Yeast Under Threat: Pollution's Impact Explored

Yeasts are unicellular fungi that play a role in essential ecological processes such as nitrogen and sulfur cycles, phosphate solubilization, and organic matter mineralization. They are also acknowledged as plant growth promoters due to their biostimulating effects on plant growth. Yeast provides plants with amino acids, enzymes, vitamins, and cytokinins during their fermentation processes.

Yeasts are found in soil all over the world in varying quantities that can reach up to 100,000 cells per gram of soil. They are mostly found in the rhizosphere, where they can easily assimilate the carbon molecules associated with root exudates. Yeast populations in the rhizosphere are generally high, but little is known about the influence of yeasts on plant growth.

Yeasts are an obligate component of the microbial communities of both undisturbed natural soils and disturbed soils in urban ecosystems. They are an important nutrient source for other soil-dwelling protists, bacteria, insects, and nematodes. They play a crucial role in the formation of the physicochemical properties of soils, they are involved in the formation of the soil structure, in the synthesis of specific extracellular polysaccharides, in the ion exchange in the soil, in influencing the water-holding ability and fertility of the soil, and in the production of physiologically active substances in the soil.

Water pollution occurs when harmful substances—often chemicals or microorganisms—contaminate a stream, river, lake, ocean, aquifer, or other body of water, degrading water quality and rendering it toxic to humans or the environment. Water is uniquely vulnerable to pollution as it is able to dissolve more substances than any other liquid on earth.

Agricultural pollution is the top source of contamination in rivers and streams, the second-biggest source in wetlands, and the third main source in lakes. It’s also a major contributor of contamination to estuaries and groundwater. Used water is wastewater. It comes from our sinks, showers, and toilets (think sewage) and from commercial, industrial, and agricultural activities (think metals, solvents, and toxic sludge). The term also includes stormwater runoff, which occurs when rainfall carries road salts, oil, grease, chemicals, and debris from impermeable surfaces into our waterways

Yeast in polluted water

More recently, in 2023, a study was conducted to evaluate the risk of yeast infection through exposure to polluted river water. The study found that pollution levels significantly altered fungal communities and that the risk of mycosis increased with higher pollution levels. Candida glabrata and Clavispora lusitaniae occurrence was linked with pollution, and fluconazole-resistant yeast strains were recovered from river water. The study also found that the risk of yeast infection through river water exposure is highly dependent on individual susceptibility and has therefore not been well-studied.

Another 2023 study found that human exposure pathways to polluted natural water systems are diverse and frequent, typically involving activities like swimming, boating, and irrigation. The study also found that the occurrence of pathogens in natural water environments is influenced by the characteristics of the surrounding areas and various environmental factors.

Yeast in soil

Yeasts are present in below-ground sources and have been found in a variety of soil types, including extreme acid, alkaline, volcanic, and cryogenic soils. They are not usually found in large numbers in soil, but their counts can occasionally reach millions of cells per gram. Yeasts are more diverse on the biotope level and are more common in soils with higher organic matter content. They are also affected by factors such as pH, conductivity, temperature, and water availability.

Soil yeasts possess extraordinary adaptations that allow them to survive in a wide range of environmental conditions. They can be a source of yeast oils and have been used in agriculture as potential antagonists of soil-borne plant pathogens or as plant growth promoters.

Soil yeasts affect microbial and plant growth and may play a role in soil aggregate formation and the maintenance of soil structure. They also contribute to essential ecological processes such as the mineralization of organic material and the dissipation of carbon and energy through the soil ecosystem. Some soil yeasts may also play a role in the nitrogen and sulphur cycles and have the ability to solubilize insoluble phosphates, making them more readily available for plants.

The presence of soil yeasts is threatened by habitat alterations due to human activities such as agriculture, deforestation, and urbanization. Therefore, the study of soil yeasts in undisturbed or low-managed biotopes is extremely valuable.

Yeast and plant growth

Yeast is a single-celled fungus, with around 1,500 species identified. It is commonly found in soil and on plant surfaces, and is particularly abundant in sugary mediums like flower nectar and fruits.

