Goffredi et al. have access to a natural whale fall at 2,893 m depth in Monterey Canyon, California. In this study, they were interested in characterizing the archaeal community that is present in this location and whether it changes over time compared with the community that is present in the surrounding deep-sea sediment. To do so, sediment samples with push cores were collected from directly below the whale fall and at increasing distances away from the carcass over a period of 59 months by the Tiburon, a remote submersible that is owned and operated by the Monterey Bay Aquarium Research Institute, and were then subjected to molecular and chemical analyses.
The chemical analyses revealed increased methane and decreased sulphate concentrations directly beneath the whale carcass compared with reference sediment samples. The carbon concentrations were then analysed, and it was found that organic carbon was enriched in the sediments directly below the carcass and in sediments up to 10 m away, thus forming a distinct localized zone — or 'bull's eye' — of enrichment. Analysis of the number of cells present revealed that, as expected, there was an increase in microbial abundance beneath the carcass, and a more detailed analysis using fluoresence in situ hybridization microscopy showed that up to 40% of the microbial cells present were archaea. Intrigued by the increased concentrations of methane below the carcass, the authors went on to characterize the diversity of the archaeal population using 16S ribosomal RNA sequencing, terminal restriction-fragment-length polymorphisms and quantitiative PCR of the methyl co-enzyme M reductase A (mcrA) gene. This revealed that the archaeal community was dominated by methanogenic phylotypes, including members of the Methanomicrobiales, but that over time, successional changes occurred, with a shift in the dominant phylotype from the C1-utilizing Methanococcoides to the H2-utilizing Methanogenium. Additionally, an important shift in diversity with increasing depth was observed that is indicative of active methane cycling: the methanogenic Methanococcoides were dominant in samples taken at 3–6 cm depth, whereas representatives of the methane-oxidizing ANME-3 group dominated samples taken at 9–12 cm depth.
This is a preview of subscription content, access via your institution