There are no bacteria on other bacteria. Some bacteria do attack other bacteria by piercing their cell wall and injecting proteins. Viruses can attack bacteria. They are called bacteriophages.
Some bacteria will consume other bacteria, but in general, individual bacterium are simple enough organisms that they break down entirely on their own.
bacteria is, unless you were to use the word "The" in front (the bacteria are)
Answer
The bacterium is ...., the bacteria are..... Bacteria is the plural form, bacterium is the singluar.
yes, it depends on the species of the bacteria. Some bacteria can produce toxin to inhibit the growth or kill the other bacteria if the bacteria doesn't have the specific anti-toxin.