Structure and composition of microbial communities in the water column from Southern Gulf of Mexico and detection of putative hydrocarbon-degrading microorganisms.

This study assessed the bacterioplankton community and its relationship with environmental variables, including total petroleum hydrocarbon (TPH) concentration, in the Yucatan shelf area of the Southern Gulf of Mexico. Beta diversity analyses based on 16S rRNA sequences indicated variations in the bacterioplankton community structure among sampling sites. PERMANOVA indicated that these variations could be mainly related to changes in depth (5 to 180 m), dissolved oxygen concentration (2.06 to 5.93 mg L-1), and chlorophyll-a concentration (0.184 to 7.65 mg m3). Moreover, SIMPER and one-way ANOVA analyses showed that the shifts in the relative abundances of Synechococcus and Prochlorococcus were related to changes in microbial community composition and chlorophyll-a values. Despite the low TPH content measured in the studied sites (0.01 to 0.86 µL L-1), putative hydrocarbon-degrading bacteria such as Alteromonas, Acinetobacter, Balneola, Erythrobacter, Oleibacter, Roseibacillus, and the MWH-UniP1 aquatic group were detected. The relatively high copy number of the alkB gene detected in the water column by qPCR and the enrichment of hydrocarbon-degrading bacteria obtained during lab crude oil tests exhibited the potential of bacterioplankton communities from the Yucatan shelf to respond to potential hydrocarbon impacts in this important area of the Gulf Mexico.

Effects of a Light Crude Oil Spill on a Tropical Coastal Phytoplankton Community.

Oiling scenarios following spills vary in concentration and usually can affect large coastal areas. Consequently, this research evaluated different crude oil concentrations (10, 40, and 80 mg L-1) on the nearshore phytoplanktonic community in the southern Gulf of Mexico. This experiment was carried out for ten days using eight units of 2500 L each; factors monitored included shifts in phytoplankton composition, physicochemical parameters and the culturable bacterial abundance of heterotrophic and hydrocarbonoclastic groups. The temperature, salinity, and nutrient concentrations measured were within the ranges previously reported for Yucatan Peninsula waters. The total hydrocarbon concentration (TPH) in the control at T0 indicated the presence of hydrocarbons (PAHs 0.80 µg L-1, aliphatics 7.83 µg L-1 and UCM 184.09 µg L-1). At T0, the phytoplankton community showed a similar assemblage structure and composition in all treatments. At T10, the community composition remained heterogeneous in the control, in agreement with previous reports for the area. However, for oiled treatments, Bacillariophyceae dominated at T10. Hydrocarbonoclastic bacteria were associated with oiled treatments throughout the experiment, while heterotrophic bacteria were associated with control conditions. Our results agreed with previous works at the taxonomic level showing the presence of Bacillariophyceae and Dinophyceae in oil-related treatments, where these groups showed the major interactions in co-occurrence networks. In contrast, Chlorophyceae showed the key node in the co-occurrence network for the control. This study aims to contribute to knowledge on phytoplankton community shifts during a crude oil spill in subtropical oligotrophic regions.

Changes in the Bacterioplankton Community Structure from Southern Gulf of Mexico During a Simulated Crude Oil Spill at Mesocosm Scale.

The southern Gulf of Mexico (sGoM) is highly susceptible to receiving environmental impacts due to the recent increase in oil-related activities. In this study, we assessed the changes in the bacterioplankton community structure caused by a simulated oil spill at mesocosms scale. The 16S rRNA gene sequencing analysis indicated that the initial bacterial community was mainly represented by Gamma-proteobacteria, Alpha-proteobacteria, Flavobacteriia, and Cyanobacteria. The hydrocarbon degradation activity, measured as the number of culturable hydrocarbonoclastic bacteria (CHB) and by the copy number of the alkB gene, was relatively low at the beginning of the experiment. However, after four days, the hydrocarbonoclastic activity reached its maximum values and was accompanied by increases in the relative abundance of the well-known hydrocarbonoclastic Alteromonas. At the end of the experiment, the diversity was restored to similar values as those observed in the initial time, although the community structure and composition were clearly different, where Marivita, Pseudohongiella, and Oleibacter were detected to have differential abundances on days eight-14. These changes were related with total nitrogen (p value = 0.030 and r2 = 0.22) and polycyclic aromatic hydrocarbons (p value = 0.048 and r2 = 0.25), according to PERMANOVA. The results of this study contribute to the understanding of the potential response of the bacterioplankton from sGoM to crude oil spills.