Yeast has a positive effect on plant growth and development. When used on crops, it can increase fruit set and production, with high yield and efficiency. It can also prevent pathogenic bacteria from infecting crops and reduce the chance of crop disease.

Yeast contains a high content of protein, organic matter, minerals, glucan, mannan, and nucleic acid. Its metabolites, such as erythronic acid, cytokinin, and auxin, can stimulate the growth and development of crops.

The addition of yeast to soil increases the nitrogen (N) and phosphorus (P) content of roots and shoots. It also increases the root-to-shoot ratio in plants and induces species-specific morphological changes. For example, yeast addition has been shown to increase tillering in sugarcane and greater shoot biomass in tomato plants.

Yeast can also promote the synthesis of amino acids, soluble sugars, vitamins, and other nutritional elements in crops, while reducing the content of nitrate, heavy metals, and other harmful substances in agricultural products. This improves the taste, freshness, and storage properties of crops.

Yeast bacteria can also benefit the soil by proliferating around crop roots, secreting colloidal substances that facilitate the formation of aggregate structure in dry soil, making it loose, breathable, and able to retain water and fertilizer. Additionally, yeast bacteria can effectively decompose ammonia, phosphorus, potassium, and other substances fixed by the soil, converting them into nutrients that can be directly absorbed and utilized by crops.

Overall, yeast is an important component of agricultural production, and its use can promote crop growth and development, enhance resistance to stress, and improve the quality and storage properties of agricultural products.

Yeast and water pollution

Water pollution is a pressing issue, with natural water sources increasingly contaminated by organic compounds and microorganisms. This includes pathogenic yeasts, which pose a significant threat to human health. Yeasts are unicellular fungi that can cause yeast infections, particularly in immunocompromised individuals. While the risk of bacterial and viral infections from water exposure is well-established, the risk of yeast infections is less understood. However, studies have detected clinically relevant yeasts, including Candida albicans, in river waters globally.

Pollution alters the fungal community composition of river water. Candida glabrata and Clavispora lusitaniae, for instance, are associated with pollution. Pollution also increases the risk of mycosis, with higher water pollution levels correlating with a higher risk of infection. Furthermore, antifungal-resistant yeast strains have been recovered from polluted river water, exacerbating the potential health risks.

The presence of human waste in water is associated with large increases in the proportion of Candida yeasts. A study of 13 polluted freshwater habitats found that locations with heavy domestic waste pollution had a higher proportion of Candida yeasts. Candida isolates were in the majority at locations with high levels of human waste pollution.

Overall, water pollution poses a significant risk to human health by increasing the presence of pathogenic yeasts in water sources. Further research is needed to fully understand the risk of yeast infections from water exposure and to develop effective treatment strategies.

Yeast and health

Yeast and human health have a complex relationship. Yeast is a type of fungus, and while some types of yeast are pathogenic, others are used as nutritional supplements and even medicines. Nutritional yeast, for example, is rich in nutrients often lacking in vegetarian and vegan diets, and it's also free of gluten, soy, and sugar, making it suitable for people with food sensitivities. Brewer's yeast is also used as a nutritional supplement and may enhance energy levels and strengthen the immune system.

On the other hand, pollution can alter the composition of yeast, and polluted river water can be a source of hazardous microorganisms, including pathogenic yeasts. Exposure to polluted waters has negative effects on human health, and the risk of yeast infection through river water exposure is a concern, especially for immunocompressed individuals. Candida spp., along with other opportunistic yeasts, have been detected in rivers globally, and the ecology of clinically relevant yeasts in river water is poorly understood.

The presence of human waste in water is associated with large increases in the proportion of Candida yeasts. Candida glabrata and Clavispora lusitaniae occurrence, for example, have been linked to pollution. Fluconazole-resistant yeast strains have also been recovered from river water, and the risk of mycosis increases with higher levels of water pollution.

While pollution does not seem to affect yeast numbers, it does affect yeast composition. A study of 13 polluted freshwater habitats found that locations with heavy industrial waste pollution and heavy domestic waste pollution had large yeast populations, with Candida isolates being the majority.

Overall, yeast can have both positive and negative impacts on human health, and pollution plays a role in altering yeast composition and increasing the risk of pathogenic yeast infections.

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