Bacteria is a one celled organism. Eubacteria is the largest group of bacteria and consist of rod or spherical shaped single cell bacteria that typically have a large number of flagella and are responsible for the fixation of nitrogen.
Archaebacteria is the second largest group of bacteria and is thought to be the oldest group of bacteria. Like the eubacteria they lack a cellular nucleus. Unlike eubacteria which produces nitrogen archaebacteria produces methane.
Gram positive bacteria is bacteria that stains dark blue while gram negative bacteria cannot retain the stain. Eubacteria is a gram positive bacteria which can retain a stain.