Notes:

We will end our discussion of applied microbiology with a brief summary of the importance of micro-organisms in agriculture. The process of breaking down carbohydrates under anaerobic conditions is called fermentation; and numerous microbes have been cultured (grown) to use in activities that yield desired by-products. The process of fermentation has been applied to disposal of sewage. From the outdoor privy(pit) and the more acceptable septic tank to public wastewater treatment plants, microbes have an important role in the decomposition of wastes. Also numerous microbes have been identified that will use various substrates and convert them into desirable human foods. Included in these useful microbes (products) are Saccharomyces (bread), Acetobacter (vinegar), Pediococcus (sausage), Lactobacillus (yogurt), Propionibacterium (Swiss cheese), Bacillus (cheddar cheese), Streptococcus (cottage cheese), and Penicillium (blue cheese). Additional yeasts and molds produce beverages like wines and beer (Saccharomyces) and rice wine (Aspergillus). Farmers (as well as urban dwellers) enjoy these foods and beverages. Accounts of Noach and others reveal that wine-making goes back to at least 3000 B.C.; and the production of beer from barley dates even earlier. It was not uncommon for early United States colonists to ferment pumpkins, corn, and potatoes into beer.

One of the oldest methods of preserving animal food is the fermentation of hay, cereals, grass, or other vegetation in a silo. This combination of vegetative material that has been preserved by anaerobic fermentation is called silage. Naturally occurring bacteria like Lactobacillus on the plants will ferment the carbohydrates and release acids that inhibit growth of spoilage microbes and also release gasses giving silage its smell. Other soil microbes including Clostridium will alter the fermentation process and reduce the palatability of the silage. Microbes like Clostridium should not be permitted to contaminate the plants used in making silage.

Animals like cattle, sheep, goats, and deer are called ruminants; and these animals have an interesting relationship with microbes. Ruminants eat a great amount of coarse plants and do not chew the vegetation very much. The food is stored in a large fermentation chamber of the stomach called the rumen. Bacteria, protozoans, and yeasts in the rumen secrete enzymes that digest the cellulose. Undigested food may be formed into a “cud” and brought back up for additional chewing. The protozoans in the ruminant’s stomach are primarily ciliates; and the bacteria are bacilli and cocci. The cocci are most numerous when grains are the primary food of the ruminant; and bacilli are most numerous in the digestion of roughages.

Soil is the loose material on the earth’s surface; and microbes are very numerous. The weight of soil organisms may range from 4025 to 6250 pounds per acre-foot. Bacteria are the most numerous microbes in the soil; and Arthrobacter is probably the most common soil bacterium. Other bacteria in the soil include Pseudomonas, Bacillus, Flavobacterium, Micrococcus, Sarcina, Nitrobacter, and Thiobacillus. Other common microbes in the soil include actinomycetes including Streptomyces and Nocardia which give the “fresh smell” to spring soil and other common microbes are the molds like Mucor, Aspergillus, and Penicillium. Mucor has been identified as one of the important microbes in the decomposition of dung (feces). Microbes are essential in the soil for releasing nutrients and decomposition of organic material. Other microbes like Azotobacter and Rhizobium fix nitrogen. Rhizobium is found primarily in nodules (swellings) on the roots of legumes like peas, beans, clovers, and alfalfa. Spores from Penicillium and other molds are sometimes inoculated on seeds prior to planting. This fungal growth produces antibiotics which inhibit the bacterial growth which might attack the seeds.

Farmers must dispose all excess plant and animal debris properly. Through incineration (cremation), burial, and recycling the farmers eleiminate the extra debris. Rendering services collect large dead animals and process them. Many plants and animals (including the agricultural workers) are donated to science for study. These organisms must be preserved (anatomically embalmed); and the surface is cleaned with ammonium chloride. Internal preservation of the animals is completed by replacing the tissues like blood with formalin. This preservation prevents decomposition by anaerobic acidophiles like E.coli and Clostridium and protects the handlers from viruses such as hepatitis and HIV.

Farmers also need to control parasite infestations. Worms like nematodes (Ascaris) and flatworms (Taenia-- tapeworm, Clonorchis and Fasciola --flukes) as well as arthropods cause great economic loss to farmers. Spider mites, aphids, termites, ticks, fleas, and lice are some of the damaging arthropods. In addition to reducing the yield and production, some of the arthropods are the vectors of pathogenic microbes.

Many plants and animals are susceptible to pathogenic bacteria, fungi, and viruses. Superficial (surface) and internal infections are caused by the pathogens. Since many pathogens are found in the soil, it is impossible to eliminate all the pathogens; and special care and treatment will always be needed. By isolation, protection, selective breeding, and other techniques the incidence and spread of microbes can be minimized. Bacteria that attack plants include Erwinia (rots), Pseudomonas, Xanthomonas, and Agrobacterium (galls). Fungi that damage plants include Puccinia (rusts), Ustilago (smuts), Phytopththora (blights), Pythium (damping off), Claviceps (blight), and Fusarium (scab). Curly beet top, mosaic diseases, and stunt diseases are often caused by viruses. Among the important animal pathogens are bacteria like Bacillus (anthrax), Brucella (brucellosis), Salmonella (hog cholera), Mycobacterium (TB), Clostridium (foot rots), Haemophilus (colds), and microbes like Staphylococcus, Streptococcus, E.coli, and Klebsiella which cause mastitis. Ringworm is a fungal disease of animals; and Aspergillus may cause farmer’s lung. Rabies, encephalitis, and foot-and-mouth disease are three viral diseases of animals. Coccidiosis is a protozoal disease of young animals caused by Eimeria. Plants and animals may appear diseased and show reduced production as a result of injury, lack of nutrients, and reproductive stress so always “keep an close eye” on your crops and livestock.