Streptococcus is among the lactic acid bacteria (LAB), who include genera such as Lactobacillus. Besides LAB many species of Streptococcus exist in the world, some with life-giving attributes and some deadly and destructive.
Streptococcus has over 150 species, often with multiple strains. Members of the genus, especially the lactic acid bacteria (LAB), function in food production. Many species influence human health and natural balance.
Some Streptococcus strains are used as probiotics or as subjects of genetic manipulation. Others have pathogenic inclinations as in meningitis or strep throat.
Origins
Streptococcus bacteria emerge over two billion years ya to evolve with other microorganisms. Streptococcus thrive in anaerobic or microaerophilic conditions. In the latter they need some oxygen, but too much kills them.
The genus is first identified in the 1870s by microbiologist Louis Pasteur. He observes the bacteria's ability to produce lactic acid during fermentation.
Streptococcus comes from the Greek "streptos" (easily bent or twisted) and "kokkos" (grain or berry). It describes the chain-like arrangement of these spherical or ovoid bacteria.
Characteristics
LAB are a specific group within this genus. They're defined by the ability to produce lactic acid as the main end-product of carbohydrate fermentation. They are Gram-positive, catalase-negative and typically non-spore forming.
Streptococcus spp. adapt to niches. Their thick peptidoglycan cell walls provide strength and protection. In many ways they affect environmental ecosystems and health.
S. pneumoniae is a main cause of pneumonia, afflicting millions each year. Streptococcus pyogenes, another pathogenic species, ferments sugars to survive in the human throat.
Habitats
Streptococcus species are found in products like cheese, yogurt and fermented pickles. In yogurt, Streptococcus thermophilus can represent up to 30% of bacterial content.
Fermented beans, sauerkraut, sourdough bread, and more get their tangy flavors due to LAB's fermentation activity. Sourdough starters can contain up to 50 species of LAB and 20 species of yeast.
Mammals: In a mammal Streptococcus spp. are a part of the normal microbiota of the mouth, digestive system and vagina, contributing to health and thwarting harmful bacteria.
Plant Surfaces: They can be isolated from soil and various plant materials, where they work in natural decomposition processes.
Eating and Excreting
Streptococcus LAB are primarily carbohydrate consumers. Streptococcus spp. are heterotrophic, depending on organic compounds for nourishment.
They feast on sugars like glucose, lactose and fructose, breaking them down as needed through fermentation. Their primary excretory product is lactic acid, the characteristic sharp taste of many fermented foods.
Motility and Survival Skills
Streptococcus LAB are non-motile. Their survival hinges on other factors.
Acid Tolerance: Their ability to thrive in acidic environments (due to lactic acid production) provides a protective advantage against other microorganisms sensitive to low pH.
Nutrient Competition: Their rapid growth and efficient use of nutrients can outcompete other bacteria.
Bacteriocin Production: Some Streptococcus LAB produce bacteriocins, antimicrobial peptides that inhibit the growth of other bacteria, including pathogens.
They rely on their ability to adhere to surfaces to colonize favored environments. One of Streptococcus's notable survival strategies is the formation of biofilms.
These are structures made up of communities of bacteria surrounded by a protective matrix. Biofilms allow Streptococcus to withstand antibiotics and other environmental stressors.
Symbiosis
Streptococcus LAB can survive independently but often form in symbiotic relationships. In yogurt production, S. thermophilus and Lactobacillus bulgaricus work synergistically. They stimulate each other’s growth and accelerate lactic acid production.
In natural ecosystems Streptococcus spp. participate in nutrient cycling. They help decompose organic matter for better nutrient availability and soil quality.
In human health, certain Streptococcus species are part of balanced digestive microbiota, and synthesizing nutrients. Streptococcus salivarius, in the mouth, contributes to oral health by inhibiting harmful bacteria.
Some like Streptococcus pyogenes can cause infections like strep throat. Many species co-exist with host organisms to support vital functions and maintain a balanced microbial community.
Relationship with Other Microbes
Streptococcus LAB often interact with other microorganisms, including yeast. In some fermented foods, yeast contributes to the flavor and aroma profile, while LAB provides acidity to inhibit growth of spoilage bacteria.
Relationships between different microbial species defines qualities of fermented products. Saccharomyces cerevisiae is a dependable yeast producing unique flavors and textures in cheese and yogurt.
The specific strains of Streptococcus used in different fermentations dictate the final product's taste, texture, and aroma. Cheese makers, for example, select certain Streptococcus cultures for their desired qualities.
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