KINGDOM MONERA

MEMBERS of Kingdom Monera, commonly known as bacteria, are unicellular. They have no distinct nucleus and can survive in the presence (aerobic) or absence of oxygen (anaerobic). While some bacteria are autotrophs and can make their own food by photosynthesis, the majority are heterotrophic in nature and so cannot make their own food — they may be parasitic and feed off a living host or saprophytic and live off dead or decaying organic matter.

STRUCTURE: Bacteria are either spherical in shape (Cocci), rod-shaped (Bacillus) or spiral in shape (Spirillum). The structure of a typical bacterial cell can be seen in Fig.2

REPRODUCTION: Bacteria reproduce asexually by a process known as binary fission which can result in the production of several generations over a couple of hours. Bacteria have the ability to form endospores if conditions are unfavorable — structures which allow them to survive in harsh conditions. SIGNIFICANCE IN AGRICULTURE Beneficial Effects:

A bacterium in the soil, known as Rhizobium, are responsible for ‘nitrogen-fixation’ — the process whereby atmospheric nitrogen is converted into nitrates, which plants can use. Rhizobium forms a symbiotic relationship with the root nodules of the clover plant. Symbiosis is when two or more organisms of different species live in or on another organism and at least one benefit.

Herbivores such as cattle and sheep have bacteria in the rumen, the largest compartment in the ruminant stomach, which aid in the digestion of cellulose. The cattle and sheep provide a suitable environment in the form of the rumen in which the bacteria thrive, thus demonstrating a second example of a symbiotic relationship. The bacteria which help to digest cellulose in herbivores without a rumen such as horses and rabbits are present in the large intestine. In addition, bacteria help to synthesise vitamins B and K in some mammals, including humans.

Milk is modified by the action of bacteria to produce cheese, yoghurt and buttermilk.

Fermentation is the process by which silage is produced and de-

pends on the presence of desirable bacteria such as Lactobacillus and Streptococcus. Harmful Effects

DISEASE:

Many diseases in mammals are caused by bacteria. These include pneumonia, navel/joint ill, mastitis and tuberculosis. The modes of transmission for bacteria vary from air to water to food.

Both bacterial scour and coliform scour are as a result of poor management and lack of hygiene on the farm. In some cases, bacterial diseases may be either spread by blood-sucking parasites, or the presence of parasites may increase the incidence of bacterial disease. For example, liver-fluke may increase the susceptibility of the host animal to Salmonellosis, a bacterial infection.

In addition, bacteria are responsible for many diseases in plants such as blackleg and common scab, which affect potatoes. The presences of bacteria in plants can result in galls or swollen tissues, cankers which cause tissue decay, and wilts which block the xylem vessels. Economic Loss

On the dairy farm, bacteria pose a threat to both the health of the animal in causing mastitis and to the profit margins because of the resulting decrease in milk yields. In addition, the bacterium Lactobacillus causes milk to go sour, which can again result in financial loss for the farmer.

An undesirable organism known as Clostridium can result in a poor quality silage, slimy in texture with a rancid smell. This may warrant for the use of concentrates on the farm to supplement the poor quality silage, increasing costs once again.

Bacteria may be responsible for the rotting of crops during storage and certain procedures such as the acid treatment of barley are undertaken to prevent against bacterial disease during crop storage.