Bread-making uses yeast fungi. When the yeast is provided with sugars, fermentation occurs, breaking down sugar to produce carbon dioxide. The release of CO2 makes the bread rise and results in the holes found in bread. Alcohol is also produced during fermentation, but evaporates when bread is cooked.
Lactic acid bacteria are used in a number of methods of food production, including cheese making (lactococcus) and yogurt (lactobacillus). Cheese making involves the acidification, coagulation, dehydration and salting. During acidification the lactic acid bacteria are added to milk as a starter culture. The lactic acid they produce give cheese an acidic flavour and coagulate casein protein. The bacteria also release enzymes that ripen cheese and produce antibacterial substances that slow growth of pathogens allowing longer storage.
In yogurt production the lactic acid lowers pH of milk to 4, gives yogurt its tangy taste, changes texture of milk and inhibits spoilage allowing longer storage.
When food spoils, it becomes hard to eat because of the change in texture, colour, smell or taste. These changes occur because of the effect of enzymes on carbohydrates, proteins and fats. Preserving methods avoid this eg in jam fruit is boiled in a sugar until water has evaporated and jam is set in gel. boiling kills all the micro-organisms in on the fruit and sealing in jam stops spoilage by micro-organisms. However high moisture means mould can grow when jam is opened.
All methods of food preservation are made to produce an environment free of micro-organisms or one that makes them unable to grow and reproduce examples:
Refrigeration - temperature below 4 degrees slow growth of micro-organism eg milk
Freezing - temperature even lower than fridge increases storage time by stopping growth and reproduction eg meat
Salting- salt removes water from bacteria and fungi, stops growth eg bacon
acidificaton- lactic acid lowers PH slows growth of spoilage micro-organisms eg yogurt
drying - remove water to stops growth eg garlic
freeze-drying freezing, removal of water and sealing increases storage time
canning - cooking kills micro-organisms and sealing prevents them entering again eg peaches
heating denatures the enzymes and proteins in cell membrane so cells cant carry out life processes like respiration, digestion and reproduction. The sealed can and lid stops oxygen from entering food, stopping respiration, so they are unable to produce energy.
If can is opened, micro-organisms can enter food again, growing reproducing and making toxins that make food unsafe to eat. oxygen in the air enable aerobic micro-organisms to carry out respiration. Putting can in the fridge can slow growth and reproduction as the cold slows chemical reactions.
Sewage treatment
sewage is wastewater and solid material from bathroom, toilet, kitchen, laundries, and industrial wastewater. The feeding and respiration of micro-organisms breaks down the organic material in sewage. Liquid and solid parts of sewage are separated - aerobic bacteria feed on the liquid part of sewage, breaking it down to release nutrients. Anaerobic bacteria, which produce methane gas, break down the solid parts of sewage.
Bacteria in the aeration tank are saprotrophs that decompose organic material in sewage, breaking it into carbon dioxide, water, nutrients and minerals that can be used by bacteria and plants. First bacteria carry our extracellular digestion and some of the digested material is used for respiration to make energy needed for growth and reproduction. Oxygen is added to tanks to ensure aerobic bacteria can carry out aerobic respiration and remain active.
Sewage treatment is important as it removes pathogenic micro-organisms and organic material so the liquid can be released into waterways and not cause disease or nutrient overloading.
producing antibiotics
penicillin was the first antibiotic produced and used to treat bacterial infections. It is now produced in large amounts by fermentation from mould or synthetically.
Antibiotics upset the reproduction, feeding, growth and metabolism of bacterial cells. different antibiotics affect different life processes. For example antibiotic that damages DNA stops protein being made and so stops growth and reproduction of bacterium.
