Bacterial Diversity of Selected Genuses - Class notes

Chapter 3 Gram negative aerobic rods and cocci(Pseudomonas Xanthomonas Neisseria)

1. Pseudomonas
2. Xanthomonas
3. Neisseria

 

Pseudomonas

Domain:      Bacteria

Phylum:      Proteobacteria

Class:           Gammaproteobacteria

Order:         Pseudomonadales

Family:       Pseudomonadaceae

Genus:        Pseudomonas

Habitat

• Pseudomonas is a genus of truly ubiquitous organisms
• Pseudomonas bacteria can be found in many different environments such as soil, water, and plant and animal tissue.
• Pseudomonas species are generally found in soils and water environments that have aerobic, mesophilic and neutral pH conditions.

Morphology

• Gram negative.
• All the genera in this group are straight or slightly curved.
• Straight or slightly curved rods but not helical, 0.5–1.0 μm in diameter by 1.5- 5.0 μm in length.
• That occurs singly or in pairs or short chains.
• Most of the species do not accumulate granules of poly-β-hydroxybutyrate.
• They have multiple polar flagella that assist in the bacteria's movement.
• Endospores formation occurs in some species, but infrequently

Physiology

• These bacteria are generally obligate aerobes.
• Pyocyanin production; growth at up to 43°C.
• Temperature range of 4–42°C. Species of Pseudomonas grow well at 28–30°C.
• pH between 4 and 8.
• Pigments produced by species of Pseudomonas include pyocyanin ( aeruginosa, blue color), pyorubin (P. aeruginosa, red color), oxychlororaphin (P. aureofaciens, orange color), chlororaphin (P. chlororaphis, green color), oxychlororaphin (P. chlororaphis, orange color), etc.

Growth & Nutrition

• Chemoorganotrophic
• Some strains can utilize NO3instead of O2as an electron acceptor.
• Because they have simple nutritional requirements, they "grow well in mineral salts media supplemented with any of a large number of carbon sources" 
• Pseudomonas typically has very simple nutritional requirements and one of their characteristic properties is the ability to use many different organic compounds as carbon and energy sources.
• Most Pseudomonas species grow in chemically defined media without added growth factors.
• Some species utilize over 100 different compounds.
• The Pseudomonas are ecologically important in soil and water and are probably responsible for the degradation of many low-molecular-weight compounds derived from the breakdown of plant and animal materials in habitats.
• They are also capable of catabolising many xenobiotic (not naturally occurring) compounds, such as pesticides and other toxic chemicals, and are thus important agents of bioremediation in the environment.
• Special media, such as the O–F medium of Hugh and Leifson must be used for diagnostic tests.
• It utilizes glucose oxidatively with the production of acid only. Lactose and maltose are not utilized.
• Indole, MR, VP and H2S tests are negative.
• It reduces nitrates to nitrites and further to gaseous nitrogen.
• Oxidase-positive or negative.
• Catalase-positive.
• Gelatinase positive.

Genetics

• The mol% G+C content of the DNA is 58–

Importance &/or Pathogenesis

• A number of Pseudomonas is pathogenic.
• Among the fluorescent Pseudomonas, the species Pseudomonas aeruginosa is frequently associated with infections of the urinary and respiratory tracts in humans.
• aeruginosa infections are also common in patients receiving treatment for severe burns or other traumatic skin damage and in people suffering from cystic fibrosis.
• aeruginosa is naturally resistant to many of the widely used antibiotics, so treatment of infections is often difficult.
• The phytopathogenic Pseudomonas generally can be found only on diseased plants.
• Pseudomonas species play important roles in the food industry, where spoilage of meats, poultry and fish occurs, even under refrigerated conditions.

Example

• Pseudomonas aeruginosa

 

Xanthomonas

 

Domain: Bacteria.

Phylum: Proteobacteria.

Class: Gammaproteobacteria.

Order: Xanthomonadales.

Family: Xanthomonadaceae.

Genus: Xanthomonas.

Habitat

• Xanthomonas bacteria grow almost exclusively in plants.

Morphology

• Gram negative straight rods
• Size – 0.4 – 1.0 µm wide by 1.2 – 3.0 µm long
• Motile by a single polar flagellum
• Do not have sheaths or prosthecae
• Non spore former.
• No pili or fimbriae have been reported.
• Most cells have intracellular granules.
• Cells are surrounded by xanthan gum (extracellular polysaccharide, EPS), not recognizable as capsules by light or electron microscopy

Physiology

• Obligately aerobic, having a strictly respiratory type of metabolism with oxygen as the terminal electron acceptor
• Optimum temperature, 25-30 °C
• Temperature range is 4 to 37 °C

Growth & Nutrition

• Growth factors required usually include methionine, glutamic acid, nicotinic acid, or a combination of these.
• No denitrification or nitrate reduction occurs.
• Acid is not produced in purple milk or litmus milk.
• Asparagine is not used as a sole source of carbon and nitrogen.
• Growth is inhibited by 0.1% (and usually by 0.02%) tri phenyltetrazolium chloride
• Catalase positive, Oxidase negative.
• Indole test negative.
• Small amounts of acid are produced from many carbohydrates, but not from rhamnose, inulin, adonitol, dulcitol, sorbitol, meso-inositol or salicin.
• Colonies are usually Mucoid, convex, yellow, smooth and butyrous or viscid.
• Most Xanthomonas strains form yellow, water-insoluble pigments (xanthomonadins) when cultivated on the common growth media.
• Most produce large amounts of extracellular polysaccharide

Genetics

• The mol% G+C content of the DNA is 63-71

Importance &/or Pathogenesis

• Xanthomonasspecies can cause bacterial spots and blights of leaves, stems, and fruits on a wide variety of plant species.
• Xanthomonasspecies produce an extrapolysaccharide called xanthan gumthat has a wide range of industrial uses, including foods, petroleum products, and cosmetics.

Examples

• Xanthomonas alfalfae
• Xanthomonas ampelina
• Xanthomonas campestris
• Xanthomonas citri
• Xanthomona cynarae
  

 

Neisseria

 

Domain:      Bacteria

Phylum:      Proteobacteria

Class II.       Betaproteobacteria

Order IV.     Neisseriales

Family I.      Neisseriaceae

Genus I.       Neisseria

Habitat

• Inhabitants of the mucous membranes of mammals.
• Some species are primary pathogens of humans.

Morphology

• Gram negative, but there is a tendency to resist decolorization.
• Cocci 0.6–1.9 µm in diameter, occurring singly but often in pairs.
• Division of the coccal species is in two planes at right angles to each other, sometimes resulting in tetrads.
• Capsules and fimbriae (pili) may be present.
• Endospores are not present.
• Swimming motility does not occur and flagella are absent.

Physiology

• Some species produce a yellow carotenoid pigment.
• Some species are nutritionally fastidious and haemolytic.
• Optimal temperature, 35–37ºC.
• Optimum pH is 7.0–7.4.
• Exotoxins are not produced.
• Some species are saccharolytic.

Growth & Nutrition

• Neisseria species other than meningitidis and N. gonorrhoeae will grow on plain nutrient agar at 35–37ºc.
• Meningitidis requires mineral salts, lactate, a few amino acids, and glutamic acid as a carbon source.
• Iron is an essential growth factor for gonorrhoeae.
• A high relative humidity (50%) is beneficial to the growth of all species, and CO2 (3–10%) is required for the growth of gonococci and enhances the growth of meningococci on solid media.
• Indole and hydrogen sulfide are not produced and nitrates are not reduced.
• Oxidase...