Study of Candida aquaetextoris (sp. nov. Vallini et al., 1997)degradation ability of nonyl-phenol poly-ethoxylates

Nonylphenols are restive compounds that are able to mimic the 17-ß-estradiol and cause numerous toxic effects towards organisms and microorganisms. For these reasons, many strategies to remove them from environment have been studied and tested with different results. Their presence in the sewage treatement plants is the main problem of their environment diffusions and - on the basis of this - the best bioremediation strategy seems to be the degradation of nonylphenols directly inside the STW. For this purpose, many microorganisms capable to biotrasform nonylphenols through different metabolic pathways have been isolated from different matrices and studied for their degradation potential. C. aquaetextoris is an ascomycota isolated from a wastewater treatment plant (Italy, Tuscany) and studied mainly for its ability to biotrasform 4(1-nonyl)phenol using it as sole carbon and energy source. On the basis of these informations, the general aims of this work are: 1) to determine the taxonomic position of C. aquaetextoris in the genus Candida; 2) to study the biodegradation capability of C. aquaetextoris towards different types of nonylphenols in order to better clarify the microbial metabolism of this class of surfactants. Starting from the C. aquaetextoris 18S rDNA partial sequence were choosed seven Candida strain: C. tropicalis CBS 94, C. neerlandica CBS 434, C. viswanathii CBS 4024, C. maltosa CBS 5611, C. maltosa CBS 5612, C. sojae CBS 7871 and C. haemulonii CBS 8125. The taxonomic analysis showed the high similarity between C. aquaetextoris and C. viswanathii CBS 4024 underlining the possibility to group them into the same species. On the other hand, the microbiological tests showed that all the Candida sp. strains tested were unable to grow in presence of NP9EO or tNP as sole carbon and energy source. However, C. aquaetextoris remarked a higher resistance to the toxic effects exerted by NPs when compared with the other Candida sp. strains in different growth conditions. Eventually, chemical and microbiological analysis demonstrated that C. aquaetextoris is not capable to degrade the ethoxylate mojety or branched alkyl chain, but only n-alcane chain that are present in 4-n-NP. Also in presence of ethoxy chain-NPs degrading bacteria - isolated from STW of Prato (Italy, Tuscany) - C. aquaetextoris was unable to attack the complex alkylic chain and biotransform the phenol ring.