Pure water does not contain DNA. Water is a simple inorganic compound, while deoxyribonucleic acid (DNA) is a complex biological macromolecule. However, natural water bodies frequently contain genetic material from living organisms. This genetic material, known as environmental DNA or eDNA, offers a powerful tool for understanding aquatic ecosystems.
The Nature of DNA and Water
DNA serves as the genetic blueprint for life forms, carrying the instructions for an organism’s development, functioning, growth, and reproduction. It is a complex macromolecule composed of repeating nucleotide units, each containing a sugar, a phosphate group, and a nitrogenous base. This structure forms the double helix, found within cells of living organisms.
Water, in contrast, is a chemical compound made up of two hydrogen atoms and one oxygen atom. It is an inorganic molecule, different from the carbon-based organic molecules that constitute DNA. Pure water lacks the carbon backbone, nitrogenous bases, and phosphorus to form DNA. Water functions as a solvent, providing the medium in which biological processes occur, not a biological entity itself.
Environmental DNA in Water
Environmental DNA (eDNA) refers to genetic material that organisms shed into their surroundings, not directly sampled from an individual. This includes DNA from shedding skin cells, feces, urine, mucus, gametes, or decaying tissues. In aquatic environments, this genetic material disperses into the water column, sediment, or air.
Many aquatic organisms contribute eDNA, including fish, amphibians, invertebrates, and microorganisms. Fish constantly shed cells and other biological traces into the water as they swim and feed.
eDNA persistence in water varies, ranging from less than one day to a few weeks, depending on environmental conditions. Factors like ultraviolet radiation, acidity, temperature, and microbial activity influence eDNA degradation. Despite its transient nature, eDNA indicates the source organism was likely in the area recently.
Applications of Environmental DNA
Detecting eDNA in water is important for ecological monitoring and conservation. One primary application is species detection, confirming the presence of specific species without direct observation or capture. This is useful for elusive, rare, or endangered species difficult to find through traditional survey methods. For example, eDNA has been used to detect endangered fish species and elusive mammals.
eDNA plays a role in broader biodiversity monitoring, providing a comprehensive snapshot of the aquatic community. Analyzing eDNA, scientists can assess ecosystem health and diversity, identifying often-overlooked microorganisms and invertebrates. This non-invasive approach is more sensitive and cost-effective than conventional methods, as a single water sample can reveal multiple species.
eDNA is a valuable tool for tracking invasive species, enabling early detection before widespread establishment. Identifying these species at low densities allows for timely and effective management. To analyze eDNA, water samples are collected and filtered. The DNA is then extracted and amplified using molecular techniques like Polymerase Chain Reaction (PCR) and DNA sequencing. Sequenced DNA is compared to genetic databases to identify source organisms.