diagram:
Antibiotics work by upsetting the function of cells like bacteria and fungi eg damage cell membrane. Antibiotics don't work against viruses as they are not cells, do not have parts like cell membranes and do not carry out most life processes eg respiration
Vaccine delivery
A vaccine can be injected to give an organism immunity to a disease. research is being done to develop vaccine delivery systems using lactococcus bacteria. The bacteria is genetically modified so it has protein on its surface that are the same as those carried on a pathogenic species eg lactococcus can be modified to produce proteins the same as streptococcus that causes strep throat. When the modified lactococcus is sprayed into the nose, it causes an immune response to the pathogens proteins, which gives future immunity to streptococcus
Genetic mutation in epidemiology
epidemiology is the study of patterns of disease. Patterns of disease have been studied through the identification of mutations in genes carried by micro-organisms. For example, investigation of mutations in the bacteria Bacillus anthracis (anthrax) has allowed specific strains of the pathogen to be identified and this information used in epidemiology. eg a anthrax outbreak in South africa was shown to caused by a rare strain of anthrax found in soil. In another case, a death by anthrax was found to be from a laboratory strain and was found to be murder.
In epidemiology of breast and other cancers, genetically modified (GM) bacteria are used to study the effect of genetic mutation in different genes eg tumour suppressor genes. Different mutations cause different changes in the protein produced as a result of the gene. Using GM bacteria lets researchers investigate the specific change that different mutations have on the resulting protein and consider the effect this has on a person with the mutation.
Harmful effects on micro-organisms
food poisoning
disease
microbial attack on material
antibiotic resistance
Food poisoning
food poisoning is any illness caused by eating food contaminated by bacteria or their toxins. This is common in summer months when warm temperature speed up bacterial growth and reproduction in food. food left out of fridge for a long time can contain enough bacteria and toxin to cause diarrhoea, stomach cramps, nausea, and vomiting when eaten. The symptoms are most commonly caused by campylobacter, salmonella, e coli, staphylococcus aureus, listeria and clostridium botulinum
Food poisoning from campylobacter and salmonella commonly occurs when people eat undercooked or unrefrigerated chicken containing large numbers of bacteria. S. aureus results in toxins n food such as cold meats, custards, salads and baked foods especially if the food handler had a skin infection of S. aureus.
Diseases
plant disease
The moist, temperate climate of New Zealand, where temperature and rainfall don't vary much, is ideal for growth and reproduction of disease-causing fungi and bacteria. The climate also suits insects that transport plant viruses.
Most plant diseases are caused by fungi, eg black spot, rusts, grey mould and mildew. Grey mould occurs in glass houses and infects leaves, stems, flowers and fruit of a range of different plants. Brown spots and dying plant parts are common signs. When temperatures are between 15-25 degrees or humidity is high, spores from fungus germinate, grow quickly and new fungi produce many spores. good airflow and low humidity can control outbreak of disease.
Powdery mildew disease is caused by a fungus and occurs in plants in dry conditions, such as cucumber plants. Spores contain 70% water so they dont need water to germinate. once germinated, fungus absorbs water from leaves of host plant, applying water and creating conditions of high humidity can control this disease.
Bacterial plant disease is not as common as fungal diseases but can cause much damage. eg psa attacks golden kiwi fruit plants. This disease causes brown spots, causing leaves to fall off and killing the kiwi fruit vine. 2010 outbreak was caused by unusually wet warm spring, which is ideal conditions for bacteria.
Disease in humans and other animals
Pathogenic micro-organisms cause a range of disease in humans and other animals because warm, moist bodies of humans and animals provide food and excellent conditions for the growth and reproduction. Each pathogen has its own environmental condition eg tinea occurs outside the body where skin cells become food while thrush grows inside the mouth where temperature and moisture levels are higher.
Microbial attack on material
Bacteria and spores from bacteria and fungi can grow on everyday objects made from plant and animal material like wood, cotton, leather and wool. Bacteria feed on these by extra-cellular digestion, the enzymes released breaks down the material. eg brown-rot fungus attacks wood reduces its strength.
Antibiotic resistance
In any population of living organisms, there is natural variation. This means that some bacteria in a population may carry alleles that give them resistance to an antibiotic. The bacteria carrying allele for resistance are not killed by the antibiotic so they reproduce making more bacteria resistant to that antibiotic. Over time the entire bacterial population becomes resistant to antibiotic meaning another antibiotic is needed. Extensive use of antibiotics causes more anti-biotic strains of bacteria. Unnecessary prescibing of antibotics increases exposure of a large range of micro-organisms to antibiotics, causing the development of resistant bacteria.