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The below mentioned article provides a note about the types of hydrocarbons used as substrates for growth by various microorganisms.
Yes, some type of hydrocarbons can serve as growth substrates. This type of organisms is ecologically important, e.g. in the degradation of petroleum pollutants and some may be utilized in commercial production of single cell protein (SCP) from hydrocarbons. However, their draw back lies in the fact that certain hydrocarbon utilizing organisms can cause spoilage of hydrocarbon products such as fuels. Hydrocarbon metabolism is strictly aerobic and appears always to involve the introduction of oxygen into the molecule in a process requiring a monooxygenase (= hydroxylase) or dioxygenase.
Aliphatic hydrocarbons which are straight chain paraffins (n-alkanes) can be utilized by bacteria like strains of Acinetobacter, Corynebacterium, Mycobacterium, Nocardia, Pseudomonas, by yeasts as species of Candida and the mycelial fungi Aspergillus, Botrytis, Fusarium, Helminthosporium, Hormoconis, and Penicillium. Some organisms can use only short-chain alkanes, some can use only long-chain alkanes.
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However, in most cases n-alkane metabolism appears to occur by co-oxidation (is read as omega oxidation), i.e. terminal methyl group of the alkane is oxidized by a monooxygenase to form a primary alcohol which is in turn oxidized via the aldehyde to the corresponding fatty acid by alcohol dehydrogenise and aldehyde dehydrogenase activities; the fatty acids then can be degraded by conventional fioxidation.
In Pseudomonas strains the alkane-oxidizing enzyme system is complex, involving w-monooxygenase a rubredoxin, and an NADH-rubredoxin oxidoreductase. In eukaryotes and probably in some bacteria like Acinetobacter strains H2 alkane monooxygenase is linked to the cytochrome P-450 electron carrier systems. Branched-Chain alkanes (alkylalkanes) and unsaturated hydrocarbons (alkenes, olefins) are generally somewhat less susceptible to microbial degradation in comparison to n-alkanes. They may be oxidised in the same way as n-alkanes but alkenes may not be oxidised at the double bond resulting in the formation of a diol.
Since alkane metabolism occurs intracellularly, the hydrocarbon must be taken into the cell. Uptake may take place by different mechanism in different organisms and at least in some cases may need prior emulsification of the hydrocarbon by an extracellular bio-surfactant or bio-emulsifier. Alicyclic hydrocarbons (Cycloparaffins and cycloalkanes) are cyclic, non-aromatic hydrocarbons. They are cyclic, non-aromatic hydrocarbons. They are generally less susceptible to microbial attack in comparison to either aliphatic or aromatic compounds. Degradation of cyclohexane by strains of Nocardia or Pseudomonas involves oxidation of the cyclohexane to cyclohexanol by a cyclohexane monoxygenase.
Cyclohexanol is oxidised to cyclohexane and then an oxygen atom is introduced into the ring (forming a lactone) by cyclohexanone monoxygenase. The lactone, then can be hydrolysed to form a non-cyclic dicarboxylic acid. Aromatic hydrocarbons (benzene, naphthalene, anthracene etc.) are present in the petroleum and are formed by incomplete combustion of almost any organic material.
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They are thus common pollutants and many are recognized carcinogens. Pseudomonas spp of bacteria metabolise aromalic hydrocarbons by initially incorporating two atoms of oxygen into the substrate to form a c/s-dihydrodiol; and this reaction catalysed by a multicomponent enzyme system comprising of dioxygenase, a flavoprotein and iron sulphur proteins.
The c/s-dihydrodiol is oxidized to a catechol which is in turn a substrate for another dioxygenase system that breaks open aromatic ring. The fungi, in contrast, oxidize aromatic hydrocarbons using a cytochrome P-450 dependent monoxygenase to form a reactive arene oxide. This is turn can either undergoes isomerization to form a monohydric phenol, or may be hydrolysed enzymatically to result into a trans-dihydrodiol.
