IN-SITU FILTRATION AND PRELIMINARY MOLECULAR ANALYSIS OF MICROBIAL BIOMASS FROM THE RAINBOW HYDROTHERMAL PLUME AT 36-DEGREES-15'N ON THE MID-ATLANTIC RIDGE

Elevated microbial biomass levels play a significant role in altering the chemical composition of hydrothermal plumes. In this work, a proce dure was developed for collecting sufficient quantities of microbial b iomass from a hydrothermal plume to allow the extraction of DNA suitab le for use in molecular analyses of the plume microbial populations. D uring a geophysical survey along 200 km of the Mid-Atlantic Ridge (MAR ), southwest of the Azores Triple Junction, several new sites of hydro thermal activity were identified, including the Rainbow hydrothermal p lume, at 36 degrees 15'N, the strongest such feature yet reported from the MAR. During the survey, in situ filtration systems were used to c ollect microbial biomass from the crater column onto 293 mm diameter, 0.2 mu m-pore membrane filters by pumping large volumes (300-500 1) of seawater through the filters. Filter samples were collected from both the neutrally buoyant portion of the Rainbow plume (at a depth of 205 0 m) and from above it in the water column (at 1500 m). Microgram quan tities of genomic DNA were extracted and purified from the biomass on these filters. The suitability of the purified DNA for use in molecula r analyses was demonstrated by polymerase chain reaction (PCR) amplifi cation of the small subunit ribosomal rRNA (SSU rRNA) gene from the tw o primary prokaryotic domains, the Bacteria and the Archaea. As indica ted by the binding of domain-specific oligonucleotide hybridisation pr obes to the purified DNA, the plume microbial populations contained a higher proportion of members of the domain Archaea than the population s in the surrounding ambient sea-water. (C) 1998 Elsevier Science B.V. All rights reserved.