Despite inherent strain the cyclobutane motif is indeed found in nature. One unusual example is "pentacycloanammoxic acid", which is a ladderane composed of 5 fused cyclobutane units. The estimated strain in this compound is 3 times that of cyclobutane. The compound is found in bacteria performing the anammox process where it forms part of a tight and very dense membrane believed to protect the organism from toxic hydroxylamine and hydrazine involved in the production of nitrogen and water from nitrite ions and ammonia. Some related fenestranes are also found in nature.