According to Official Guinness Records,
The most alkaline-resistant lifeform is a bacterium discovered in 2003 near Chicago, Illinois, USA. It lives in groundwater contaminated by more than a century of industrial iron slag tipping where it can survive pH levels of up to 12.8.
They were discovered by scientists at the Illinois State Water Survey and announced at a conference of the Geological Society of American in Seattle, Washington in November 2003.
For a complete list of 2003 records, please visit 2003 Guinness Records in United States.