Chapter 19, Problem 1Q

Can aerobic bacteria grow in the absence of ${\text{O}}_{\text{2}}$ ? _________________ What would you need to do to determine whether bacteria growing on a Petri plate from the Brewer jar are anaerobes?

Summary Introduction

To determine:

If aerobic bacteria can grow in the absence of oxygen andthe method to determine whether bacteria growing on a Petri plate from the brewer jar is anaerobes.

Introduction:

Bacteria is a single-celled microscopic organism that belongs to the prokaryotic domain. They show diversity in their niche and cellular features. Bacteria can survive in aerobic, anaerobic or both conditions (facultative anaerobes). Facultative anaerobes can switch mechanisms to adapt to the environment.

Explanation of Solution

Strict aerobes can only survive in the presence of oxygen, but they can thrive for a short duration in the absence of oxygen too. Some aerobes can switch mechanism to use another terminal electron acceptor instead of oxygen.

Brewer jar is an anaerobic chamber for culturing anaerobes. Atmospheric oxygen is removed from the jar by chemically combining it with hydrogen to release water. The bacteria growing in Petri plates from brewer jar can be tested for anaerobes by subculturing them in aerobic conditions or thioglycolate medium. The subculture of anaerobes would not be able to survive in aerobic conditions whereas thioglycolate broth is a nutrient-rich differential medium used for differentiating aerobic and anaerobic microorganisms. The presence of sodium thioglycolate in the medium allows the growth of obligate anaerobic organisms by consuming the dissolved oxygen. This results in the creation of an anaerobic environment at the bottom of the culture tube. Aerobic organisms thus accumulate at the top of the broth to obtain atmospheric oxygen whereas the obligate anaerobes accumulate at the bottom of the tube where the oxygen is completely absent.

Conclusion

The bacteria growing in Petri plates from brewer jar can be tested for anaerobes by subculturing them in aerobic conditions or thioglycolate medium.