The correct answer is option 1, Lactic Acid Bacillus. Lactic Acid Bacillus is a type of bacteria that plays a crucial role in the acidification and curding of milk. As the name suggests, this bacterium produces lactic acid as a metabolic byproduct.

When Lactic Acid Bacillus is introduced to milk, it ferments lactose, the primary sugar in milk, into lactic acid. This acidification process reduces the pH of the milk, making it more acidic.

The presence of lactic acid creates an environment that promotes the coagulation or curding of milk. The milk proteins, particularly casein, bind together and form a solid curd. This curding process is crucial for the production of various dairy products such as cheese, yogurt, and buttermilk.

It is important to note that the other options listed in the question do not cause acidification and curding of milk. Clostridium botulinum is a bacterium that can cause food poisoning, Vibrio cholerae causes cholera, and Saccharomyces cerevisiae is a type of yeast used in brewing and baking.

Therefore, the correct answer is option 1, Lactic Acid Bacillus, as it is responsible