A local pesticide-producing plant has been leaking high concentrations of 2,4-di
ID: 147603 • Letter: A
Question
A local pesticide-producing plant has been leaking high concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) into a cellulose-rich soil for years. In an attempt to reduce the 2,4-D concentrations in the soil, scientists found that 2,4-D degrading microorganisms were already present in the soil.
(a) Explain how the presence of 2,4-D degrading microorganisms was determined. Individual steps do not need to be provided but explain the method/approach and why this would provide the needed information.
(b) Taking into consideration the nutrients required for microbial growth in general, provide two reasons why the cell yield on 2,4-D might be low?
(c) Of the metabolisms we discussed (aerobic/anaerobic respiration, fermentation, aerobic/anaerobic chemolithotrophy, oxygenic/anoxygenic photosynthesis), predict the dominant metabolism and explain why you expect this metabolism to be most abundant.
(d) Could other metabolisms be present? If yes, explain what other metabolisms are present and why they are present. If no, explain why other metabolisms are not present.
Explanation / Answer
a) 2,4-D degrading microbes can be identified based on the
Collection of soil samples from different places.
Soil sample homogenisation and mixing thoroughly.
Assay for herbicide tolerance can be performed. It involves serial dilution in 0.9% NaCl to determine optimal dilution.
Plating onto selective as well as rich medium nutrient agar and nutrient agar with and without 2,4-D(concentration specified for fields).
Incubation of the plates. Selection of 2,4 D- resistant/ tolerant strains.
These strains are selected and stored (cryopreserved for future use).
These bacteria can be used to measure the amount of 2,4- D in the culture by HPLC.
The bacterial cells can be grown and from the supernantent the 2,4- D can be separated by HPLC . 2,4- D needs to be separated using a C18 column followed by elution. It can be detected at a specified wavelength.
The process of 2,4- D degradation can be monitored by observing the peak of 2,4- D. The peak of 2,4- D should decrease with increasing the incubation time. It can be compared with the control having no bacteria. Control sample should give nearly 100% peak compared to the test samples containing bacteria.
The 2,4- D degrading bacterial enzymes can be identified and further characterisation can be used by performing different biochemical assays and bioinformatic analysis.
By comparing their genome sequences with the available genome sequences in the database to assign functionally characterise them.
b) Cell yield on 2,4- D might be low because of the reason
Some bacterial strains will be able to degrade and utilise 2,4- D efficiently thus their growth will be fast whereas those which cannot utilise/degrade it so efficiently will have slowgrowth, having a longer lag phase leading to low cellular yield.
c) The metabolism of those bacteria can be aerobic and anerobic both and fermentive AND Oligotrophic metabolism os required to open the chain.
d) Other metabolisms might be present. Since the bacteria might be varying from symbiotic to non-symbiotic. Thus there might be some possibility that different metabolic pathways might be involved together in degradation process.
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