members of the prokaryotic kingdom Monera. A diverse group of mostly single-celled and microscopic organisms that show great metabolic diversity, including autotrophic and heterotrophic and aerobic and anaerobic forms. Organisms in this group reproduce both sexually and asexually. Bacteria are divided into the Eubacteria (or true bacteria) and the Archaebacteria, the actinomycetes, mycoplasmas, rickettsias and the spirochates.

Alternative forms for bacterium : bacteria, kingdom Monera.