Industrial microbiology — selecting a bulk medium for submerged bacterial fermentation In large-scale submerged bacterial fermentation (commercial production), which of the following is most commonly employed as the principal medium/carbon source due to cost and nutrient profile?

Introduction / Context:
Commercial submerged fermentation demands inexpensive, readily available media that consistently support high cell density and product yields. Industrial microbiology therefore favors agro-industrial byproducts such as molasses and corn steep liquor because they provide fermentable sugars, minerals, vitamins, and growth factors at scale and at low cost.

Given Data / Assumptions:

• We are considering standard bacterial submerged (liquid) fermentations at commercial scale.
• Economics, supply stability, and nutrient composition drive medium choice.
• Typical pairings include beet/cane molasses (carbon) with corn steep liquor (nitrogen and vitamins).

Concept / Approach:
Molasses (beet or cane) contains high percentages of sucrose, glucose, and fructose, plus minerals that support rapid bacterial growth. It is easily pumped, sterilized, and blended, making it ideal for fed-batch control of carbon to limit overflow metabolism. Liver extract and germinated seeds are nutrient-rich but impractical and costly at industrial tonnage.

Step-by-Step Solution:
Identify the most common, low-cost carbon source used globally: molasses.Recognize that beet molasses is widely used interchangeably with cane molasses depending on region and market.Conclude beet molasses best fits the prompt's emphasis on “commonly used” at commercial scale.

Verification / Alternative check:
Process descriptions for antibiotics, organic acids, and enzymes frequently list molasses plus corn steep liquor as the baseline medium for seed and production stages.

Why Other Options Are Wrong:
Liver extract and germinated seed are nutrient sources but are not economical or widely standardized for bulk bacterial fermentations; “none” contradicts established practice; corn steep liquor alone lacks sufficient fermentable carbohydrate and is usually paired with molasses.

Common Pitfalls:
Assuming laboratory-rich media (for example, tryptone/yeast extract) scale economically; industrial media prioritize price, availability, and process control over maximal richness.

Final Answer:
Beet molasses.