Relative abundance of Bacillus spp., surfactant-associated bacterium present in a natural sea slick observed by satellite SAR imagery over the Gulf of Mexico

Kathryn Lynn Howe,Cayla Whitney Dean,Mahmood Shivji,Alexander Victor Soloviev,Susanne Lehner,John Kluge,William Perrie,Aurelien Tartar,Jody W Deming

doi:10.1525/elementa.268

Abstract

The damping of short gravity-capillary waves (Bragg waves) due to surfactant accumulation under low wind speed conditions results in the formation of natural sea slicks. These slicks are detectable visually and in synthetic aperture radar satellite imagery. Surfactants are produced by natural life processes of many marine organisms, including bacteria, phytoplankton, seaweed, and zooplankton. In this work, samples were collected in the Gulf of Mexico during a research cruise on the R/V F.G. Walton Smith to evaluate the relative abundance of Bacillus spp., surfactant-associated bacteria, in the sea surface microlayer compared to the subsurface water at 0.2 m depth. A method to reduce potential contamination of microlayer samples during their collection on polycarbonate filters was implemented and advanced, including increasing the number of successive samples per location and changing sample storage procedures. By using DNA analysis (real-time polymerase chain reaction) to target Bacillus spp., we found that in the slick areas, these surfactant-associated bacteria tended to reside mostly in subsurface waters, lending support to the concept that the surfactants they may produce move to the surface where they accumulate under calm conditions and enrich the sea surface microlayer.

Highlights

IntroductionUnder low wind speed conditions, organic material, including surface-active compounds (surfactants), accumulate and form sea slicks
Under low wind speed conditions, organic material, including surface-active compounds, accumulate and form sea slicks
Sites 3 and 4, which had moderate wind speeds of 5–7 m s–1 and no visible slicks, showed higher relative abundance of Bacillus spp. in the surface microlayer (SML) compared to subsurface water (SSW)

Summary

Introduction

Under low wind speed conditions, organic material, including surface-active compounds (surfactants), accumulate and form sea slicks. There are many causes for the accumulation of natural surfactants on the sea surface: build-up of organic material; terrestrial runoff (Wurl et al, 2011); oceanic features, such as convergence zones or frontal interfaces (Gade et al, 2013); high biological productivity; and sediment upwelling/resuspension (Espedal et al, 1996). Many marine organisms, including phytoplankton, zooplankton, seaweed, and bacteria, produce surfactants during various life processes (Gade et al, 2013). Bacteria produce surfactants for nutrient acquisition, hydrocarbon degradation, cell-to-cell communication, biofilm formation/inhibition, toxin isolation, and antifungal and antiviral activities (Dinamarca et al, 2013). The amount and type of surfactant produced depends on many factors, including availability of nutrients, such as nitrogen, magnesium, and potassium, as well as the environmental factors of pH, temperature, and salinity (Karanth et al, 1999)

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Conclusion