Are cyanobacteria classified as gram-negative bacteria?

Yes, cyanobacteria are classified as gram-negative bacteria. This classification is based on the structure of their cell walls, which contain a thin layer of peptidoglycan surrounded by an outer membrane. When stained using the Gram staining technique, cyanobacteria appear pink or red under a microscope, indicating that they do not retain the crystal violet stain and are therefore gram-negative.