## 2 Results and Discussion
### Organic Compound Degradation and Biosurfactant Production
#### 2.8.2. Degradation of Aromatic Hydrocarbons  
Aromatic compounds are both common growth substrates for microorganisms and prominent environmental pollutants [101]. These structurally diverse compounds are independently converted into a small number of structurally simpler common intermediates, such as catechol and protocatechuate [102]. The \(\beta\)-ketoadipate pathway is present in many bacterial groups, including gram-positive and gram-negative bacteria, and is considered one of the most widely distributed sets of genes for the degradation of aromatic compounds in microbes. This central pathway is composed of two ortho-cleavage branches, one for degradation of protocatechuate (_pca_ genes) and the other for degradation of catechol (_cat_ genes) [103]. Both protocatechuate and catechol are central metabolites derived from the oxygenation of different phenolic compounds, lignin monomers and polyaromatic hydrocarbons [104]. The final products of both pathways are acetyl-CoA and succinyl CoA [105]. It is worth noting that the protocatechuate branch of the \(\beta\)-ketoadipate pathway is ubiquitous in completely sequenced _Pseudomonas_ genomes [28], emphasizing the importance of aromatic compound catabolism by these bacteria. Genome analysis of  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Gene** & **Accession Number** & **KO Numbers** & **Gene Product** & **Activity** \\ \hline _paaH_ & MBG8559350.1 & K00074 &
\begin{tabular}{c} 3-hydroxybutyl-coa dehydrogenase \\ (EC:1.1.1.157) \\ _paaI_ \\ _paaK_ \\ _paaA_ \\ _paaB  
the ZCR6 strain revealed the presence of the _pca_ cluster encoding enzymes engaged in protocatechuate catabolism but a lack of _cat_ clusters. Furthermore, in the genome of the ZCR6 strain, the _lpqa_ genes of the homoprotocatechuate catabolic pathway were identified (Table 8). Homoprotocatechuate (3,4-dihydroxyphenylacetic acid HPC) is meta-cleaved by an HPC 2,3-dioxygenase encoded by the _lpqaD_ gene. The product 5-carboxymethyl-2-hydroxymuconic semialdehyde (CHMS) is then converted to 5-carboxymethyl-2-hydroxy-muconic acid (CHM) and subsequently degraded by the _lpqaF_, _lpqaG_, _lpqH_ and _lpqal_ gene products into Krebs cycle intermediates [106]. The _pua_ cluster encoding enzymes involved in the phenylacetyl-CoA pathway was also present in the genome of the ZCR6 strain (Table 8). This pathway constitutes a catabolism through which many other structurally related compounds, such as phenylethylamine, phenylethanol, styrene, tropate, and n-phenylalkanoates with an even number of carbon atoms, are funneled [103]. Moreover, the ZCR6 strain contained genes for catabolism of ethylbenzene (_etbAa and ethAb_) and naphthalene (_nagZ_). During the biodegradation of hydrocarbons, the bioavailability of these compounds is considered a key limiting factor due to their low aqueous solubility and high hydrophobicity. To enhance the bioavailability of hydrocarbons, microorganisms produce biosurfactants [107; 108]. The biosurfactants produced by bacteria can also contribute to inhibiting the growth of phytopathogens, help colonize plant tissues and improve bacterial motility [109]. In this study, the ZCR6 strain produced a surface-active compound, which showed a positive result for the oil-spreading test and exhibited emulsification activities against _p_-xylene (E24 = 71.43% \(\pm\) 1.43), diesel oil (E24 = 14.71% \(\pm\) 0.29) and _n_-hexadecane (E24 = 25.71% \(\pm\) 0.57) (Table 1). These results suggest that the ability of ZCR6 to degrade crude oil may be linked with the production of biosurfactants. For example, [PERSON] et al. [110] reported that _Pseudomonas aeruginosa_ ZS1 isolated from petroleum sludge produced a high level of rhamnpid that effectively emulsified crude oil, accelerating its uptake and degradation. Literature data indicate that members of the genus _Pseudomonas_ possess robust metabolic machinery with the inherent ability to produce multiple and diverse secondary metabolites, including biosurfactants [111].