Firmicutes is a phylum of bacteria known for their thick cell walls, which often contain a high amount of peptidoglycan. This group includes various species, some of which are beneficial to human health, while others can cause diseases. They are commonly found in diverse environments, including soil, water, and the intestines of animals. Many Firmicutes play a crucial role in digestion, particularly in the guts of mammals, where they help break down complex carbohydrates. This phylum includes well-known genera such as Bacillus and Clostridium, which have applications in biotechnology and medicine.