## 3 Results and Discussion  
### Microbial Isolates  
In our former work [36], we established TBNPA and DBNPG enrichment cultures in which total of nine strains were isolated in the current study (five and four isolates for each consortium, respectively; Table 1). Two strains of _Pseudomonas citronellolis_ were found in both groups of isolates. When amended with a carbon source (yeast extract/100 mg L\({}^{-1}\) glucose) and TBNPA or DBNPG, all nine individual strains exhibited growth but no TBNPA or DBNPG degradation. Different strain combinations originating either in the TBNPA or DBNPG enrichment culture were tested for degradation. DBNPG and TBNPA degradation occurred only with a combination of the four isolates from the DBNPG enrichment culture, strains DB2-DB5, and an additional carbon source (screening and degradation experiments to determine this strain combination are described in the Supplementary Materials). Therefore, these \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**ID**} & \multirow{2}{*}{**Strain (Highest Similarity, 99\%)**} & **Gene Bank** & **OD 600 (Initial** \\  & & **Accession Number** & **Density CFU/mL)** \\ \hline DB2 & _Pseudomonas citronellolis_ & K7229738 & 0.001 (1.10 \(\times\) 10\({}^{5}\)) \\ \hline DB3 & _Gardonia siltwensis_ & K7229739 & 0.001 (1.70 \(\times\) 10\({}^{5}\)) \\ \hline DB4 & _Shitella zooglooides_ & K7229740 & 0.004 (4.90 \(\times\) 10\({}^{5}\)) \\ \hline DB5 & _Microbacteriumium oxydans_ & K7229741 & 0.027 (3.00 \(\times\) 10\({}^{6}\)) \\ \hline TB1 & _Pseudomonas aeruginosa_ & K7229734 & \\ \hline TB2 & _Delftia sturhutensis_ & K7229735 & \\ \hline TB3 & _Pseudomonas citronellolis_ & K7229736 & \\ \hline TB4 & _Sphingobacterium siyangense_ & K7229752 & \\ \hline TB5 & _Microbacterium paraoxydans_ & K7229753 & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Strain ID used in experiments with identified genus and species with initial density given for the four-strain consortium, which was seen able to degrade both TBNPA and DBNPG. four strains were used for all subsequent experiments. In the formerly established DBNPG enrichment culture, from which the strains were isolated [36], DB2-DB5 were observed in varying abundances (data derived from Illumina MiSeq sequencing). _Gordonia siltwensis_ (DB3) and _Microbacterium oxydans_ (DB5), belonging to the _Actinomycetales_ order, appeared at a relatively low abundance at <2% in both TBNPA and DBNPG enrichments. _Pseudomonas_ (DB2), on the other hand, is relatively abundant in the TBNPA enrichment (29.3%), while in the DBNPG enrichment, it was only 7.4%. _Shinella zoogloeoides_ (DB4), belonging to the _Betaproteobacteria_ class, showed an opposite trend, i.e., high in the DBNPG enrichment (21%) and low in the TBNPA enrichment (3%). These isolates can most likely catalyze an oxidative mechanism involving a mono or dioxygenase, as was previously demonstrated [36]. In addition, several monooxygenases have been identified previously in strains similar to each of the four isolates, pointing to their potential in TBNPA and DBNPG oxidation [40; 41; 42; 43; 44; 45; 46]. For example, _Pseudomonas citronellosis_ UAM-Ps1 co-metabolically transforms methyl tert-butyl ether (MTBE) to tert-butyl alcohol with n-pentane or n-octane as a gratuitous inducer of alkane hydroxylase (AlkB) [47]. In our study, it was unclear which of the strains was directly involved in the degradation of the compounds. The necessity to incubate all four strains to facilitate the degradation of DBNPG and TBNPA implies that some form of syntrophic relationship exists between the four strains. Syntrophic relationships between bacteria may be in the form of (1) metabolic complementation, in which the degrading bacteria depend on auxiliary strain/s that provide nutrients and growth factors or remove toxic metabolites, or (2) associated metabolism, in which all consortium members utilize metabolites through cross feeding [48].