Microorganisms are classified into different groups based on the temperature ranges. Temperature is one of the essential factors in the growth rate, multiplication, survival, and death of living organisms, among other factors.
Microbes cannot control their internal temperature, as it is always the same as the outside temperature, in contrast to pH or osmolarity. The temperature changes affect enzymes and their activity.
- Low temperature: At this temperature, organisms can survive and replicate. The microbial membrane gets solidified, and enzymes do not function properly. If the outside temperature is lower than the optimal temperature, it can decrease enzyme activity and slow the metabolism.
- Optimum temperature: At optimum temperature, the organism’s growth rate is higher as it leads to the fastest metabolism.
- High temperature: At extreme temperatures, organisms can grow. This temperature can disrupt the microbial membrane. It can damage microbes by denaturing proteins, such as enzymes, transport carriers, and other proteins, leading to cell death.
What are Mesophiles?
Mesophiles “Meso means middle” and “philes means loving” are microorganisms that grow and thrive at mild temperatures.
The term “mesophile” was first used in written form in the 1900s. In a 1901 paper by Charles Theodore Mohr, OED first reported the existence of mesophiles.
Mesophiles grow in the temperature ranges between 20°C and 45°C (68 and 113 °F), which are neither too hot nor too cold.
- The optimum temperature is 37°C (the body temperature of warm-blooded animals).
- Such as, Pseudomonas aeroginosa can grow at lower temperatures (5°C- 43°C).
- Thermal death point for mesophilic bacteria is 50°C-65°C.
- Mesophiles can reproduce sexually with male and female bacteria and replicate by cell division through mitosis. It can double its number in approximately 20-30 minutes at the optimum temperature, pH, and salinity.
- Since it can express mammalian proteins, expand plasmid DNA, and produce extremophilic enzymes or extremozymes, Escherichia coli is the most common mesophile used to express heterologous proteins. This allows for an increase in enzyme production.
Mesophiles Habitat
The habitat of these organisms includes cheese and yogurt, and they are also in the brewing and wine-making processes.
Most pathogenic microorganisms and normal human microbiomes, such as species of bacteria, fungi, and even archaea, are belongs to this mesophile group.
Examples are Staphylococcus aureus, Escherichia coli, Streptococcus pneumoniae, Listeria monocytogenes, Streptococcus pyogens, Thiobacillus novellus, Clostridium kluyveri, Salmonella spp., Lactobacillus spp., Proteus vulgaris, Pseudomonas maltophilia, Thiobacillus novellus, and Haemophilus influenzae.
Advantages
Mesophilic bacteria are involved in biodegradation. They are active at the temperature ranges from 20°C–45°C used for biodegradation (digestion and decomposition of organic matter).
- It decomposes vegetable and animal matter and forms a humus layer in forests and other fertile soils.
- At first, psychrophilic bacteria start decomposition because they are active at the lower temperature below 20°C and generate heat.
- When the temperature reaches the range of 20°–45°C (50- 100°F), it attracts mesophilic bacteria to carry on the biodegradation process.
- At the temperature ranges of 30–37°C (86–99°F), reproductive and mesophilic bacteria activity is at peak level, and the temperature of the soil environment increases. Then, thermophilic bacteria take place.
A beneficial bacteria or probiotic organism found in human intestinal flora is Lactobacillus acidophilus, a dietary factor, which is a mesophilic bacterium.
In dairy industries, Lactic acid bacteria play a crucial role. Its fermentation helps in making cheese and yogurt. Mesophilic Lactobacillus species are used in washed-rind cheese, and hard or semi-hard cheese because of their amino peptidase activity, which imparts flavor and helps lessen bitterness during cheese maturation.
In cheese making, Lactococcus lactis (Lc. lactis), dominant acidifying mesophile species, and Leuconostoc mesenteroides ssp. cremoris, a weakly acidifying culture, is used in some (fresh) dairy fermentation processes to add flavor. Lactococcus lactis has two subspecies, namely cremoris and lactis. Lc. lactis cremoris.
