microbiologist Flashcards

Question

Growth in practical microbiology

Answer 1

microscopic counts: Count the number of cells present Samples dried onto slides or liquid samples -can be stained to increase contrast between cells and their background issues: Without special staining techniques, dead and live cells can’t be distinguished Imprecise Small cells difficult to see under the microscope Motile cells must be killed/immobilised – debris from sample may be mistaken for cells viable counts: Viable cell – able to divide and produce offspring These are usually the cells we’re most interested in AKA a plate count Main assumption – each viable cell will divide to form one colony spectrophotometry: Cells scatter light Turbidity can be used to estimate cell mass in a sample More light scattering = more cell mass = more cells

Answer 2

*Like macroorganisms (animals and plants), microbes have an ecology: A given species lives in certain places but not others Environments differ in their abilities to support diverse microbial populations

Answer 3

*Great metabolic diversity *Primary catalysts of nutrient cycles *Very important members of the ecosystem microenvironment: Microorganisms are very small so only directly experience a tiny local environment *For a typical 3 μm bacterium, a distance of 3 mm is like 2 km for a human *Metabolic activities from nearby microorganisms can alter the conditions *Numerous micro environments can exist within a given habitat diffusion: *If you are small, diffusion often determines the availability of resources *Use microelectrodes to measure oxygen concentration in a soil particle *Many microenvironments within very short distance *Microorganisms near outer edges consume all oxygen before it can diffuse to the centre *Anaerobic organisms thrive near centre *Aerobic organisms live in outer layers

Answer 4

*Pathogenic/symbiotic associations with plants/animals/humans/each other Terrestrial *Soils *Subsurface Aquatic *Freshwater *Coastal/ocean *Deep sea

Answer 5

microbial growth *Most extensive microbial growth takes places on surfaces of soil particles *Highly promoted in the rhizosphere – roots exude nutrients which microbes can absorb water availability: *Water content of soil highly variable *Depends on soil composition, rainfall, drainage and plant cover *Water has minerals dissolved in it = ‘soil solution’ *Water content also affect oxygen levels, waterlogged = low oxygen nutrient availability: *Greatest microbial activity in organic-rich soil surface layers *Especially around rhizosphere *Numbers and activities of microbes greatly depends on type and amount of nutrient present

Answer 6

*Groundwater - Water in soils and rocks deep underground *A little explored microbial habitat *Microbial life extends down at least 3 Km into the Earth *May account for as much as 40% of global biomass deep level microbes: *Chemolithotrophic and autotrophic bacteria, and archaea found at 3 Km deep in South Africa *Must survive on a very nutrient poor diet *Probably use H2 as the electron donor for respiration highly variable conditions: *Cell numbers in groundwater vary by several orders of magnitude (10^2 -10^8 per ml) *Due to nutrient availability – especially dissolved organic carbon *Generation times vary from days to centuries

Answer 7

Freshwater vs marine differ in many ways: *Salinity *Average temperature *Depth *Nutrient content freshwater: *Highly variable in resources and conditions *Both oxygen consuming and oxygen producing organisms present *The balance controls the cycle of nutrients oxygenic phototrophs: Include algae and cyanobacteria *Primary producers-Energy comes from light *Planktonic-Floating *Benthic-Attached to bottom or sides of lake/stream habitats changes with depth

Answer 8

Very low nutrient levels, especially nitrogen, phosphorus and iron *Water temperatures are cooler & are more constant with seasons than freshwater *Overall microbial numbers are lower in marine compared to freshwater habitats (106 /ml vs 107 /ml) microbes in the ocean: *Very small cells *Typical characteristic of living in nutrient-poor environment *Requires less energy for cell maintenance *Require greater number of transport enzymes relative to cell volume to acquire nutrients from very dilute environment *Oxygenic photosynthesis in the oceans is a major factor in controlling the Earth’s carbon balance *so important because the oceans are so large! growth with depth: *Bacteria predominate in waters above 1000 m *Photic zone = where light can penetrate to *Oceans contain the largest microbial biomass on the surface of the Earth hydrothermal vents: *Underwater hot volcanic springs *Found 1000 m to greater than 4000 m deep

Answer 9

Organisms must be finely tuned to their conditions 1.Nutrient availability 2.Temperature 3.pH 4.Moisture 5.Oxygen 6.Pressure 7.Light Extremophile- An organism whose growth is dependent on extremes of temperature, salinity, pH, pressure, or radiation, which are generally inhospitable to most forms of life

Answer 10

*Arguably the most important factor affecting growth *All species have: Minimum temperature – growth isn’t possible below Optimum temperature – growth is most rapid Maximum temperature – growth isn’t possible above *these are cardinal temps. which are different for every species

Answer 11

psychrophile *Optimal growth temperature 15°C or lower *Max growth temperature 20°C *Killed by warming, found in constantly cold environments *Psychromonas – sea ice bacterium – grows at -12°C – lowest known *But probably can go lower *Some enzymes found to function at -20°C

Answer 12

*Enzymes have optimal activities at low temperatures *Molecular basis not fully understood Primary structure: More polar amino acids Fewer weak bonds Secondary structure: Greater α–helix, less β–pleated sheet Gives protein greater flexibility (β–pleated sheets are quite rigid) *Cytoplasmic membranes must remain functional High content of unsaturated and shorter-chain fatty acids Helps membrane remain in semifluid state at low temperatures “Cold-shock” proteins: *Maintain other proteins’ activity and bind specific mRNAs to facilitate their translation *Not limited to psychrophiles – e.g. found in E. coli Cryoprotectants: *Solutes (e.g. glycerol or sugars) that help prevent the formation of ice-crystals in the cell

Answer 13

thermophile *Growth temperature optimum greater than 45°C *Less extreme than the hyperthermophiles *Found in a wide range of habitats: *Edges of hot springs *Soil surfaces *Fermenting environments *Artificial environments e.g. hot water heaters hyperthermophiles: Growth temperature optimum greater than 80°C Found in hot springs Only prokaryotes Growth rates often quite high – generation times as short as 1hr have been recorded The most heat-tolerant example known is Methanopyrus – can grow at 122°C

Answer 14

Heat-stable enzymes and proteins Increased DNA stability Heat-stable membranes hyperthermophile membranes Do not contain fatty acids Have C40 hydrocarbons (repeating units of isoprene) bonded to glycerol phosphate by ether (rather than ester) link Forms a monolayer

Answer 15

Grow best at pH 5.5 or below Different classes optimised to different pHs Those with a pH optima of below 1 are very rare Most cannot grow at pH 7

Answer 16

Grow best at pH 8 or above A few extremophiles have a very high pH optima – as high as pH 11 Found in environments such as soda lakes and high-carbonate soils

Answer 17

MUST REMAIN NEAR NEUTRALITY Optimal pH for growth refers to extracellular environment only Intracellular pH must stay near pH 7 to prevent destruction of macromolecules

Answer 18

Halophiles - Require NaCl for growth Halotolerant – can tolerate NaCl, but grow best in absence of solute