Bacteria is very useful in producing food. In fact, bacteria helps in the production of all the produce, cereals, etc., by keeping the soil enriched with nutrients.
A specific example of this is seen with legumes (including lentils, peas, beans, soybeans, etc.) which are common protein rich food. These plants form a symbiotic relationship with nitrogen-fixing bacteria in the soil. The bacteria enrich these crops with nitrogen by fixing nitrogen from the atmosphere into a form usable by the plant.
Another example of bacteria used in food production is that of making yogurt (or curd). Lactobacilli are commonly used for this purpose throughout the world. Dried (and fermented) meat products such as salami, pepperoni, etc. are made by using starter cultures. For this purpose lactic bacteria are used, which add flavor and color to the dried meat.
A large number of other examples especially from the dairy industry can also be used.
Hope this helps.