- Modern selection technique stated that many Lc. Lactis ssp. lactis is better for good flavors because of its faster lactic acid production rate.
- Lactic acid bacteria are Lactococcus lactis ssp. lactis, Lactococcus lactis ssp. lactis (-cit+), Lactococcus lactis ssp. cremoris, Leuconostoc mesenteroides ssp. cremoris.
Some mesophilic organisms are used in brewing industries (beer production) to soak a starch source, like maize involving specific yeast strains, which help to convert starch into ethanol.
- In the brewing industries (wine and beer production), mesophilic yeast activity is optimal at low-temperature fermentation 20°C–45°C.
- One of the results stated that Saccharomyces pastorianus grows well at lower temperatures, 10–12°C for beer production. In this process, there is the production of carbon dioxide and ethanol.
- The most common mesophilic yeasts are Saccharomyces cerevisiae, Brettanomyces bruxellensis, Saccharomyces pastorianus, Torulaspora delbrueckii, and Pichia anomala.
Some mesophilic bacteria are widely used as food supplements and neutraceutical preparations, innocuous to human health, to prevent gastrointestinal disorders.
Mesophilic bacteria, the Acidithiobacillus and Leptospirillum genera, are also used in bioleaching.
- The growth temperature for organisms ranges between 25 and 35°C. Both microbes are chemolithotroph, rod-shaped, gram-negative, and non-spore former.
- Acidithiobacillus uses CO2 in the air as the carbon source, while Leptospirillum Fe2+ is an energy source.
- The important Acidithiobacillus species in bioleaching are Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Acidithiobacillus caldus, Acidithiobacillus albertis, Acidithiobacillus acidophilus, Acidithiobacillus concretivorus, and Acidithiobacillus prosperus.
- It can grow in a medium as low as pH 1, which aids in the bioleaching of metal oxides and sulfides to recover metals.
- Leptospirillum spp., such as Leptospirillum ferrooxidans, can withstand a lower pH (about 1.2).
Disadvantages
Mesophilic bacteria can cause food deterioration and contamination, such as in bread, grains, dairy, and meats. At the optimum temperature, the chances of food spoilage are high because of the rapid growth of bacteria, and some may produce toxins.
- For example, Listeria monocytogenes is a mesophilic organism responsible for meat, salami, and soft-cheese spoilage.
- Escherichia coli and In addition to altering food, Clostridium kluyveri is responsible for gastrointestinal disorders.
Mesophilic bacteria are also involved in bacterial infection in humans that find their optimum growth temperature around 37°C (98.6°F).
Avoiding mesophilic bacteria
- Food cooked at an adequately high temperature should be consumed because, at high temperatures, it may destroy most organisms, although lower temperatures take more time.
- Should consume food that has been preserved in a freezer or refrigerator. In freezing temperatures, there will be no growth of organisms. In refrigerator temperature, it may allow the slow growth of spoilage bacteria.
- Prevent staphylococcus infection or transmission by maintaining good hygiene, avoiding contact with infectious materials, and refraining from sharing personal materials.
References
- https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/mesophilic-bacteria
- https://microbeonline.com/psychrophiles-mesophiles-thermophiles/
- https://www.nursinghero.com/study-guides/boundless-microbiology/temperature-and-microbial-growth
- https://www.slideshare.net/mohammedzahid3/microbial-growth-57494714
- https://www.slideshare.net/MariyaRaju/extremophiles-76837205
- https://doi.org/10.1016/B978-0-12-818307-6.00008-1
- https://doi.org/10.1007/978-3-642-40872-4_1610-2
- https://doi.org/10.1016/B0-12-227055-X/00194-2
- https://www.slideshare.net/MAMATHESH/food-spoilage-microbiology
- https://www.slideshare.net/vishalvlk/bacterial-physiology-54592936
