Metroid Remix: Brinstar East is based off the Super Metroid track: Brinstar Overgrown with Vegetation Area, originally composed by Kenji Yamamoto and Minako Hamano.

This was the track made for the (cancelled) Metroid Remix Project I was involved in a while back. This was used in Brinstar East.

On another note, at 2:22 there is an 'unusual' add-on in the track. While I could source it, I will let the comments dept. do it on my behalf, to see if anyone is paying attention. :)

UPDATE: Zaltaire has correctly guessed where the 'extra bit' is from. Good job! :)