Fluorescence images (IMAGE) Max-Planck-Gesellschaft Caption Purple sulfur bacteria in freshwater Lake Cadagno (upper panels, in green and purple), and their single-cell nitrogen fixation activity measured with nanoSIMS (lower panels, warm colors indicate high activity). Credit Max Planck Institute for Marine Microbiology/M. Philippi Usage Restrictions Usage in connection with the press release only. License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.