Cyanobacteria, often referred to as blue-green algae, are diverse microorganisms found globally. The genus Nostoc frequently appears in terrestrial settings, leading many to question its safety.
Identifying Nostoc
Nostoc is a distinctive cyanobacterium recognized by its gelatinous appearance. When wet, it typically forms spherical, sheet-like, or irregular masses, ranging from dark green to black. These moist colonies are often called “star jelly” or “witch’s butter.” Upon drying, Nostoc masses shrivel into an inconspicuous, crisp brownish or black crust. However, these dried forms can quickly rehydrate and swell to their gelatinous state after rainfall or when exposed to moisture.
Nostoc thrives in various moist habitats, including damp soil, rocks, pathways, and garden beds. It is commonly observed in areas with compacted soil or poor drainage where water collects. Nostoc can also be found in aquatic environments, such as freshwater ponds, brackish water, and marine settings. It can colonize diverse regions, from polar zones to arid areas, surviving extreme conditions like drought and freezing.
Assessing Safety Concerns
For most people encountering Nostoc in gardens or lawns, it is not considered harmful. Common mat-forming species like Nostoc commune are not toxic to plants or animals. The primary concern is its slippery texture when wet, which can create a physical hazard.
Nostoc belongs to the broader group of cyanobacteria, some of which produce potent compounds called cyanotoxins. Certain Nostoc species or strains can produce toxins such as microcystins, nodularins, and Beta-Methylamino-L-alanine (BMAA). Microcystins and nodularins are hepatotoxins, primarily affecting the liver, while BMAA is a neurotoxin. Toxin production may be influenced by environmental stress conditions.
Despite the potential for some Nostoc species to produce these compounds, the risk of harm from casual contact in a garden environment is low. Some Nostoc species, notably Nostoc commune and Nostoc flagelliforme, have been traditionally consumed as food in various cultures, particularly in Asia and parts of South America, valued for their protein, vitamins, and amino acids. However, ongoing scientific discussion exists regarding BMAA in some edible Nostoc species and its potential association with neurodegenerative diseases. This underscores the need for specific identification before consumption.
Guidance for Encountering Nostoc
When encountering Nostoc, general hygiene practices are advisable. Avoid consuming any unknown environmental organisms. If handling larger quantities, particularly during garden or landscape maintenance, wearing gloves is recommended.
To manage unwanted Nostoc, several approaches can be used:
- Improving drainage in affected areas, such as amending compacted soil, aerating lawns, or adjusting landscape levels to prevent water pooling.
- Reducing excessive watering and increasing sunlight exposure to damp areas to discourage growth.
- Physical removal, such as scraping it off paved surfaces or scooping it from garden beds.
- Reducing soil phosphorus levels, as this nutrient promotes Nostoc development.