Oligotrophic microbes are able to survive in extremely nutrient-poor environments through various adaptations. They have low metabolic and growth rates compared to copiotrophs found in nutrient-rich environments. Examples of oligotrophic environments include deep ocean sediments, glacial ice, nutrient-deficient soils, and large areas of the open ocean. Specific oligotrophic bacteria that have adapted to these conditions include Pelagibacter ubique, the most abundant bacteria in oceans, and soil-dwelling Collimonas species, which can obtain nutrients from fungi and mineral weathering.

1. OLIGOTROPHIC MICROBES – LIFE AT
LOW NUTRIENT CONCENTRATIONS
SYED MUHAMMAD KHAN
(BS HONS. ZOOLOGY)

2. INTRODUCTION
 Low nutrient concentration in the environment serves as a limiting factor for microbial
growth.
 Most of the microbes, present in the environment are heterotrophs and hence they
depend on the available nutrients. Cells mainly use nutrients for two purposes:
1. Maintenance of cellular functions
2. Growth (in both size and number)
 Heterotrophic microbes may be either:
1. Oligotrophs – organism that can live in environments with very low levels of nutrients.
2. Copiotrophs – organisms found in environments rich in nutrients, particularly carbon.

3. COMPARISON BETWEEN OLIGOTROPHS
AND COPIOTROPHS
OLIGOTROPHS
 They have low growth and metabolic
rates.
 They are highly efficient in substrate
scavenging.
 They frequently live attached to surfaces.
 They form polymers and storage products
even while starving, and often aggregate.
 Many oligotrophs alter their morphology
(surface to volume ratio) with changing
nutrient concentrations.
COPIOTROPHS
 They have a low substrate affinity.
 They have high growth and metabolic
rates.

4. COMPARISON BETWEEN OLIGOTROPHS
AND COPIOTROPHS
Graphs comparing the growth patterns of oligotrophs and copiotrophs.

5. LIMITATIONS OF CONVENTIONAL
CULTURING METHODS
 Culturing a sample of microbes from its natural context (soil, water, etc.)
to a nutrient medium will not allow one to observe all of the species,
because:
1. Oligotrophs will be unable to grow in such a nutrient rich medium.
2. Only copiotrophs can be detected via this method.

6. GENERAL RESPONSE OF MICROBES TO
STARVATION
 The life cycle of some specialized prokaryotes, fungi, and protozoa includes a
resistant, quiescent stage, variously termed endospore, myxospore, cyst,
conidium, etc.
 Such developmental stages in microbial life cycles are triggered by environmental
cues, especially starvation, received by the microorganism.
 The resulting resting stages typically surround vital cytoplasmic constituents with
a thick-walled structure that confers resistance to:
1. Starvation
2. Extreme environmental conditions ranging from heat, to desiccation, to acidity,
to γ-irradiation, to salinity, to UV light.

7. GENERAL RESPONSE OF MICROBES TO
STARVATION
CELLULAR RESPONSE
 Commonly a sensor protein is embedded within, but extending out from,
the cytoplasmic membrane of the cell.
 The environmental change causes an allosteric (structural) alteration in
protein conformation which leads to its self-catalyzed binding to a
phosphate molecule.The term “sensor kinase” applies.
 The phosphorylation triggers a subsequent series of phosphorylation
events that influence the activity of one or more regulatory proteins.

8. GENERAL RESPONSE OF MICROBESTO
STARVATION
 These, in turn, control gene transcription by binding
to the promoter or attenuator regions of one or
more operons.
 Following translation of the transcribed genes,
protein-catalyzed metabolic changes in the cell
eventually deliver negative feedback to the
regulatory circuit.
 Overall, the cell’s response is matched to the
severity of the nutritional stress.
 When the stress is relieved, the cytoplasmic sensor
resumes its previous non-phosphorylated state.
Cellular Response to Starvation

9. HOW DO MICROBES BECOME FIT FOR
SURVIVAL
 The following five processes render microbial populations “fit” for starvation
survival:
1. All metabolic processes are reduced to a dormant or near-dormant state.
2. When starved, many species will increase in cell number via reductive division,
resulting in reduced cell size – hence forming ultramicrobacteria.
Ultramicrobacteria are bacteria that are smaller than 0.1 μm3 under all growth
conditions. They possess a relatively high surface-area-to-volume ratio due to
their small size, which aids in growth under oligotrophic (i.e. nutrient-poor)
conditions.
3. In the starvation/survival process, any cellular energy reserve material is used to
prepare the cell for survival.

