• Some types of Delta Proteobacteria create deadly hydrogen sulfide gas.Bacteria Colonies image by ggw from Fotolia.com
  
  Delta proteobacteria belong to two orders, Desulfovibrionales and Myxococcales, which contain ten families between the two. Both types of Delta Proteobacteria are chemoorganotrophs, which means that they get their energy from organic sources, independent of light. All animals, fungi and some other bacteria are chemoorganotrophs; the main alternative would be to depend upon photosynthesis for sustenance, as all green plants do, or various chemicals, as some other types of bacteria do.
  
  

Desulfovibrionales

• Desulfovibrionales live in mud, polluted sediments from lakes and ponds, and methane digesters. They can switch between two distinct phases: a static predatory phase, in which they do not grow but instead devote all available resources to catching food using their flagella, or appendages; and an intracellular reproductive phase, during which they split themselves into two within the limits of their cell walls, later separating entirely. During their predatory phase, these bacteria move at high speed and collide with other bacteria of similar size within their environment. Desulfovibrionales are anaerobic, meaning they do not require oxygen to live.
  
  

Myxococcales

• Myxococcales live in neutral pH soil, decaying vegetation and animal dung. Instead of direct predation, they scavenge upon other bacteria and yeasts by releasing digestive enzymes, or lysins. These lysins cause the prey's cell walls to collapse, allowing the Myxococcales to feed upon the contents of the cell. These bacteria form a colonial structure of many individual bacteria; by cooperating, the colony releases more digestive enzymes and can process food more efficiently than an individual could. Myxococcales prefer warm areas but are resilient enough to survive in the arctic tundra. They live in the soil and are strictly aerobic, meaning they require oxygen to live.
  
  

Negative Effects

• Desulfovibrionales can be an annoyance to humans because of the role they play in corrosion in our iron structures, such as pipelines, heating systems and almost any other environment that contains iron. Another way they can be a problem is due to their role as a sulfate-reducing bacteria; as part of this process, they release foul-smelling hydrogen sulfide. In very small amounts, hydrogen sulfide, or sewer gas, is relatively harmless; eye irritation, coughing and fluid in the lungs may occur, but will go away a few weeks after exposure ends. More prolonged exposure to small amounts can cause poor memory, dizziness, irritability and loss of appetite. High concentrations can actually cause death within a few breaths. Luckily, only very low dosages are likely within the home, if any, and the odor is strong and noticeable, similar to rotten eggs. High dosages are only likely to occur within the workplace. Exposure at home can be prevented by ensuring your various plumbing fixtures are maintained.