Transcript Soil Bacteria Autochthonous (k-selective, k

Soil Bacteria
Microorganisms:
• Soil - a favorable habitat for
microorganisms
• inhabited by a wide range of
microorganisms, including bacteria,
fungi, algae, viruses and protozoa.
• Microorganisms are found in large
numbers
in soil - usually between one and ten
million
microorganisms are present per gram of
soil.
Microorganisms and their significance:
• Can increase the amount of nutrients present in the soil.
• The microorganisms, which improve the fertility
status of the soil and contribute to plant growth,
have been termed ‘biofertilizers’.
Microorganisms and their significance:
• Antagonistic to
the pathogens and can prevent the
infection of crop plants. Competition for nutrients
and/or production of inhibitory compounds such as
secondary metabolites (antimicrobial metabolites and
antibiotics) and extracellular enzymes.
Microorganisms and their significance:
• Other
soil microorganisms produce compounds that
stimulate the natural defense mechanisms of the plant
and improve its resistance to pathogens.
• Biological control.
significance:
• Responsible for the decomposition of the
organic matter entering the soil and therefore in
the recycling of nutrients in soil.
• Certain soil microorganisms such as mycorrhizal
fungi can also increase the availability of mineral
nutrients (e.g.phosphorus) to plants.
Major groups of soil microorganisms
Bacteria:
• Numerically abundant (109 cells/g soil)
but most non-culturable
• Along with fungi, most important
decomposers of organic matter
• Bacteria and fungi being the most prevalent.
• However, the availability of nutrients is
often limiting for microbial growth in soil
and most soil microorganisms may not be
physiologically active in the soil at a given
time.
Bacteria:
• Specialized groups participate in all biogeochemical
cycles
• Their extracellular polymers help bind soil particles
into aggregates
• Some form beneficial or pathogenic interactions
with plants
Soil bacteria
Autotrophic
Decomposers
Mutualism
Pathogens
Chemolithotrophs
1. Nitrogen fixation
2. NH3 assimilation
3. Ammonification
4. Nitrosification
5. Nitrification
6. Nitrate assimilation
7. Dissimilatory nitrate reduction
8. Denitrification
1. Nitrogen fixation N2 → NH3 (aerobic)
• free-living: Azotobacter, cyanobacteria;
• symbiotic: Rhizobium
• (anaerobic): Clostridium perfringens, purple &
green sulfur phototrophs.
2. NH3 assimilation (aerobic & anaerobic)
3. Ammonification (organic N→ NH3)
4. Nitrosification (aerobic), Nitrosomonas
5. Nitrification (aerobic), Nitrobacter
6. Nitrate assimilation (NO3-→ NH3 → amino acids)
7. Dissimilatory nitrate reduction (NO3-→ NO2-)
8. Denitrification (NO3- → N2) Bacillus, Pseudomonas,
Growth in the environment
Sergei Winogradasky 1853
Autochthonous (k-selective, k-strategy): metabolize slowly in soil,
utilizing slowly released soil organic matter as a substrate.
Oligotroph
Zygochthonous (r-selective, r-strategy): rapid growth , depending
on substrate avalability, dormant ,Copiotrophs
Allochthonous: are introduced into soil and survive for only short
time.
Arthrobacter 40%
Bacillus
70%
Psudomonas 15%
Agrobacterim 5%
‫‪Nutrition of Bacteria in soil‬‬
‫احتیاجی به فاکتورهای رشد ندارند ‪%10‬‬
‫یک یا چند اسیدآمینه و یا ویتامین نیاز دارند ‪%10+%10‬‬
‫هم اسیدامینه و هم ویتامین الزم دارند‬
‫به مخلوطی از فاکتورهای پیچیده نیاز دارند ‪%30‬‬
‫‪Complex mixture of growth factors‬‬
Environmental influences
Moisture, aeration, temperature, Organic matter, pH, Season,
Depth
1) Enrichment and isolation methods
2) Serial dilution plate techniques (MPN) most
probable number. (CFU) colony forming unit. Viability
In Situ Soil Microscopy
Rossi buried slide technique
Capillary
Staining
Fluorescent Staining
Viability Staining
dyes (acridine orange )
(Propidium iodine)
Genetic Staining : Fluorescent in situ hybridization (FISH)
Nitrifying
Nitrite-oxidizing
Pathogens bacteria in the soil
Bacillus antheracis , Clostridium tetani, Clostridium botulinum
Salmonella , Coxiella , Streptococcus
Agrobacterium , Pseudomonas, Erwinia (plant pathogens)
Killing, Lysing and feeding of bacteria
1- Myxobacteria
Gram negative, rods(rounded or tapered ends),
aerobic, fruiting bodies. Myxococcus, Chondroccus
2- Bdellovibrio (feeding, Lysing & Killing)
3- Protozoa