Factors that influence the growth of microorganisms • Temperature Temperature determines the activity of enzymes involved in chemical activities. Temperature increase 10oC is able to increase activity by 2 times. At very high temperatures, irreversible protein denaturation will occur (irreversible), on the other hand, at very low temperatures, enzyme activity will stop.Bacteria can grow at various temperatures from near freezing to near the boiling point of water. Bacteria that grow best in the middle of this range are referred to asmesophiles, which includes all human pathogens and opportunists. There are three types of bacteria based on their level of tolerance to environmental temperature, namely: 1) psychrophile, namely microorganisms that like to live in cold temperatures, can grow best at optimum temperatures below 20oC; 2)mesophyll, namely microorganisms that can live optimally at moderate temperatures, have an optimum temperature between 20-50oC; 3)thermophile, namely microorganisms that grow optimally or like high temperatures, these microorganisms often grow at temperatures above 40oC. • pH Increases and decreases in the concentration of hydrogen ions can cause ionization of protein, amino and carboxylate groups, which can cause protein denaturation which disrupts cell growth. Microorganismsacidophil, grows in the optimal pH range of 1.0-5.3, microorganismsneutrophils, grows in the optimal pH range of 5.5-8.0, microorganismsalkalophil, grows in the optimal pH range of 8.5-11.5, while microorganismsextreme alkalophilegrows in the optimal pH range > 10. • Osmotic pressure Osmosis is the movement of water through a semipermeable membrane due to an imbalance of dissolved material in the medium. In solutionhypotonic, water will enter the cells of microorganisms, whereas in solutionhypertonic, water will come out of the microorganism cells, resulting in the plasma membrane shrinking and detaching from the cell wall (plasmolysis), the cell is metabolically inactive. Microorganisms that are able to grow in hypertonic environments with high sodium levels are known ashalophile, for example bacteria in the sea. Microorganisms that are able to grow at very high salt concentrations (> 33% NaCl) are calledextreme halophile, for example Halobacterium halobium. • Oxygen Based on oxygen requirements, they are known as aerobic and anaerobic microorganisms. Microorganismsaerobicrequire oxygen to breathe, while microorganismsanaerobesdoes not require oxygen to breathe, in fact the presence of oxygen will inhibit its growth. Microorganismsfacultative anaerobes, useoxygen as respiration and fermentation as an alternative but with low growth rates. Microorganismsmicroaerophiliccan grow well with oxygen less than 20%. • Radiation The source of radiation on earth is sunlight which includes visible light, ultraviolet radiation, infrared rays and radio waves. Radiation that is dangerous for microorganisms is ionizing radiation, namely radiation from very short and energetic wavelengths that causes atoms to lose electrons (ionization). At low levels ionizing radiation can cause mutations that lead to death, while at high levels it is lethal. • Nutrition Nutrients are substances needed for biosynthesis and energy formation. There are two types of nutrition for microorganisms, namely macrolements and microelements.Macroelementsare nutritional elements that are required in large quantities (grams). Macroelements include carbon (C), oxygen (O), hydrogen (H), nitrogen (N), sulfur (S), phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca), and iron ( Fe). C, H, O, N, and P are needed for the formation of carbohydrates, fats, proteins, and nucleic acids. K is required by a number of enzymes to synthesize proteins, and Ca+plays a role in the resistance of bacterial endospores to heat.Microelementsnamely nutritional elements required in small quantities (in mg to ppm), including manganese (Mn), zinc (Zn), cobalt (Co), nickel (Ni), and copper (Cu). Microelements are sometimes part of enzymes or cofactors that help catalyze and form proteins.