9.5 Other Environmental Conditions that Affect Growth
3 min read•june 18, 2024
Microbes face constant challenges, adapting to survive in diverse environments. They use clever strategies like accumulating and adjusting cell structures to maintain balance in both high and low conditions.
is crucial for microbial growth, with different organisms thriving at various levels. Understanding this helps us preserve food and control microbial growth. Light and chemical energy sources fuel microbial metabolism, shaping their diverse lifestyles and ecological roles.
Osmotic Pressure and Water Activity
Microbial adaptation to osmotic pressure
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- Osmotic pressure is the pressure needed to stop net water movement across a semipermeable membrane
- High osmotic pressure environments have low water concentration ()
- Low osmotic pressure environments have high water concentration ()
- Microbes adapt to high osmotic pressure (hyperosmotic) environments by:
- Accumulating compatible solutes () in their cytoplasm
- Amino acids (proline), sugars (trehalose), and potassium ions help maintain cell and prevent water loss
- Synthesizing cell wall components that increase rigidity and prevent cell lysis ()
- Accumulating compatible solutes () in their cytoplasm
- Microbes adapt to low osmotic pressure (hypoosmotic) environments by:
- Possessing in their cell membrane
- Allows for rapid efflux of solutes (ions) to prevent cell lysis due to water influx
- Having in their cell membrane to facilitate controlled water movement
- Possessing in their cell membrane
- refers to the relative concentration of solutes inside and outside the cell, affecting
- In hypertonic environments, cells may undergo , where the cell membrane shrinks away from the cell wall due to water loss
Water activity in microbial growth
- Water activity () is the ratio of water vapor pressure in a substance to pure water vapor pressure at the same temperature
- Ranges from 0 to 1, with pure water having an of 1
- Microbes require a minimum water activity for growth
- Most bacteria require > 0.90
- Filamentous fungi () and yeasts (Saccharomyces) can grow at lower (0.70-0.85)
- () can grow at even lower due to their adaptations to high osmotic pressure
- Food preservation methods that reduce water activity:
- Drying or dehydration (raisins)
- Adding solutes (salt, sugar) to create a hypertonic environment (jams)
- Freezing, which converts water to ice and reduces available liquid water (frozen vegetables)
Light Utilization and Energy Generation in Microorganisms
Light utilization by microorganisms
- use light as an energy source for growth
- use light energy to fix carbon dioxide into organic compounds
- (), purple and (Chromatium, Chlorobium) use photosynthetic pigments (chlorophyll, bacteriochlorophyll) to capture light energy
- use light energy to generate ATP but require organic compounds as a carbon source
- Purple and green non-sulfur bacteria (Rhodospirillum, Chloroflexus) use bacteriochlorophyll and carotenoids to capture light energy
- use light energy to fix carbon dioxide into organic compounds
- use chemical compounds as an energy source for growth
- oxidize inorganic compounds to generate energy and fix carbon dioxide into organic compounds
- Nitrifying bacteria (Nitrosomonas) and sulfur-oxidizing bacteria (Beggiatoa) obtain energy by oxidizing ammonia and hydrogen sulfide, respectively
- oxidize organic compounds to generate energy and require organic compounds as a carbon source
- Most bacteria (Escherichia coli) and fungi (Saccharomyces cerevisiae) are chemoheterotrophs that obtain energy and carbon from organic compounds like sugars and amino acids
- oxidize inorganic compounds to generate energy and fix carbon dioxide into organic compounds
Energy generation mechanisms
- is used by photoautotrophs to convert light energy into chemical energy
- is a process used by many microorganisms to generate ATP through the creation of a proton gradient across a membrane
- are fundamental to energy generation in both phototrophs and chemotrophs, involving the transfer of electrons between molecules
Key Terms to Review (40)
Aquaporins: Aquaporins are specialized water-channel proteins found in the cell membranes of many organisms, including plants and animals. They facilitate the rapid and selective movement of water molecules across the membrane, playing a crucial role in regulating water balance and homeostasis within cells and tissues.
Aspergillus: Aspergillus is a genus of mold commonly found in the environment that can cause infections, particularly in immunocompromised individuals. These fungi are known for producing conidia, which can be inhaled and lead to respiratory issues.
Barophiles: Barophiles are microorganisms that thrive in high-pressure environments, such as deep-sea habitats. They have adapted mechanisms to survive and grow under extreme pressure conditions.
