I found that there are some record in greengene database have blank taxa at certain levels.

For example:

559773 k__Bacteria;p__Cyanobacteria;c__;o__;f__;g__;s__ 551166 k__Bacteria;p__Acidobacteria;c__iii1-8;o__;f__;g__;s__ 322984 k__Bacteria;p__Marine group A;c__;o__;f__;g__;s__

What does this mean? A culturable bacteria with unknown lineage or something else?

Thanks!

Z