What is the gas released by cyanobacteria

Cyanobacteria /saɪˌænoʊbækˈtɪəriə/, also known as Cyanophyta, are a phylum of bacteria that obtain their energy through photosynthesis,[4] and are the only photosynthetic prokaryotes able to produce oxygen.[5] The name "cyanobacteria" comes from the color of the bacteria (Greek: κυανός, translit. kyanós, lit. 'blue').[6][7] Cyanobacteria (which are prokaryotes) used to be called "blue-green algae". They have been renamed 'cyanobacteria' in order to avoid the term "algae", which in modern usage is restricted to eukaryotes.[8]

he is very short, and he can only reach halfway up on the elevator buttons. but on a rainy day, he has his umbrella with him, and he uses it to poke the button at the top.