Microbial nutrition is essential in the survival and growth of microorganisms. Talaro and Chess considers several factors which are key players in the survivability of microbes in order to adapt or “inhabit all parts of the biosphere.” Among these factors include nutrients, temperature, pH, water availability, atmospheric gases, light, pressure and other organisms inhabiting the earth. Nutrition in essence is that which chemical substance in the form of nutrients are ingested inside the body such that when assimilated leads to the formation of energy to be used for metabolic activities.
Organisms require organic forming compound elements such as carbon, hydrogen, nitrogen, oxygen, phosphorus, sulphur and ions such as sodium, chloride, potassium, calcium, iron, and magnesium for survival. Essential nutrients needed by a body in large quantities are called macronutrients while micronutrients are required in smaller amounts (i.e. trace elements such as zinc, manganese and copper). Aside from nutrients being classified based on the amount required to push for metabolic activities, nutrients are also categorized as organic and inorganic. Organic nutrients are those of carbohydrates, fats and proteins while inorganic nutrients are those minerals found in small quantities.
An organic nutrient that cannot be synthesized is called a growth factor and this is in the form of amino acids and vitamins. These growth factors must be provided and must come from other sources such as plants for instance. Autotrophs like plants are the only organism capable of synthesizing their own food. It depends on carbon dioxide for its carbon requisites and it harnesses energy from light. A on the other hand, chemoautotroph extracts energy from inorganic substances. An example of a chemoautotroph is a methanogen which upon metabolic activity synthesizes methane as a by-product. Heterotrophs cannot synthesize their own food as opposed to autotrophs. Thus carbon is taken from another source (i.e. from organic molecules). Best example to illustrate heterotrophs would be a saprobe which feeds upon dead organic matter and parasites from a live host. As a result a saprobe can be detrimental to a live host. Pathogens are those parasites that can cause damage and death generally.
Part of understanding nutrition is taking a look at how nutrients are transported to the body. It is common knowledge that a microbial cell must take in nutrients from its surrounding by means of transporting these nutrients across the cell membrane. The most common type of movement across the cell membrane is called osmosis. Osmosis is the movement or diffusion of water in a semipermeable membrane from a higher concentration to a lower concentration. Changes in osmosis can affect the cells shape and integrity. Among the types of osmotic changes which affects the cell include hypotonic solutions (i.e. having a lower solute concentration), and hypertonic solutions (i.e. having higher solute concentration). Isotonic solutions, from the word “iso” meaning equal, imply that solutions have the same solute concentration inside and outside of the cell. Microorganisms associated with hypertonic environment include halophiles. Halophiles grow in hypertonic conditions while an obligate halophile requires a salt concentration of at least 15% but grows best at 25% salt concentration.
There are two types of transport mechanism in the natural environment which affects the physiology of microoganisms. That is, the passive transport and the active transport. In passive transport, no additional energy is required when substances move across the cell membrane via diffusion. For instance the movement of water inside the membrane is a type of passive transport called facilitated diffusion. Other specific substance also moves inside the membrane via facilitated diffusion. As opposed to passive transport, active transport requires energy, when substances are taken into a cell through a particular process such as in group translocation. During such process, molecules are transformed during movement which requires a toll of energy. Two forms of active transport are called phagocytosis and pinocytosis. In phagocytosis large amounts of solid material are engulfed. Phagocytosis is also called “cell-eating.” Pinocytosis which is also known as “cell drinking,” fluid materials are engulfed inside the cell.
It is a general knowledge that organisms must undergo an adaptive strategy to find a suitable habitat and established and ecological niche. As previously mentioned there are various factors affecting the survival of an organism and its interplay to its environment. Among these factors are: temperature, gas in the atmosphere particularly oxygen requirement, pH and other factors such as radiation and barometric pressure.
