1) Gram-negative bacterium 
The Proteobacteria are a major group (phylum) of bacteria. They include a wide variety of pathogens, such as Escherichia, Salmonella, Vibrio, Helicobacter, Yersinia, and many other notable genera. Others are free-living (non-parasitic), and include many of the bacteria responsible for nitrogen fixation. Carl Woese established this grouping in 1987...
phylum of gram-negative bacteria