Microbiology

Step 1: Understanding Biofertilizers.
Microorganisms act as biofertilizers by promoting the growth of plants through natural processes. Some of the key roles microorganisms play as biofertilizers include:
1. **Nitrogen Fixation**: Certain bacteria like Rhizobium convert atmospheric nitrogen into a form that plants can use, thus enriching the soil with nitrogen.
2. **Phosphorus Solubilization**: Microorganisms like Bacillus and Pseudomonas help in solubilizing phosphorus from insoluble compounds, making it available to plants.
3. **Organic Matter Decomposition**: Fungi and bacteria decompose organic matter in the soil, releasing essential nutrients for plant growth.

Step 2: Conclusion.
By improving soil fertility and nutrient availability, microorganisms play a vital role in sustainable agriculture as biofertilizers.

Step 1: Understanding the process.
Lactobacillus is a type of bacteria responsible for converting lactose in milk into lactic acid, which causes the milk to curdle, forming yogurt or curd.

Step 2: Conclusion.
Thus, the correct answer is option (2) Lactobacillus.