Degradation of phenolic compounds by the yeast Candida tropicalis HP 15 I. Physiology of growth and substrate utilization
✍ Scribed by M. Krug; H. Ziegler; Dr. G. Straube
- Publisher
- John Wiley and Sons
- Year
- 1985
- Tongue
- English
- Weight
- 395 KB
- Volume
- 25
- Category
- Article
- ISSN
- 0233-111X
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✦ Synopsis
The yeast Cnndida tropicalis HP 15 was able to utilize phenol up to concentrations of 2.5 g/l as a sole carbon and energy source. Phenol was metabolized via the ,B-kctoadipate pathway by an inducible enzyme system.
Besides phenol, resorcinol, quinol, hydroxyquinol, catechol, and to a lesser extend 4-chlorocatechol, protocatechuate, p-cresol, m-chlorophenol, and p-chlorophenol were metabolized by the yeast. A total of 30 aromatic compounds were tested as substrates.
Phenolic compounds are widely distributed in nature and phenol and its derivatives belong to the toxic chemical pollutants of industrial origin. However, some microorganisms are able to utilize phenolic compounds as a sole carbon and energy source (see reviews of CHAPMAN 1972, STANIER and ORNSTON 1973, or NEUJAHR 1978). The aerobic degradation pathways in bacteria and yeasts involve the occurrence of dihydric phenols as substrates of ring-cleaving enzymes. So the first step of phenol degradation is a hydroxylation of phenol t o catechol. Catechol can undergo fission either by an intradiol or an extradiol type of cleavage ( 0 -or m-fission). This is shwon in Fig. 1. o-Fission gives rise to cis, cis-muconic acid which is converted by further enzymatic steps via 0-ketoadipate to succinate and acetyl-CoA. These products enter the central metabolism of the cell. m-Fission leads t o 2-hydroxymuconic semialdehyde and further t o formate, acetaldehyde, and pyruvete.
We are investigating the degradation of phenol and its derivatives by the yeast Candida tropicalis HP 15 which is able to utilize phenolic compounds as sole carbon and energy source via the p-ketoadipate pathway.
Methods
The yeast strain Candida tropicalie HP 15 was taken from the culture collection of tho Dcpartmont of Biosciences of the Martin-Luther-University Halle.
The cultivation was carried out in a mineral salt medium as used by WALKER (1973) with phenol as sole carbon source:
(NH,),SO, -3.0 g, MgSO, -7 H,O -0.7 g, NaCl -0.6 g, Ca(N03), -4 H,O 0.4 g, K,PO+ -1.0 g, K,HPO, -0.2 g, Fe-111-EDTA -1.0 mg, biotin -0.1 mg ad 1 1 distilled water or in a medium described by SCHLEGEL (1961) which contained Na,HPOp -12 H,O -9.0 g, KH,PO, -1.6 g, NH,Cl -1.0 g, MgSO, . 7 H,O -0.2 g, CaCO, -0.02 g, FeSO, -7 H,O -0.01 g, H,BO, -50 pg, CuSO, . 5 H,O -10 pg, KJ -10 pg, MnSO, 4 H,O -40 pg, ZnSO, * 7 H,O -40 pg, Na,MoO, . 2 H,O -24 pg ad 1 1 distilled water.
Cultures grown for 72 h on nutrient agar slants were inoculated into 100 ml of mineral medium supplemented with phenol for precultivation. The cultivation was also carried out in 100 ml of mineral medium on a rotary shaker a t 30 "C.