Group 4 Rhizobium, Enterobacteria, and Actinomycetes

1
Group 4 Rhizobium, Enterobacteria, and
Actinomycetes

• By Matt Vermillion, Jennifer LaShell, and Gavin
  Tate

2
What is Rhizobium?

• Rhizobia comes from the Greek words Riza, which
  means root and Bios, which means life.
• Rhizobia are soil bacteria that acts a primary
  symbiotic fixer of nitrogen. The bacteria mainly
  infect the roots of plants, which leads to the
  formation of lumps or nodules where the Nitrogen
  fixation takes place.
• Although much of the nitrogen is removed when
  protein-rich grain or hay is harvested, some
  Nitrogen still remains in the soil for future
  crops.
• This is very important when nitrogen fertilizer
  is not used, as in organic rotation schemes or
  some less-industrialized countries.
• The bacteria mainly infect the roots of plants,
  which leads to the formation of lumps or nodules
  where the Nitrogen fixation takes place.

3
Rhizobium Chemical composition, shape,
nutrition and movement.

• Rhizobium are composed of a number of
  polysaccharides and deal with Nitrogen-Fixing.
• Rhizobium are regular in structure meaning they
  appear as straight rods, but when rhizobia are in
  root nodules the nitrogen fixing form exists as
  irregular cells that are often club or Y-shaped.
• Rhizobium that are in the soil are free living
  and motile, feeding on the remains of dead
  organisms.

4
Root Nodule Formation
5

• The legume-rhizobium symbiosis is a classic
  example of mutualism. Several unrelated strains
  infect each individual plant, any one strain
  could redirect resources from nitrogen fixation
  to its own reproduction without killing the host
  plant upon which they all depend. But this form
  of cheating should be equally tempting for all
  strains, a classic tragedy of the commons. It
  turns out that legume plants guide the evolution
  of rhizobia towards greater mutualism by reducing
  the oxygen supply to nodules that fix less
  nitrogen, thereby reducing the frequency of
  cheaters in the next generation.

6
Rhizobium Unique Characteristics

• There are several different genera of rhizobia.
  All of them belong to the Rhizobiales, a close
  monophyletic group of proteobacteria.
• The plant pathogen Agrobacterium is a closer
  relative of Rhizobium than the rhizobia that
  nodulate soybean (and may not really be a
  separate genus). The genes responsible for the
  symbiosis with plants, however, may be closer
  than the organisms themselves, acquired by
  horizontal transfer rather than from a common
  ancestor.

7
Rhizobium - Importance

• Nitrogen fixation is the second most important
  biological process on earth.
• Importance in agriculture
• Legumes such as peas, beans, lentils, soybeans,
  alfalfa, and clover help to feed the
  meat-producing animals which feed humans.
• Crop yields are greatly improved in nodulated
  plants legumes can grow well in poor soil where
  there is not enough fixed nitrogen to support
  other types of plants.
• After harvest legume roots left in the soil decay
  easily releasing organic nitrogen compounds for
  uptake by the next generation. Farmers take
  advantage of this natural fertilization by
  rotating a leguminious crop with a non
  leguminious one. This helps the crop grow
  easier.

8
Rhizobium - Importance

• Although much of the nitrogen is removed when
  protein-rich grain or hay is harvested,
  significant amounts can remain in the soil for
  future crops. This is especially important when
  nitrogen fertilizer is not used, as in organic
  rotation schemes or some less-industrialized
  countries. Nitrogen is the most commonly
  deficient nutrient in many soils around the world
  and it is the most commonly supplied plant
  nutrient. Supply of nitrogen through fertilizers
  has severe environmental concerns. Nitrogen
  fixation by Rhizobium is also beneficial to the
  environment.

9
Enterobacteria What is it?

• Members of the family Enterobacteriaceae which
  include familiar pathogens such as Salmonella and
  Escherichia coli.

• Genetic studies place them among the
  Proteobacteria and give them their own order
  Enterobacteriales.

10
Scientific Classification of Enterobacteria

• Family Enterobacteriaceae
• Order Enterobacteriales

• Kingdom Bacteria
• Phylum Proteobacteria
• Class Gamma Proteobacteria

11
Morphology of the Enterobacteria

• Rod Shaped
• Typically 1-5 µm (micrometers) long
• Gram Negative stains

Salmonella is a Gram negative Enterobacteria
12
Mode of MovementEnterobacteria

• Most have flagella, but some are non-motile.
• Possess Pili

Flagella
13
EnterobacteriaChemical Composition

• Enterobacteria usually lack Cytochrome C Oxidase.
• Contains a Capsule Capsule is a polysaccharide
  layer surrounding the surface of some bacterial
  cells and is a major factor that functions as a
  protective barrier .
• Antigenic structure
• K (capsular) antigens capsular polysaccharide
• H (flagellar) antigens flagellar proteins of
  motile genera and species absent in non-motile
  genera
• O (somatic) antigens O-specific polysaccharide
  side chain of lipopolysaccharide

14
Unique Facts-Enterobacteria

• Most species grow well at 37 and some grow
  better at 25 -30
• All species attack glucose, forming acid.
• All are aerobic but can be facultative anaerobic
• Over 30 genera and 120 species

15
(No Transcript)
16
Enterobacteria Medical and Pathogenic Importance

• Salmonella
• E. Coli
• Pneumonia
• Meningitis
• Most members of the Enterobacteriaceae Family
  cause secondary infections of wounds, the urinary
  and respiratory tracts, and the circulatory
  system

17
Actinomycetes-Unique Characteristics

• Anaerobic
• Almost always produce granules
• Can affect cattle, causing the disease Lumpy
  Jaw
• Produce Spores
• Needs organic C for energy

18
Medical Importanceof Actinomycetes

• Most common cause is Actinomyces israelii which
  infects both man and animals
• Commonly found in the jaw, but can also be found
  in the abdominal area
• Can produce antibiotics
• Gram-positive bacteria

19
Morphology-Actinomycetes

• Rod shape
• Frequently branches (hyphae) ranging from .5-1.5
  micrometers in length
• Genetic material is coiled up in the hyphae

20
Actinomycotic mycetomatous granule due to the
bacteria Streptomyces somaliensis. Streptomyces
are Gram-positive aerobic actinomycetes known for
their production of antimicrobial substances.
Though they seldom cause human disease,
infections can cause lesions of the skin.
21
Composition of Actinomycetes

• They form mycelia of thin branching hyphae.
• DNA is coiled inside the hyphae.
• The cell wall of the hyphae is made up of
  cross-linked polymer containing short chains of
  amino acids and long chains of amino sugars
• No membrane-bound cell organelles

22

• http//www.life.umd.edu/classroom/bsci424/pathogen
  descriptions/Enterobacteriaceae.htm
• http//www.microbiologyonline.org.uk/forms/rhizobi
  um.pdf
• http//pathmicro.med.sc.edu/mycology/mycology-2.ht
  m