Question

1. What is habitat and metabolism type for borrelia burgdorferi?

2. What is the human and or ecological relevance for helicobacter pylori and its metabolism type?

3. What is the metabolism type for methanogens and the human relevance?

Answer 1

1.

The Lyme disease is caused by Borrelia burgdorferi and other species include B. garinii and B. afzelii. The deer and field mice are natural hosts of these spirochetes. The B. burgdorferi is a microaerobic, motile spirochete with seven to 11 bundled perisplasmic flagella. It is a slow-growing microaerophilic spirochete having doubling time of 24 to 48 hours.

The Borrelia burgdorferi is transmitted to humans by the bite of infected deer tick called Ixodes scaplularis. The Lyme disease progresses with three major stages. The initial and localized stage begins after infectious tick bite. The illness is characterized by appearance of an expanding and ring shaped skin lesion with red outer border and central clearing. It is known as erythema migrans and other symptoms include malaise, fatigue, headache, fever and chills.

The tick bite is unnoticed and skin lesion is usually missed due to its coloration. The treatment is effective only at this stage and it is assumed as simple flu and untreated mostly. The second stage is characterized by dissemination appearing after weeks to months of initial infection. It is characterized by neurological abnormalities, heart inflammation and bouts of arthritis. The inflammation of organs results in damage and can be increased by immune response to the spirochete proteins.

The final stage is like progression of syphilis and appear years later. Infected individuals may develop neuron demyelination and Alzheimer’s disease and multiple sclerosis. The initial diagnosis is important and treated with amoxicillin and tetracycline.

2.

The human pathogen Helicobacter pylori is responsible to cause gastritis and peptic ulcer disease. Along with the peptic ulcers, the infection of H. pylori has a strong correlation with gastric cancer. The H. pylori colonize the gastric mucus – secreting cells alone under the gastric mucous layers.

It contains the surface fimbriae that act as adhesins enable binding with mucous layer. The H. pylori also binds with surfaces of several cells. These include Lewis B antigen, blood group antigens that determine the blood group O and monosaccharide sialic acid, glycoproteins found on the surface of gastric epithelial cells. Further, the bacteria move into mucous layer attaching to mucous secreting cells. This can be enabled by production of urease by H. pylori.

The secretion of urease helps in creation of local alkaline environment by hydrolysis of urea to ammonia. This neutralizes the gastric acid and also increases the pH of stomach to protect the bacterium from the gastric acid. Thus, it is able to grow invading into the layer of mucus. It possesses virulent factors such as proteases, phospholipases and cytotoxins that cause damage to the epithelial cells and inflammation.

3.

The methanogens belong to the phylum Euryarchaeota composed of many genera. The methanogens are strict anaerobes and depend on substances like CO2, H2, formate, methanol, acetate and other compounds as source of energy. They can also use methane or methane and CO2. These are autotrophs that grow on H2 and CO2 and can form acetyl CoA from two molecules of CO2. Further they convert the acetyl CoA to pyruvate and other products. Since, the methanogens are anaerobic they are abundantly found in sewage sludge and produces methane. The methane is the biogas produced from animal, humans and other kind wastes and produced by the process of anaerobic digestion. The rumen methanogens are active and a cow can produce 200 to 400 liters of methane due to methenogenic metabolism. The methane is a clean burning fuel and very good energy source. The microbes within the anaerobic digester degrade the particulate waste and sewage sludge into H2, CO2 and acetate.