BIOREMEDIATION : QUESTIONS AND ANSWERS

                                                         

QUESTION ONE

When hydrogen peroxide is used as a source of oxygen, it discriminates in favor of peroxide-tolerant bacteria and against some efficient co metabolizers like methanotrophs. Why?

Methanotrophs are bacteria that are able to metabolize methane as their only source of carbon and energy. They can grow aerobically or anaerobically and require single-carbon compounds to survive.However, hydrogen peroxide used as a source of oxygen increases the oxygen and assist in cleaning greatly. It releases too much oxygen too quickly for aerobic microorganism for biodegradation that is in situ.

When hydrogen peroxide is used as a source of oxygen, peroxide-tolerant bacteria are favoured, these are aerobic bacteria that use oxygen to become active, hence able to degrade the contaminants. Cometabolizers like methanotrophs do not use oxygen but require methane for degradation, so when hydrogen peroxide is used as a source of oxygen it affects methanotrophs degradation.

QUESTION TWO

Explain in details what is meant by

i.                    Direct metabolism

ii.                  Aerobic co metabolism under aerobic mechanism of degradation of some chlorinated compounds.

Direct metabolism;

Microorganisms use a wide range of metabolic pathways to harvest energy from their environment. In some cases, pollutants serve as the carbon and energy source for microbial growth, while in other cases; pollutants serve as the terminal electron acceptor. This manifests itself in the diverse ability of microbes to transform and degrade toxic molecules.

Direct metabolism is a mechanism of biodegradation in which chlorinated compounds are metabolized directly by microorganisms. They oxidize the carbon and excrete the chlorine as inorganic chloride. This is fairly uncommon, because there is little or no energy to be gained by oxidizing a carbon-chlorine bond.

Moreover direct metabolism also described as anaerobic reductive dechlorination is a biodegradation reaction in which bacteria gain energy and grow as one or more chlorine atoms on a chlorinated hydrocarbon are replaced with hydrogen. In that reaction the chlorinated compound serves as the electron acceptor and hydrogen serve as the direct electron donor.   Hydrogen used in the reaction typically is supplied indirectly through the fermentation of organic substrates.

i.                    Aerobic co metabolism under aerobic mechanism of degradation of some chlorinated compounds

A microorganism that lives on a nonchlorinated organic compound produces an enzyme that happens to break down the chlorinated compound. The microbe gains nothing by the dechlorination; the process works because the microbe is inefficient: Aerobic Co metabolism is a biodegradation reaction in which chlorinated hydrocarbon is fortuitously degraded by an enzyme or cofactor produced during microbial metabolism of another compound. In such case, biodegradation of the chlorinated compound does not appear to yield any energy or growth benefit for the microorganism mediating the reaction.

Under Aerobic conditions several different types of bacteira including methane oxidizing bacteria, ammonia oxidizing bacteria and some phenol utilizing bacteria can cometabolized  or cooxydized trichloethene, dichloethene, and vinyl chlroride. In general cometabolism of chlorinated ethenes is mediated by monoxygenase enzymes with relaxed specificity that oxidized a primary substrate and cooxidized the chlorinated compound. In the presence of methane for example, methanotrophs produce methane monoxygenase which oxydized methane for methanol and  can also cooxydized trichloroethene. For Aerobic cometabolism three key factors must be present; a primary substratek, oxygen, bacteria capable of producing nonspecific monoxygenase. These are biological processses responsible for biodegradation of some chlorinated compounds mentioned above.