IODP Proceedings    Volume contents     Search


Conclusion and future prospects

Using FCM together with microscopic observations for cell counting has confirmed that subsurface sediment in the South Pacific Gyre harbors significantly lower microbial concentrations than previously reported for any other subseafloor sediment. The use of FCM for onboard cell counts was tested for the first time in the history of scientific ocean drilling. This technique has a great potential for high-throughput onboard cell enumeration. In addition to providing more robust estimates of cell abundance, cell size data were also collected. This is significant in that cell size can provide more accurate estimates of biomass than cell abundance. The method appears to work well for relatively high numbers of cells (>104 cells/cm3) in sediment. However, the method still needs methodological improvement and standardization, including detection sensitivity and quality of chemical reagents, for accurate counts of extremely low cell numbers in subsurface habitats, like South Pacific Gyre subsurface sediment. In a shore-based study, cell numbers of all sediment samples prepared during Expedition 329 will be recounted with a new method using FCM and verified with other established methods, such as image-based microscopic cell count and microscopic direct count.