Profile – Firmicutes


The name Firmicutes is derived from the Latin words for firm (firmus) and skin (cutis), which suits this group because of their rigid cell wall, which supports their well-defined shape. Firmicutes are typically round (coccus) or rod-long (bacillus) in shape.

Many Firmicutes produce endospores. Unlike fungal spores, Firmicute endospores are not involved in reproduction, but are produced for self-preservation. Under stressful conditions, Firmicutes can enter a dormant state by shrinking into an endospore. As an endospore, these bacteria are resistant to dehydration, ultraviolet radiation, extreme temperatures and even anti-bacterial substances. They remain this endosporic state until the conditions in their surroundings improve. As endospores, bacteria can stay alive for long periods of time. In fact, there is even a documented case in the United States where Firmicutes found in an underground salt crystal dated to be 250 million years old were revived.

The group Firmicutes have been found to make up the largest portion of the human gut biome and as such have been harnessed intensely for food production. A special group of Firmicutes, called Lactobacillus (plural: Lactobacilli), is a key ingredient in the production of yoghurt, cheese, sourdough bread, beer, kimchi and other fermented foods. Lactobacillus consumes sugars and converts them into lactic acid. The acid produced gives these foods their signature sour taste. Salt-tolerant Lactobacilli are also used to preserve food and it is the combination of salt water and lactic acid makes it harder for other microbes to grow.

Unfortunately, Lactobacilli are also the main culprits behind beer spoilage. The growth of these bacteria in beer increases its cloudiness, acidity (through lactic acid) and produces an unsavoury odour. Then again, it’s also thanks to Firmicutes that we have delicious sour beers!

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Bacterial profiles: Proteobacteria | Actinobacteria | Acidobacteria | Tenericutes | Firmicutes