What are the most diverse and widespread prokaryotes?

The most diverse and widespread prokaryotes are bacteria and archaea. Bacteria exhibit a vast range of shapes, metabolic pathways, and ecological roles, thriving in diverse environments from extreme heat to deep ocean vents. Archaea, often found in extreme conditions like hot springs and salt lakes, also contribute significantly to global biogeochemical cycles. Together, these groups play crucial roles in ecosystems, human health, and biotechnology.