10. HOW DO MICROBES BECOME FIT FOR
SURVIVAL
4. All metabolic mechanisms are directed to the formation of specific proteins,
ATP, and RNA so that the cell, when it encounters a substrate is equipped to use
it immediately without a delay that otherwise would occur if initial amounts of
energy had to be expended for the synthesis of RNA and protein. Both RNA and
protein synthesis are high energy-consuming processes, and the high ATP level
per viable cell is thus available and used primarily for active transport of
substrates across the membrane. Protective starvation proteins are also
synthesized and substrate capturing is enhanced (i.e. amino acid uptake).
5. The change to a smaller cell size on starvation (miniaturization) permits greater
efficiency in scavenging what little energy-yielding substrates there are in the
environment and also enhances survival prospects against other adverse
environmental factors.

11. NUTRIENT DEFICIENT ENVIRONMENTS
 The word oligotrophic may also be used as an adjective to refer to environments
that offer little to sustain life, organisms that survive in such environments, or the
adaptations that support survival.
 The word “oligotroph” is a combination of the Greek adjective “oligos” meaning
“few” and the adjective “trophikos” meaning “feeding”.
 Oligotrophic environments include:
• Deep oceanic sediments
• Caves
• Glacial and polar ice
• Deep subsurface soil
• Aquifers
• Ocean waters
• Leached soils

12. OLIGOTROPHIC SOILS
 The oligotrophic soil environments include agricultural soil, frozen soil, etc.
 Various factors, such as decomposition, soil structure, fertilization and temperature, can
affect the nutrient-availability in the soil environments.
DEEP SUBSURFACE SOILS
 Generally, the nutrient becomes less available along the depth of the soil environment.
 On the surface, the organic compounds decomposed from the plant and animal debris are
consumed quickly by other microbes, resulting in the lack of nutrient in the deeper level of
soil.
 The metabolic waste produced by the microorganisms on the surface also causes the
accumulation of toxic chemicals in the deeper area.
 It is difficult for water and oxygen to diffuse to lower depths.
 The presence of mineral under the soil provides the alternative sources for the species
living in the oligotrophic soil.

13. OLIGOTROPHIC SOILS
FROZEN SOILS
 In terms of polar areas, such as Antarctic and Arctic region, the soil
environment is considered as oligotrophic because the soil is frozen with low
biological activities.
 The most abundant species in the frozen soil are those of Actinobacteria,
Proteobacteria, Acidobacteria and Cyanobacteria, together with a small
amount of archaea and fungi.
 Actinobacteria can maintain the activity of their metabolic enzymes and
continue their biochemical reactions under a wide range of low temperature.
 In addition, the DNA repairing machinery in Actinobacteria protects them
from lethal DNA mutation at low temperature.

14. OLIGOTROPHIC LAKES
 An oligotrophic lake is a lake with low primary productivity, as a result of low nutrient
content.
 These lakes have low algal production, and consequently, often have very clear
waters, with high drinking-water quality.
 The bottom waters of such lakes typically have ample oxygen; thus, such lakes often
support many fish species such as lake trout, which require cold, well-oxygenated
waters.
 The term oligotrophic is used to distinguish unproductive lakes, characterized by
nutrient deficiency, from productive, eutrophic lakes, with an ample or excessive
nutrient supply.
 Oligotrophic lakes are most common in cold regions underlain by resistant igneous
rocks (especially granitic bedrock).

16. OLIGOTROPHIC LAKES
LAKEVOSTOK
 It is a freshwater lake which has been isolated from the world beneath 4 km of
Antarctic ice and is frequently held to be a primary example of an oligotrophic
environment.
 The average water temperature of Lake Vostok is calculated to be around −3 °C
(27 °F).
 It remains liquid below the normal freezing point because of high pressure from
the weight of the ice above it.
 Geothermal heat from the Earth's interior may warm the bottom of the lake,
while the ice sheet itself insulates the lake from cold temperatures on the surface.

