How did Orochimaru turn Jugo's ability into the curse mark?
Jugo is not the original bearer of the curse mark. He's the source from whom that jutsu was created. Jugo's clan had a special body which could absorb the force of nature and transform into various forms and had immense urge to kill.



Like said on Chapter 349, page 9, Orochimaru used Jugo's blood to create an enzyme that caused similar transformations and gave immense power to the bearer. Orochimaru just injected the enzyme into his subjects.