There was an article a while back (probably 6 or 7 months ago) in AFM
about this same thing. The story ran, I believe, in 2 consecutive
issues. It had to do with the use of molecular probes, a technology not
previously available to researchers. I too found this to be very
interesting. Apparently, according to this particular researcher, it
has always been assumed that Nitrosomonas and Nitrobacter were the
organisms responsible for the nitrogen cycle, since they were
responsible for it in non-aquatic environments. The article went on to
say (if I remember correctly) that they haven't found the responsible
organisms due to their inability to obtain pure cultures
Jim