Single-celled life without a true nucleus, the bacteria and cyanobacteria that dominate food microbiology. Their genetic material sits as one circular chromosome in the cytoplasm, unaccompanied by the membrane-bound organelles of higher cells, a stripped-down architecture that permits astonishing growth rates and metabolic versatility. From lactic fermenters to spoilage organisms and pathogens, nearly every microbe a food scientist handles belongs here. The spelling variant procaryotes appears in older literature. Understanding their physiology is the foundation of fermentation control, preservation, and food safety.