Question

Regulation by Recombination In the phase variation system of Salmonella, what would happen to the cell if the Hin recombinase became more active and promoted recombination (DNA inversion) several times in each cell generation?

Short answer

Increased recombinase activity causes frequent flagellar type switching, aiding immune evasion.

Step-by-step solution

Understanding Phase Variation

Phase variation in Salmonella involves the inversion of a DNA segment controlled by the Hin recombinase, which alters the expression of flagellar proteins.

Role of Hin Recombinase

The Hin recombinase is an enzyme that promotes recombination (inversion) of a specific DNA segment, allowing Salmonella to switch between two different forms of flagellar proteins, aiding in immune evasion.

Effect of Increased Activity

If Hin recombinase became more active, it would lead to more frequent inversions of the DNA segment, causing Salmonella to alternate more frequently between the two flagellar protein forms.

Consequences of Frequent Inversions

Frequent inversions due to increased recombinase activity would likely cause Salmonella to change its surface proteins more often, potentially resulting in better evasion of the host's immune response but also possible instability in protein expression.

Conclusion

Increased Hin activity would enhance Salmonella's ability to avoid immune detection by varying its surface proteins but may also result in unpredictable surface protein profiles.

Key concepts

DNA recombination

DNA recombination is a fascinating process where segments of DNA are rearranged to create genetic diversity. This rearrangement can happen naturally and plays a crucial role in evolution and adaptation. Recombination involves the crossover of genetic material which leads to new traits in organisms. For example, when different versions of the same gene shuffle, they can lead to new characteristics which can be beneficial for survival.

In the context of the phase variation system of Salmonella, DNA recombination is controlled by an enzyme called Hin recombinase. This enzyme specifically targets a section of DNA and flips it – a process known as DNA inversion. This inversion allows Salmonella to switch its flagellar proteins, which are crucial for motility and survival. By altering these proteins, the bacteria can effectively adjust its surface characteristics to better adapt to changing environments.

Phase variation

Phase variation is a neat trick used by bacteria like Salmonella to avoid the immune system of a host. It is essentially a genetic switcheroo, where the organism alternates between different expressions of genetic traits to stay under the radar of its host's immune defenses. Specifically, Salmonella toggles between two types of flagellar proteins.

The mechanics of phase variation depend heavily on DNA recombination processes, like those facilitated by the Hin recombinase. Through the inversion of DNA, phase variation allows for the rapid transition between different protein expressions. This variability provides a survival advantage by preventing long-term recognition and destruction by the immune system.

Enzyme activity

Enzymes, like the Hin recombinase, are proteins that speed up or control various biological processes. In the case of DNA recombination, Hin recombinase specifically targets and inverts DNA segments, which is critical for phase variation. The activity level of such enzymes is crucial; if too low, they might not catalyze required reactions efficiently, and if too high, they could cause excessive changes.

In the Salmonella phase variation system, increased Hin recombinase activity would mean more frequent inversion events. This could allow Salmonella to cycle rapidly through its variant protein expressions, enabling it to adapt more quickly to immune pressures. However, this might also lead to an imbalance in protein expression, potentially causing harm to the bacterium's consistency and stability of its functions.

Immune evasion

Immune evasion is a survival strategy utilized by many pathogens, including bacteria like Salmonella. The objective is to avoid detection and destruction by the host's immune system, allowing the pathogen to thrive and propagate. Salmonella achieves this using the mechanism of phase variation, facilitated by DNA recombination.

By continuously switching the proteins present on its surface, Salmonella can elude the host immune cells, much like a chameleon blending into its surroundings. This ability to rapidly change through enhanced recombinase activity makes it difficult for the immune system to develop an effective response. Thus, while frequent DNA recombination could cause instability, it’s a trade-off that enables successful immune evasion, granting Salmonella a persistent edge in survival.