What is the Difference Between Halophiles and Osmophiles

The main difference between halophiles and osmophiles is that halophiles are microorganisms that inhabit environments with high salinity whereas osmophiles are microorganisms that inhabit environments with high osmotic pressure. Furthermore, halophiles can live in salt concentration up to 30% while osmophiles can live in high sugar concentrations.

Halophiles and osmophiles are two types of microorganisms that can live in environments with low water activity. Here, water activity defines the amount of water available for hydration of materials.

Key Areas Covered

1. What are Halophiles
     – Definition, Features, Examples
2. What are Osmophiles
     – Definition, Features, Examples
3. What are the Similarities Between Halophiles and Osmophiles
     – Outline of Common Features
4. What is the Difference Between Halophiles and Osmophiles
     – Comparison of Key Differences

Key Terms

Halophiles, High Osmotic Pressure, High Salinity, Low Water Activity, Osmophiles

What are Halophiles

Halophiles are microorganisms that live in environments with high salinity. They are also known as ‘salt-loving’ organisms. Most halophiles are classified under the domain Archaea. Also, some algae such as Dunaliella salina, some fungi such as Wallemia ichthyophaga, as well as some bacteria are halophiles. Generally, halophiles contain a carotenoid known as bacteriorhodopsin, which gives a characteristic red color to them. Moreover, they expend cellular energy to exclude excess salts out from their cytoplasm, preventing the aggregation of proteins by salting out. Also, they use strategies to prevent desiccation through the movement of water out of the cytoplasm to the external environment with high salinity. Here, they accumulate osmoprotectants in the cytoplasm, maintaining the osmolarity. Or else, they undergo selective influx of potassium ions in the cytoplasm to increase the internal osmolarity.

Figure 1: Great Salt Lake, Utah

Furthermore, halophiles can live in salt concentrations that are five times higher than the salt concentration of the ocean. This type of environments occurs in the Great Salt Lake in Utah, Owens Lake in California, the Dead Sea, and in evaporation ponds. Also, these halophiles are categorized into three groups based on their ability to tolerate salinity. They are the slight halophiles, which prefer 1.7-4.8% salinity, moderate halophiles, which prefer 4.7-20% salinity, and extreme halophiles, which prefer 20-30% salinity. Generally, the salinity of the sea is 3.5%.

What are Osmophiles

Osmophiles are the microorganisms that live in environments with high osmotic pressure. They can live in environments with low water activity such as high sugar concentrations. However, these high sugar concentrations serve as a growth-limiting factor to many microorganisms. However, osmophiles, mainly yeasts and some bacteria can protect their cell against high osmotic pressure generated by these high solute concentrations.

Figure 2: Saccharomyces cerevisiae, an Osmophile

Moreover, they synthesize osmoprotectants including alcohols, sugars, amino acids, polyols, betaines, and ectoine as an adaptation to these environments. Generally, osmoprotectants compatible solutes, which are either are neutral or zwitterionic. They act as osmolytes, which maintain fluid balance and cell volume. Additionally, plants also accumulate osmoprotectants during drought periods. More importantly, osmophiles can cause spoilage in sugar, fruit juice, concentrated fruit juice, liquid sugars, honey, etc.

Similarities Between Halophiles and Osmophiles

• Halophiles and osmophiles are two types of microorganisms that can live in environments with low water activity.
• Also, they grow under high solute concentrations.
• Furthermore, both have different mechanisms to adapt to their environment.
• These organisms are phylogenetically diverse and they belong to all the three domains.

Difference Between Halophiles and Osmophiles

Definition

Halophiles refer to an organism, especially a microorganism, that grows in or can tolerate saline conditions while osmophiles refer to the microorganisms adapted to environments with high osmotic pressures, such as high sugar concentrations. Thus, this is the main difference between halophiles and osmophiles.

Significance

Moreover, halophiles can live under high salinity while osmophiles live under high osmotic pressure. Hence, this is also an important difference between halophiles and osmophiles.

Type of Environment

Halophiles can live in salt concentration up to 30% while osmophiles can live in high sugar concentrations.

Type of Organisms

Furthermore, another important difference between halophiles and osmophiles is that the halophiles are mainly archaea while osmophiles are mainly yeasts.

Adaptation to the Environment

Besides, while halophiles expend cellular energy to exclude salt from their cytoplasm, avoiding the aggregation of their proteins by ‘salting out’, osmophiles synthesize osmoprotectants such as alcohols and amino acids. Thus, this is also a major difference between halophiles and osmophiles.

Importance

Halophiles live in salt concentrations five times greater than that of the ocean while osmophiles cause spoilage in the sugar and sweet goods industry.

Conclusion

Halophiles are a type of microorganisms that can live in high salt concentrations. Mainly, archaea are halophiles and they exclude the excess salt from their cytoplasm by expending cellular energy. In comparison, osmophiles are microorganisms, mainly yeasts, that can live under high osmotic pressure. They synthesize osmoprotectants to maintain fluid balance inside the cell. Both halophiles and osmophiles are organisms with low water activity. However, the main difference between halophiles and osmophiles is the type of environment they live and their adaptations to the environment.

References:

1. Kim, J, et al. “Halophilic and Osmophilic Microorganisms.” Compendium of Methods for The Microbiological Examination of Foods, APHA Press, 2014. Available Here.

Image Courtesy:

1. “great-salt-lake-utah-usa-landscape-50603” By werner22brigitte (Pixabay License) via Pixabay
2. “Saccharomyces cerevisiae 400x img428” By A doubt – Own work (CC BY-SA 3.0) via Commons Wikimedia