Composition and Corrosivity of Extracellular Polymeric Substances from the Hydrocarbon-Degrading Sulfate-Reducing Bacterium Desulfoglaeba alkanexedens ALDC

Abstract

Sulfate-reducing bacteria (SRB) often exist as cell aggregates and in biofilms surrounded by a matrix of extracellular polymeric substances (EPSs). The chemical composition of EPSs may facilitate hydrophobic substrate biodegradation and promote microbial influenced corrosion (MIC). Although EPSs from non-hydrocarbon-degrading SRB have been studied; the chemical composition of EPSs from hydrocarbon-degrading SRBs has not been reported. The isolated EPSs from the sulfate-reducing alkane-degrading bacterium Desulfoglaeba alkanexedens ALDC was characterized with scanning and fluorescent microscopy, nuclear magnetic resonance spectroscopy (NMR), and by colorimetric chemical assays. Specific fluorescent staining and ¹H NMR spectroscopy revealed that the fundamental chemical structure of the EPS produced by D. alkanexedens is composed of pyranose polysaccharide and cyclopentanone in a 2:1 ratio. NMR analyses indicated that the pyranose ring structure is bonded by 1,4 connections with the cyclopentanone directly bonded to one pyranose ring. The presence of cyclopentanone presumably increases the hydrophobicity of the EPS that may facilitate the accessibility of hydrocarbon substrates to aggregating cells or cells in a biofilm. Weight loss and iron dissolution experiments demonstrated that the EPS did not contribute to the corrosivity of D. alkanexedens cells.

Keywords: EPS; SRB; corrosion.

Figure 1

Desulfoglaeba alkanexedens str. ALDC forms aggregates and produces extracellular material: (a) cell aggregates formed by n-decane-amended incubations; (b) and (c) scanning electron micrographs of the biofilms surrounded by extracellular matrix.

Figure 2

Confocal images of D. alkanexedens EPS with fluorophore stains: (a) nucleic acid stain Syto 9^TM; (b) carbohydrate-binding conconavalin A and (c) overlayed image. Bacterial cells are 1–2 microns in size.

Figure 3

¹H NMR spectrum of EPS isolated from D. alkanexedens.

Figure 4

Gradient COSY spectrum illustrating the coupling between the proton attached to the anomeric carbon and the adjacent proton on the pyranose ring as well as the coupling between the pyranose ring proton at d 3.62 and the proton at d 2.10.

Figure 5

EPS chemical structure consists of two pyranose rings and a cyclopentanone moiety.

Figure 6

EPS corrosivity relative to the live cells and cultural fluid: (a) coupon weight loss; (b) corrosion rate based on the weight loss; (c) dissolved total iron.