Chemiosmosis: Chemiosmosis is a key process in cellular respiration and other environmental conditions that affect microbial growth. It is the movement of protons (H+ ions) across a selectively permeable membrane, down their electrochemical gradient, to drive the synthesis of ATP, the energy currency of the cell.
Chemoautotrophs: Chemoautotrophs are a type of microorganism that can obtain their energy by oxidizing inorganic chemical compounds, rather than relying on organic compounds or sunlight like other organisms. This allows them to serve as the primary producers in certain ecosystems, forming the base of the food chain.
Chemoheterotrophs: Chemoheterotrophs are a type of organism that obtain their energy and organic carbon compounds from the chemical breakdown of complex organic molecules. They rely on external sources of organic carbon, such as glucose or other organic compounds, to meet their energy and carbon needs for growth and metabolism.
Chemotrophs: Chemotrophs are organisms that obtain their energy by the chemical oxidation of inorganic or organic compounds. They are a type of chemotroph that use chemical energy to drive their metabolic processes, in contrast to phototrophs which use light energy.
Chlamydomonas nivalis: Chlamydomonas nivalis is a species of green algae known for causing the phenomenon called 'watermelon snow' due to its reddish pigment. It thrives in cold environments, particularly in alpine and polar regions.
Compatible Solutes: Compatible solutes are organic compounds that certain organisms, particularly extremophiles, accumulate within their cells to help maintain cellular function and integrity under environmental stresses. These solutes are called 'compatible' because they can be present at high concentrations without interfering with or denaturing cellular macromolecules and processes.
Cyanobacteria: Cyanobacteria are a group of photosynthetic, gram-negative bacteria found in various aquatic environments. They play a significant role in oxygen production and nitrogen fixation.
Dunaliella salina: Dunaliella salina is a type of halophilic green microalgae that thrives in high-salinity environments. It is known for producing large amounts of carotenoids, particularly beta-carotene.
Green sulfur bacteria: Green sulfur bacteria are a group of anaerobic, phototrophic bacteria that use sulfur compounds as electron donors for photosynthesis. They belong to the phylum Chlorobi and thrive in light-deprived, anoxic environments such as deep-sea hydrothermal vents or stratified lakes.
Halobacteria: Halobacteria are a class of extremophilic archaea that thrive in highly saline environments. They are known for their unique adaptations to high salt concentrations, such as specialized cell membrane proteins and enzymes.
Halobacterium: Halobacterium is a genus of halophilic Archaea that thrive in environments with high salt concentrations. They are known for their distinctive red or pink pigmentation due to the presence of bacteriorhodopsin.
Halomonas: Halomonas is a genus of halophilic (salt-loving) bacteria found in various saline environments such as salt flats, seawater, and salted foods. These bacteria are known for their ability to thrive in high-salt conditions that inhibit the growth of many other microorganisms.
Halophiles: Halophiles are microorganisms that thrive in high-salt environments, such as salt lakes and salt mines. They have adapted mechanisms to maintain cell integrity and functionality despite the osmotic stress caused by high salinity.
Halophiles: Halophiles are organisms that thrive in high-salt environments, typically requiring at least 0.2 M (1.2%) sodium chloride for optimal growth. These specialized microbes have evolved unique adaptations to survive and function in conditions with elevated salinity.
Halotolerant: Halotolerant organisms can survive and grow in environments with high salt concentrations, although they do not require such conditions for growth. They are capable of maintaining cellular function despite osmotic stress induced by salt.
Hyperosmotic: Hyperosmotic refers to a solution or environment that has a higher osmotic pressure than the surrounding medium, causing water to move out of cells and into the external environment by osmosis.
Hypersaline: Hypersaline refers to environments with extremely high salt concentrations, often exceeding that of seawater. These conditions can significantly impact microbial growth and survival.
Hypoosmotic: Hypoosmotic refers to a solution or environment that has a lower osmotic pressure or concentration of dissolved solutes compared to another solution or the interior of a cell. This creates an imbalance where water tends to flow into the cell or organism to equalize the osmotic gradient.
Mechanosensitive Channels: Mechanosensitive channels are specialized membrane proteins that act as gateways, opening and closing in response to mechanical stimuli, such as changes in pressure or tension within the cell or its surrounding environment. These channels play a crucial role in the perception and transduction of various environmental signals that affect the growth and survival of microorganisms.
Osmoprotectants: Osmoprotectants are organic compounds that help organisms maintain cellular homeostasis and adapt to osmotic stress by regulating the movement of water across cell membranes. They are particularly important in the context of environmental conditions that affect microbial growth.