17. OLIGOTROPHIC LAKES
 Lake Vostok is an oligotrophic extreme environment, one that is expected to be
supersaturated with nitrogen and oxygen, around 50 times more than ordinary
freshwater lakes on Earth's surface.
 The sheer weight and pressure of the continental ice cap on top of Lake Vostok is
estimated to contribute to the high gas concentration.
 Analysis of ice samples showed ecologically separated microenvironments.
 Isolation of microorganisms from each microenvironment led to the discovery of a
wide range of different microorganisms present within the ice sheet.
 Traces of fungi have also been observed which suggests potential for unique
symbiotic interactions.
 The lake’s extensive oligotrophy has led some to believe parts of lake are completely
sterile.

18. A map of LakeVostok - Antarctica Layers of the Lake

19. OLIGOTROPHIC LAKES
KROK (CROOKED) LAKE
 Krok Lake is an irregular-shaped glacial lake about 7 km long in Antarctica.
 The lake was partially mapped by Norwegian cartographers from air photos taken
by the Lars Christensen Expedition (1936–37) and named “Krokvatnet” (the
crooked lake).
 It is an ultra-oligotrophic glacial lake with a thin distribution of heterotrophic and
autotrophic microorganisms.
 The microbial loop plays a big role in cycling nutrients and energy within this lake,
despite particularly low bacterial abundance and productivity in these
environments.
 The little ecological diversity can be attributed to the lake's low annual
temperatures.

20. OLIGOTROPHIC OCEANS
 In the ocean, the subtropical regions north and south of the equator are regions in which
the nutrients required for phytoplankton growth (for instance, nitrate, phosphate and
silicic acid) are strongly depleted all year round.
 These areas are described as oligotrophic and exhibit low surface chlorophyll.
 They are occasionally described as "ocean deserts".
NORTH PACIFIC SUBTROPICAL GYRE
 The North Pacific Subtropical Gyre (NPSG) is the largest contiguous ecosystem on Earth.
 Low nutrient concentrations and thus a low density of living organisms characterize the
surface waters of the NPSG.
 The low biomass results in clear water, allowing photosynthesis to occur to a substantial
depth.

21. OLIGOTROPHIC OCEANS
 The NPSG is classically described as a two-layered system:
1. The upper, nutrient-limited layer accounts for most of the primary
production, supported primarily by recycled nutrients.
2. The lower layer has nutrients more readily available, but
photosynthesis is light-limited.

22. DEEP OCEAN SEDIMENTS
 The deep benthic habitats of the ocean consist of some of the most food-poor
regions on the planet.
 One of the sources of nutrients to this deep ocean habitat is marine snow.
 Marine consists of detritus (dead organic matter) which falls from the surface
waters where productivity is highest.

23. EXAMPLES OF OLIGOTROPHIC BACTERIA
Pelagibacter ubique
 It is the most abundant organism in the oceans and quite
possibly the most abundant bacteria in the entire world.
 They have sensors for nitrogen, phosphate, and iron
limitation, and a very unusual requirement for reduced
sulfur compounds.
 They have been molded by evolution in a low nutrient
ecosystem.
 A population of P. ubique cells can double every 29 hours,
which is fairly slow, but they can replicate under low
nutrient conditions.
 P. ubique can be grown on a defined, artificial medium
with additions of reduced sulfur, glycine, pyruvate and
vitamins. Pelagibacter ubique (SEM)

24. EXAMPLES OF OLIGOTROPHIC BACTERIA
Collimonas spp.
 It is one of the oligotrophic microbes
capable of living in the nutrient deficient
soils.
 One common feature of the environments
where Collimonas live is the presence of
fungi.
 Collimonas have the ability of not only
hydrolyzing the chitin produced by fungi for
nutrients, but also producing materials to
protect themselves from fungal infection.
 Additionally, Collimonas can also obtain
electron sources from rocks and minerals by
weathering.
Collimonas spp.

25. THE END