Microbiology - all about Microorganisms

Microorganisms as bio control agents in agriculture

Piyumalie Lakma Hettiarachchi
Third Year, Faculty of Science, University of Colombo

In Sri Lankan agriculture industry the most outstanding and most troubleshooting problem is the supplement of sufficient amount of crop yield according to the customer’s need. The higher increment of the price in the market for some crop cultivators is caused by the increasing population and the lack of the supplement that the market needed.

Some of the problems that can be said as causes for this issue are natural disasters that destroy the cultivated crops during the seasons, insects’ damage, storage problems, transportation problems, lack of nutrients, lack of relevant equipment and resources etc. Many European countries who cultivate certain crop items in large-scales, have the major problem of the crops being attacked by several pathogenic microorganisms which lead to severe diseases to the plants. So they have the technology and research knowledge on overcoming pest’s damage using “microorganisms” as bio control agents.

Biological control is a method of controlling pests such as insects, mites, weeds and other plant diseases using other organisms. This method can be improved as an important role in integrated pest management. So using friendly microorganisms, these pathogenic microorganisms and the diseases can be maintained and managed. There are so many studies and researches which are based on testing the potential of the microorganisms which can be used as bio control agents, exploring their properties against fungi or bacterial activity and their ability to boost plant defense mechanisms.

For example, Micromonosporasp is a bacterium which can be used against the fungi Botrytiscinerea, which cause the gray mold in “Tomato”. Actually, this necrotrophic pathogen also causes the softening in fruits and gray mold in many vegetables, which leads to the removal of tremendous amount from the cultivated crop yields from the market. This Micromonosporasp induces the systemic resistance in tomato plant against the Botrytiscinerea’s activity. This bacterium can be used in reducing the negative effect of pathogens in plant, inhibiting pathogen growth by production of antibiotics, lytic enzymes or siderphores or induce plant defense mechanisms.

By introducing this Micromonosporasp in to the soil near to the roots or in to the leaves of the tomato plant it, induces the “Jasmonate Acid” regulated responses, which is a natural defense mechanism that occurs on plant at the presence of the pathogen fungi. The most interesting consequence is that this Micromonospora sp. (bacteria) would not harm the Tomato plant at the absence of the pathogenic fungi. So without any chemical interference, the pest can be controlled easily. So this method is a much healthier and ecofriendly manner in pest and disease control.

In the present, Sri Lanka is also trying this technology on “Tea”. The scientists have been shown the antagonistic fungi and bacteria that parasitize pathogenic fungi and destroy the pathogen in one of several ways. This effectively increases the crop yield at the harvesting mechanism, which improves the quality of the final product. It’s very important to enhance the quality as well as the final crop yield of the “Tea”, as it is one of the main export crops to the international market from Sri Lanka. So by using these microorganism intended technology, it easily reduces the huge monetary expenses on pests’ eradication. So it’s cost effective.

Practically it acquired huge chemical amounts to use in a large scale cultivated crop types to control the pathogenic microorganisms.So the bioaccumulation of certain chemicals on the environment is also increased and finally it would be toxic to the humans and environment too. It needs only few amount of fractionating friendly microorganisms instead of huge amount of chemicals for the process.It protects the biodiversity and natural enemies of the pest.

But the huge usage of the microorganisms without a control would lead to the appearance of new species. This disrupts the balance of the natural ecosystem and pesticides would bio accumulate in food chains. If the microorganisms are controlled well, this method would be the best in pest control and disease control of crop plants in a country like Sri Lanka.

Importance of bacteria

Kalhari Ashinsa
Third Year, Faculty of Science, University of Colombo

Bacteria live almost anywhere imaginable from inside your intestines to the bottom of the ocean floor. In fact, bacteria are beneficial to humans in pharmaceutical industry, biotechnology, food industry, agriculture, ecologically, and other human activities.

Today, biotechnology shows a massive development. They use microorganisms such as bacteria to develop new drugs and vaccines. Antibiotics such as Erythromycin, Streptomycin, Vancomycin, Bacitracin are developing from biotechnology using different bacterial varieties. Vaccines like tetanus are made by inactivating the tetanus toxin of bacteria clostridium tetani.

Recombinant DNA technology has developed to produce teneticall modified organisms which

has desired characteristics such as resistance varieties to harmful agents, enhance food resources, produce valuable proteins like insulin and so on. Bacterial plasmids are used to produce transgenic organisms which has modified gene structure. Gene structure is modified by inserting new genes to bacterial plasmids. Bacterial plasmids act as vectors due to their faster growth rate, easy cultivation and handling.

Bioremediation uses naturally occurring bacteria to degrade or detoxify substances hazardous to human health and/or the environment. Bacteria utilize chemical contaminant as an energy source and through oxidation-reduction reactions, metabolize the target contaminant into usable energy forms for microbial metabolism. Byproducts of this metabolism are released back into the environment which are typically in a non or less toxic form than the parent contaminant.

