Question

A scientist inoculates a bacterium into a complex nutrient slant tube. The bacterium forms only a few colonies on the slanted surface but grows prolifically in the depth of the agar. Describe the oxygen requirements of the bacterium.

Short answer

Based on the growth pattern, the bacterium prefers conditions with lower oxygen levels and hence, it is an anaerobic bacterium.

Step-by-step solution

Identify Bacterial Growth Pattern

Notice the growth pattern of the bacterium. The key observation here is that the bacterium forms just a few colonies on the surface of the agar but grows abundantly in the depth of the agar.

Understanding Oxygen Requirements

Considering the bacterium proliferates deep in the agar, where oxygen level is low, while sparse growth occurs on the surface where oxygen is readily available, this indicates that the bacterium grows better in conditions with less oxygen.

Classify Oxygen Requirements

Based on the pattern of growth, this bacterium can be classified as an anaerobe as it prefers conditions with low oxygen.

Key concepts

Anaerobic Bacteria

Anaerobic bacteria are a fascinating type of bacteria that thrive in environments where oxygen levels are low or completely absent. Unlike aerobic bacteria, which require oxygen for growth, anaerobic bacteria can grow and reproduce without it. This makes them well-suited to niche habitats, such as the depths of thick nutrient agar or the human intestine, where oxygen is scarce.
There are several types of anaerobic bacteria based on their oxygen tolerance:

• **Obligate anaerobes**: These bacteria are harmed or killed by oxygen. They can only grow in completely oxygen-free environments.
• **Facultative anaerobes**: While they prefer anaerobic conditions, these bacteria can survive and grow in the presence of oxygen.
• **Aerotolerant anaerobes**: These can tolerate the presence of oxygen but do not use it for growth.

Understanding these differences is crucial in microbiology, particularly in the medical field, where anaerobic bacteria can be both common inhabitants and dangerous pathogens.

Bacterial Growth Patterns

Bacterial growth patterns can reveal much about a bacterium's environmental preferences, including its oxygen requirements. These patterns are observed based on colony formation in different sections of media like agar.
In experiments like the one described, if bacteria mainly grow at the bottom of a nutrient agar, it indicates a preference for low-oxygen conditions. This is typical of anaerobes. Conversely, if bacteria flourish on the surface, they likely require oxygen.

• Growth at the surface: Suggests aerobic bacteria.
• Growth throughout the agar: May indicate facultative anaerobes.
• Growth exclusively at the bottom: Typical of obligate anaerobes.

Understanding these patterns helps scientists determine not only the oxygen requirements but also aids in identifying bacterial species during an experiment.

Nutrient Agar

Nutrient agar is a simple yet essential medium used for growing bacteria in the laboratory. It consists of beef extract, peptone, and agar, creating a supportive environment for a wide variety of bacterial species. One of the key features of nutrient agar is its ability to support both aerobic and anaerobic bacterial growth, depending on how it is used. By adjusting the oxygen availability, scientists and researchers can cultivate different types of bacteria and observe their growth patterns.

• Its solid form makes it easy to observe colony morphology.
• Nutrient agar can be enriched with additional nutrients when studying bacteria with specific needs.
• It's widely used in both educational and research settings due to its versatility.

Bacteria that prefer low-oxygen environments, like the mentioned anaerobe, may be better observed when the agar is left unstirred or the plate is placed in anaerobic jars to limit oxygen exposure.