True unicellular extremophiles capable of living in the full spectrum of temperatures, chemical soups and atmospheres. They form a kaleidoscopic range of patterns and colours based on their method of metabolism. They derive energy from photosynthetic, chemosynthetic or thermosynthetic processes. There are believed to be the precursors for many life forms, and are often found in conjunction with other species. Links between the biochemistry of bacterial colonies and neighbouring organisms are likely but as yet unproven.
Bacterium can be very hard to find, as it tends to blend into the terrain. A good trick is to use the free cam on an SRV to get a bird's-eye view of the area while driving, and patches of Bacterium should stick out like a sore thumb.