Some of the bacteria are used as bio indicators. Especially Coliform bacteria such as Escherichia coli, pseudomonas, Enterobacter are used to monitoring water quality to identify fecal contamination of drinking water. Those indicator bacteria are not harmful to human health but are useful to risk identification.

When considering the bacterial effect in food industry, main issue of bacteria is food spoilage. But bacteria play an important role in food industry specially in dairy products and fermented food production. Fermentation of food increase self-life and add desirable flavors to it. Yoghurt is a commonly used from of fermented milk. Lactobacillus bulgaricus and Streptococcus thermophiles are used to produce acidity and desirable flavor of yoghurt. Cheese production involves lactic acid fermentation. This process has done by lactic acid fermented bacteria like Lactococcuslactis and Lactococcuscremosis. Countries like Japan and China consume number of fermented meat and fish products which are fermented using bacteria such as Pediococcus, Lactobacillus.

In agriculture, saprophytic and symbiotic bacteria add to the soil to improve soil fertility and provide nitrogen to the plants. Bacteria like Rhzobium, Nitrobacter, Azotobacter, Nitrosomonas involve in N cycle. They fix atmospheric N in the form of nitrogenous compounds in the soil. Then, plant can easily obtain those compounds for their growth.

So, according to above facts it can be concluded that there are lots of advantages from bacteria in different fields and only a small fraction cause food spoilage and diseases.

Microbial effects of food spoilage

L.T.C. Sewwandi 
Third Year, Faculty of Science, University of Colombo

Food spoilage can be described as the process by which food quality becomes compromised and its edibility significantly reduced. It is the process leading to a product becoming either undesirable or unacceptable for human consumption.

Numerous signs are indicative of food spoilage and they range from changes in the ordinary appearance of the foods, changes in its texture, bad odour and poor taste. Microbiological food spoilage is caused by the growth of microorganisms which produce enzymes that lead to objectionable byproducts in the food. Bacteria, yeasts and molds are microorganisms that cause food spoilage. They produce various enzymes that decompose the various constituents of food.

Molds are the major causes of spoilage of foods with reduced water activity such as dry cereals and cereal products. Bacteria spoil food with relatively high water activity such as milk and milk products. The primary sources of microorganisms in food include; soil and water, plant and plant product, food utensils, intestinal tract of man and animals, food handlers, animal hides and skins, air and dust.

There are two types of factors that affect microbial growth food. They are intrinsic factors and extrinsic factors. Intrinsic factors are inherent in the food. They include pH, moisture content, nutrient content of food, antimicrobial substances and biological structure of foods. Yeasts and molds grow under acid conditions. Other microorganisms such as Vibrio cholera are sensitive to acids and prefer alkaline conditions.

Most bacteria are killed in strong acid or strong alkaline environment except Mycobacteria. Moisture content is also important for growth of microorganisms. If there is lack of free water, microorganisms will not grow. Salting and drying reduces the water activity of a food product.

Nutrient content of the food also affect the microorganism growth. Microorganisms require proteins, carbohydrates, lipids, water, energy, nitrogen, sulphur, phosphorus, vitamins, and mineral for growth. Various foods have specific nutrients that help in microbial growth. These foods are hence susceptible to microbial spoilage. Antimicrobial substances in food inhibit microbial growth. Various foods have inherent antimicrobial substances that prevent microbial attack. Such inhibitors are like actinin and anticoliform factors in milk and lysozyme in eggs.

Some foods have bilogical structures that prevent microbial entry. For example, meat has fascia, skin and other membranes that prevent microbial entry. Eggs have shell and inner membranes that prevent yolk and egg white from infection.

Extrinsic factors are factors external to the food that effect microbial growth. They include temperature of storage, presence and concentration of gases in the environment, relative humidity of food storage environment. The effect of temperature on microbial growth also depends upon other environmental conditions such as growth factors in the nutrient medium, pH of the food and water activity.

Concentration of gases in the food environment also affect to the microbial growth. Anaerobic or facultative anaerobic spore forms are most likely for growth in canned foods. Microaerophilic bacteria are most likely to grow in vacuum packed foods since they have low oxygen tension. Aerobic bacteria are likely to grow on the surface of raw meat. Aerobic molds will grow in insufficiently dried or salted products. Relative humidity is the amount of moisture in the atmosphere or food environment. Foods with low water activity placed at high humidity environment take up water, increase their water activity and get spoiled easily. Food preservation is a process through which physical and chemical agents are used to prevent microbial spoilage of food.

Food preservation aims at treating food in a manner to prolong its storage life.

There are two general principles that are employed in food preservation. They are inhibition and killing. In the inhibition principles, food preservation is achieved by inhibition of growth and multiplication of microogranisms. It is achieved by reduction of water activity by drying or salting. Reduction in pH is achieved by fermentation and addition of acids, use of preservatives such as sodium benzoate, use of low temperature by chilling or freezing and smoking.

In the killing principle, spoilage microogranisms are destroyed in the food, and the food protected against subsequent contamination by being enclosed in an air tight container. In this principle, food preservation is achieved by treatment through pasteurization or sterilization, irradiation and use of gases such as ethylene oxide or ozone.