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#environmental factors

17 public questions tagged with this topic.

Dictyostelium

Ammonia favors differentiation into:

Ammonia, catabolic byproduct accumulating within slug interior, influences cell fate and timing of culmination. Elevated ammonia increases intracellular cAMP via inhibition of RegA phosphodiesterase, activates PKA, and promotes prespore gene expression while suppressing prestalk vacuolization. Tip region, where ammonia volatilizes, maintains lower concentration permitting prestalk differentiation. In vitro monolayer assays demonstrate ammonium chloride addition favors prespore markers and inhibits ecmB induction. Low ammonia would favor prestalk. Ammonia does not directly drive migration or division but acts as diffusible inhibitor linking nitrogen metabolism to developmental decision, ensuring prespore bias in regions of high metabolic activity.

Ref: Cell Reports, Ammonia regulation of Dictyostelium cell fate - prespore promotion and prestalk repression.

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Dictyostelium

High osmolarity inhibits spore germination via:

High osmolarity within sorus fluid maintains spore dormancy preventing precocious germination while spores remain in fruiting body. Sensor adenylyl cyclase G, ACG, contains extracellular CHASE domain coupled to cyclase domain, activated by elevated osmolytes raising intracellular cAMP and sustaining PKA-mediated inhibition of germination genes. Upon dispersal into hypotonic environment such as soil water film, ACG activity drops, cAMP falls, and discoidin and germination proteins become expressed. ACA mediates aggregation; ACB mediates culmination; RegA is intracellular phosphodiesterase antagonizing germination pathway downstream of ACG rather than osmosensor itself, making ACG central to environmental sensing.

Ref: Current Biology, ACG osmosensor adenylyl cyclase - high osmolarity inhibition of spore germination via PKA.

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Bioremediation

Which factor does NOT affect bioremediation?

Bioremediation success reflects interplay between microbial physiology and environmental physicochemistry governing enzymatic function, bioavailability and cell growth. Temperature directly influences membrane fluidity, protein folding and reaction rates according to Arrhenius relationship; mesophilic degraders exhibit optimum around 20 to 30 Celsius while psychrophiles slower and thermophiles require elevated energy for dioxygenase stability. pH around 6.5 to 8.0 maintains proton motive force across membrane, optimal ionization of catalytic residues histidine and aspartate in monooxygenase active centers and solubility of nutrients. Oxygen availability determines redox potential between plus 300 mV aerobic and minus 300 mV anaerobic, dictating whether oxygenase-mediated pathways requiring molecular oxygen as cosubstrate for alkB or anaerobic respiratory routes using nitrate, Fe(III) or sulfate dominate. Nutrient supply maintaining C:N:P near 100:10:1, contaminant concentration below toxic threshold, soil texture affecting aeration and moisture holding capacity also influence. Magnetic field strength exerts negligible direct effect on central metabolism, gene expression or electron transport except for magnetotactic bacteria aligning via magnetosomes; no mechanistic link connects geomagnetic flux to catabolic rates, so field strength excluded among determining factors.

Ref: EPA Factors affecting bioremediation 2000; Singh et al. Journal Environmental Biology 2008 environmental parameters; Campbell Ecology.

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Microbial Physiology

Which environmental factor does NOT directly affect bacterial growth?

Bacterial growth responds strongly to physicochemical factors directly influencing enzyme catalysis, membrane fluidity and solute transport. Temperature governs rate constants via Arrhenius and protein denaturation, pH alters active site ionization and magnitude of proton motive force used for ATP synthesis, water activity and osmotic pressure control turgor needed for elongation, oxygen concentration determines whether aerobic respiration with oxygen as electron acceptor, anaerobic respiration with nitrate, or fermentation dominates energy metabolism. Light intensity unlike in phototrophic cyanobacteria and purple photosynthetic bacteria that possess specialized photosystems with chlorophyll a and bacteriochlorophyll converting photon energy to ATP and NADPH has negligible direct effect on chemotrophic heterotrophs such as Escherichia coli, Staphylococcus aureus or Bacillus subtilis that obtain energy solely via oxidation of organic compounds and chemiosmosis. Although ultraviolet light can generate thymine dimers causing indirect DNA damage, visible light intensity is not considered growth-limiting factor equivalent to nutrients, temperature or pH in standard predictive models like Gamma hypothesis used for food safety risk assessment and fermentation optimization for typical non-phototrophic bacteria.

Ref: Prescott's Microbiology, 11th ed., Chapter 7: Environmental Factors Affecting Growth and Light Intensity.

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