Temperature is a limiting factor which allows an organism to survive at a given range of tolerance. Organisms display an optimum, minimum and maximum temperatures. Microorganisms are associated with the level of temperature in which they can thrive. To elaborate further, psychrophiles are organisms that cannot tolerate temperature above above 20°C but can still survive below 15°C and even at 0°C. Mesophilic organisms can grow at a range of 10°C to 50°C, but the optimal temperature for growth ranges from 20°C to 40°C. Thermophiles however can only tolerate temperatures at 45°C to 80°C. Yet those extreme thermophiles are capable to adapt to temperatures of 250°C.
The common need for free oxygen (O2) is based on the principle of the cell’s capacity to handle toxicity such as peroxides. Aside from temperature tolerance, the classification of microorganism further extends to oxygen-requirements. Aerobes are those that thrive in normal atmospheric oxygen. They contain enzymes which are capable of degrading harmful oxygen by-products. Anaerobes are those that can survive without oxygen or with a very small amount of oxygen. Those which do not require oxygen at all are called facultative anaerobles while those that needs a small amount of oxygen but do not thrive under anaerobic surroundings are called microaerophile. Strict or obligate anaerobes are usually damaged or killed by oxygen because they do not have the enzyme to catalyzed reactive oxides. Aerotolerant anaerobes are not injured when exposed to oxygen but they do not utilize this gas for respiration.
The acidity and alkalinity of the environment is measured by means of pH. Enzymes are basically pH sensitive and their functionality to catalyzed metabolic reactions is generally affected by fluctuations in pH. For most microbes the optimum pH is from 6 to 8. Microbes such as acidophiles prefer a pH below 7 hence the word acid while alkalinophiles prefer pH above 7 and neutrophiles apparently thrive most at pH 7. Other environmental factors such as radiation and barometric pressure can also significantly affect microbial growth. Organisms known as barophiles are well-adjusted to high pressure (i.e. bottom dwellers in the ocean).
Microorganisms co-exist in various interplays in nature in different types. A symbiotic relationship in microbes may be mutualistic, where there is reciprocity in two organisms. That is both organisms benefit from each other. In a commensal interrelationship, one organism benefits from the other while the other organism remains unharmed (i.e. one form is known as satellitism). In parasitism there is a host and an infectious agent. Parasites benefit while the host is harmed during the interplay. Other types of interaction also include synergism. In synergism, there is a mutual benefit between organisms but the coexistence is not necessarily obligatory. There is cooperation in organisms towards the production of a reaction. Antagonism on the other hand involves competition, inhibition, and injury toward the opposing organism such as in production of antibiotic to fight inflammation. In quorum sensing, there is a coordinated reaction among members of a biofilm. Biofilms are stable and organized when they act as a unit. Through the unit can colonized and exploit a wide range of habitat.
Understanding the processes involved on how microbes multiply is an important aspect in understanding microbial growth. Bacterial cells multiply by means of binary fission or transverse fission. In binary fission parent bacterial cell divides to form two daughter cells of the same size and genetic component. The period where cells divide is called generation or doubling time. Theoretically, the growth rate of the population is exponential in nature where an increase in geometric progression may be noted in each cycle given that a population doubles per generation. Using a growth curve one can make a graphical model representing how the population moves over time. In this model one can plot and estimate viable counts of live cells. There are two notable periods in the graphical model of a growth curve. The lag phase is the initial fl at the period of the curved and the exponential growth phase is the increasing viable cells in the logarithmic model. In this logarithmic model, several factors are accounted to explain the inhibition of growth rate in organisms leading to what is called a plateau or a stationary growth phase. During nutrient depletion and waste build-up, and increase in cell death follows which is also known as the death phase. Aside from modeling, there are numerous ways to count cell numbers. These include, a viable plate count, microscope counting chamber, Coulter counter, flow cytometer and other methods. Further, cell growth can also be established by way of turbidometry and cell count.
Talaro, Kathleen P. and Barry Chess. Foundations in Microbiology. New York: McGraw-Hill Companies, Inc., 2012. Print.