisms were entrained by fluids. Samples of deeper (i.e. 1-52m), hotter parts of drill core produced no microbial growth and cell counts were too low to be reliable. Microbial communities were also found to exist in sulphide sediments from inactive parts of TAG, and they are presumed to be involved in cycling of S, Fe and Mn there (Severmann etal., 2000). 

---