What are examples of helpful bacteria

Bacteria that are extremely helpful are bacteria of decay.
Without these microorganisms, dead organic matter would never re-enter the ecosystem and
enrich the soil as humus. This in turn would affect all of the operating food webs on
Earth. Also, the planet would be covered in garbage and the cycles of carbon and
nitrogen would be interrupted as well. Decomposers are in integral part of the
biosphere. Some of the "good bacteria" in our intestines help to keep the numbers of
fungi like yeast in check. Without them, an overgrowth of yeast could result in an
infection. Some bacteria enable us to make foods like yogurt and cheese, via the process
of fermentation. Nitrogen fixing bacteria are important because they change atmospheric
nitrogen into nitrates which is a form of nitrogen plants can absorb and use to
manufacture plant proteins. These can be consumed in food webs by animals which in turn
can be used  to make animal proteins. Bacteria get a bad reputation sometimes, but
Kingdom Eubacteria  have members that we just can't live without. Bacterial DNA can be
genetically engineered to produce endless supplies of human growth hormone, insulin and
other drugs relatively quickly to improve the human condition.