The most abundant prokaryotes helpful to human in making curd from milk and in production of antibiotics are the ones categorized as
(3) chemosynthetic autotrophs
(4) heterotrophic bacteria
(4) Heterotrophic bacteria are most abundant in nature. Many of them have a significant impact on human affairs. These are helpful in making curd from milk (e.g., Lactobacillussp.), production of antibiotics (e.g., Streptomyces sp.) and fixing nitrogen in legume roots (e.g., Rhizobium spe).