Osmosis: Osmosis is the spontaneous movement of water molecules across a semi-permeable membrane from a region of higher water concentration (lower solute concentration) to a region of lower water concentration (higher solute concentration), driven by the difference in solute concentrations on the two sides of the membrane.
Osmotic pressure: Osmotic pressure is the force exerted by solutes in a solution on a semipermeable membrane, driving the movement of water. It is crucial for maintaining cell integrity and function.
Osmotic Pressure: Osmotic pressure is the pressure that must be applied to a solution to prevent the flow of water molecules across a semipermeable membrane from a region of lower solute concentration (higher water concentration) to a region of higher solute concentration (lower water concentration). It is a crucial factor that affects the growth and survival of microorganisms in various environmental conditions.
Oxidation-Reduction Reactions: Oxidation-reduction reactions, also known as redox reactions, are a fundamental type of chemical reaction in which the oxidation state of atoms is changed. In these reactions, one substance loses electrons (is oxidized) while another substance gains electrons (is reduced), resulting in the transfer of electrons between chemical species.
Peptidoglycan: Peptidoglycan is a structural component found in the cell walls of most bacteria, providing them with shape, rigidity, and protection. It is a complex molecule composed of sugar and amino acid subunits that forms a mesh-like layer surrounding the bacterial cell membrane.
Photoautotrophs: Photoautotrophs are organisms that can synthesize their own organic compounds from inorganic carbon sources, such as carbon dioxide, using energy from sunlight through the process of photosynthesis. This ability to produce their own food from light energy and carbon dioxide is a key feature of photoautotrophs and connects them to the topics of energy, matter, and environmental conditions that affect growth.
Photoheterotrophs: Photoheterotrophs are a group of microorganisms that can use light energy to power their cellular processes, but they rely on organic compounds as their carbon and energy sources, rather than inorganic carbon sources like carbon dioxide. This unique metabolic strategy allows them to thrive in environments where light is available, but organic nutrients are limited.
Photosynthesis: Photosynthesis is the process by which certain organisms, such as plants and some bacteria, use the energy from sunlight to convert carbon dioxide and water into glucose and oxygen. This process is essential for the survival of many life forms on Earth, as it provides the primary source of energy and food for a vast array of organisms.
Photosynthesis is a crucial topic in the context of 4.3 Nonproteobacteria Gram-Negative Bacteria and Phototrophic Bacteria, 5.4 Algae, 8.6 Photosynthesis, and 9.5 Other Environmental Conditions that Affect Growth, as it is the fundamental process that powers the growth and development of these organisms.
Phototrophs: Phototrophs are organisms that obtain their energy through the process of photosynthesis, using light energy from the sun to convert carbon dioxide and water into organic compounds, such as glucose. These organisms are a crucial component of many ecosystems, serving as the primary producers that form the foundation of food webs.
Plasmolysis: Plasmolysis is the process in which cells lose water in a hypertonic solution, causing the cell membrane to pull away from the cell wall. This often leads to cellular dehydration and reduced metabolic activity.
Plasmolysis: Plasmolysis is the process in which the cell membrane of a plant cell or a bacterial cell pulls away from the cell wall due to the loss of water from the cell. This occurs when the cell is placed in a hypertonic environment, where the concentration of solutes outside the cell is higher than the concentration inside the cell.
Purple nonsulfur bacteria: Purple nonsulfur bacteria are a group of phototrophic bacteria capable of photosynthesis without producing oxygen. They can grow in the presence or absence of light and use organic compounds as electron donors.
Synechococcus: Synechococcus is a genus of unicellular, marine cyanobacteria that are important primary producers in the world's oceans. They are known for their ability to thrive in a variety of environmental conditions, making them a key component of 9.5 Other Environmental Conditions that Affect Growth.
Tonicity: Tonicity refers to the relative concentration of solutes on either side of a semipermeable membrane, which determines the direction and extent of water movement across the membrane. It is an important concept in the study of environmental conditions that affect microbial growth.
Turgor Pressure: Turgor pressure is the pressure exerted by the contents of a cell against the cell wall or cell membrane. It is an important factor that affects the growth and overall health of cells, particularly in plants and some microorganisms.
Water Activity: Water activity is a measure of the availability of water in a system, which is a critical factor in determining the growth and survival of microorganisms. It is a dimensionless quantity that ranges from 0 to 1, with 0 representing a completely dry environment and 1 representing pure water.
Water activity (aw): Water activity (aw) is a measure of the availability of water for microbial growth, represented on a scale from 0 to 1. It indicates how much water in a substance is free for microorganisms to use.