Biological dark matter is an informal term for unclassified or poorly understood genetic material.
By extension, biological dark matter may also refer to the un-isolated microorganisms whose existence can only be inferred from the genetic material that they produce.
[32] A comprehensive study of DNA sequences from multiple human samples inferred the existence of 4,930 species of microbes of which 77% were previously unreported.
[33] Health-related findings include a prophage that might be associated with cirrhosis of the liver,[27] and seven novel sequences from children with type-1 diabetes that have characteristics of viruses.
In February 2023, scientists reported the findings of unusual DNA strands from the microorganisms in the "dark microbiome" in the driest non-polar desert on Earth.