## 2 Materials and Methods
### Fungal Isolation and Identification  
Sediment samples were processed as described previously [24]. Briefly, fungi were initially isolated in a five-fold diluted medium. For maintenance, fungal isolates were grown on a potato dextrose agar (PDA) medium. Colony morphology and pigmentation were registered using a Nikon D3100 Digital Camera (Nikon Inc., Tokyo, Japan). In addition, to analyze the microscopic characteristics, including the hyphal shape, morphology, size of spores, and conidiogenous cells, fungi were grown on water agar (1.5% agar). Samples were processed by using the inverted block technique [25]. Imaging was carried out by DIC (Differential Interference Contrast) on a Nikon eclipse Ti-E microscope with an oil 60\(\times\) objective. Macroscopic and microscopic characteristics, as well as Taxonomic Keys [26] and the data available in MycoBank ([[http://www.mycobank.org/](http://www.mycobank.org/)]([http://www.mycobank.org/](http://www.mycobank.org/))) (accessed on 9 December 2020), were considered to reach genus-level identification. Total genomic DNA was extracted from axenic isolates with the DNEasy Plant Mini Kit (Qiagen). Sequence-based taxonomic verification was achieved through phylogenetic analyses [27] using: (1) the internal transcribed spacer (ITS) region of the nuclear ribosomal DNA ITS1-5.8 rDNA using the primer set ITS1F (5-CTTTGCATATTAGAGGAAGTA-3) [28] and ITS4 (5-TCCTCGCCTTATTGATATGC-3) [29], (2) the 18 rRNA gene using primer set NS1 (5-GTAGTCATATGCTTGTCTC-3) and NS4 (5-TTCCGCTAATTCCTTTAAAG-3) [30], and (3) the \(\beta\)-tubulin gene (benA) with primer set Bt2A (5-GCTAACCAAATCGGTGCTTTC-3) and Bt2b (5-ACCCTCAGTGTAGACCCTTGC-3) [31] and with degenerate primers LR1 (5-RRCRACAARTTCGTGCCCCG-3) and LR2 (5-AGTGAACTGGTCACCYACAC-3), newly designed to amplify another region of the \(\beta\)-tubulin gene downstream of the region amplified with primer set Bt2A and Bt2b for cases in which that primer set did not work. The PCR products were purified using a QIAquick Gel Extraction Kit and commercially sequenced by Eton Bioscience, Inc., San Diego, CA, USA.  
Consensus sequences were generated using Consed v29.0 [32; 33; 34] and compared to the GenBank Database through a BLAST search ([[http://www.ncbi.nlm.nih.gov/BLAST](http://www.ncbi.nlm.nih.gov/BLAST)]([http://www.ncbi.nlm.nih.gov/BLAST](http://www.ncbi.nlm.nih.gov/BLAST))) (accessed on 9 December 2020) using the MegaBLAST algorithm to retrieve the reference sequences for the phylogenetic analyses. Only hit sequences with a minimum coverage of 98% were considered for the analyses, pondering accessions associated with vouchers and type material (Table S2). Uncultured/environmental sample sequences were not considered for the analyses. Sequences were aligned with the software UGENE v36.1 [35] using MUSCLE [36]. Phylogenetic trees were inferred by MEGA X [37; 38] with the Maximum Likelihood (ML) algorithm, a bootstrap test of 1000 replications, and the K2+I (ITS and 18S) and K2+G and HKY+G (\(\beta\)-tubulin benA and LR1-LR2, respectively) models of nu  
Figure 1: Localization of twenty-four sampled stations in the Gulf of Mexico, nine in Coatzacoolcos, also known as the Salina basin (orange dots), and fifteen in the Perdido fold belt region (purple dots).  
cleotide substitution [39]. Initial trees for the heuristic search were obtained automatically by applying Neighbor-Joining and BioNJ algorithms to a matrix of pairwise distances estimated using the Maximum Composite Likelihood (MCL) approach and then selecting the topology with a superior log likelihood value. The sequences are available in GenBank under the accession numbers MW412481-MW412485 for the 18S, MW412490-MW412494 for the ITS, and MZ392424-MZ392428 for the \(\beta\)-tubulin sequences (Table S3).