Assessment of the bacterial community structure in shallow and deep sediments of the Perdido Fold Belt region in the Gulf of Mexico

PeerJ. 2018 Sep 13;6:e5583. doi: 10.7717/peerj.5583. eCollection 2018.


The Mexican region of the Perdido Fold Belt (PFB), in northwestern Gulf of Mexico (GoM), is a geological province with important oil reservoirs that will be subjected to forthcoming oil exploration and extraction activities. To date, little is known about the native microbial communities of this region, and how these change relative to water depth. In this study we assessed the bacterial community structure of surficial sediments by high-throughput sequencing of the 16S rRNA gene at 11 sites in the PFB, along a water column depth gradient from 20 to 3,700 m, including five shallow (20-600 m) and six deep (2,800-3,700 m) samples. The results indicated that OTUs richness and diversity were higher for shallow sites (OTUs = 2,888.2 ± 567.88; H' = 9.6 ± 0.85) than for deep sites (OTUs = 1,884.7 ± 464.2; H' = 7.74 ± 1.02). Nonmetric multidimensional scaling (NMDS) ordination revealed that shallow microbial communities grouped separately from deep samples. Additionally, the shallow sites plotted further from each other on the NMDS whereas samples from the deeper sites (abyssal plains) plotted much more closely to each other. These differences were related to depth, redox potential, sulfur concentration, and grain size (lime and clay), based on the environmental variables fitted with the axis of the NMDS ordination. In addition, differential abundance analysis identified 147 OTUs with significant fold changes among the zones (107 from shallow and 40 from deep sites), which constituted 10 to 40% of the total relative abundances of the microbial communities. The most abundant OTUs with significant fold changes in shallow samples corresponded to Kordiimonadales, Rhodospirillales, Desulfobacterales (Desulfococcus), Syntrophobacterales and Nitrospirales (GOUTA 19, BD2-6, LCP-6), whilst Chromatiales, Oceanospirillales (Amphritea, Alcanivorax), Methylococcales, Flavobacteriales, Alteromonadales (Shewanella, ZD0117) and Rhodobacterales were the better represented taxa in deep samples. Several of the OTUs detected in both deep and shallow sites have been previously related to hydrocarbons consumption. Thus, this metabolism seems to be well represented in the studied sites, and it could abate future hydrocarbon contamination in this ecosystem. The results presented herein, along with biological and physicochemical data, constitute an available reference for further monitoring of the bacterial communities in this economically important region in the GoM.

Keywords: 16S rRNA; Bacterial diversity; Gulf of Mexico; Perdido Fold Belt.

Grants and funding

This research was provided by “Biotechnology of marine organisms” awarded by the National Council of Science and Technology of Mexico (CONACYT) project 15689 - 2014 and by the Marine Resources Department at CINVESTAV Merida. CONACYT awarded Ma. Fernanda Sánchez-Soto Jiménez with Master and PhD Scholarships. The necessary infrastructure to complete this investigation came from CONACYT –Mexican Ministry of Energy –Hydrocarbon Trust, project 201441; and from CONACYT 251622 - 2015 received by José Q. García-Maldonado. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.