Extracellular polymeric substances from Shewanella sp. HRCR‐1 biofilms: characterization by infrared spectroscopy and proteomics

Abstract

The composition of extracellular polymeric substances (EPS) from Shewanella sp. HRCR-1 biofilms was investigated using infrared spectroscopy and proteomics to provide insight into potential ecophysiological functions and redox activity of the EPS. Both bound and loosely associated EPS were extracted from Shewanella sp. HRCR-1 biofilms prepared using a hollow-fibre membrane biofilm reactor. Fourier transform infrared spectra revealed the presence of proteins, polysaccharides, nucleic acids, membrane lipids and fatty acids in the EPS fractions. Using a global proteomic approach, a total of 58 extracellular and outer membrane proteins were identified in the EPS. These included homologues of multiple Shewanella oneidensis MR-1 proteins that potentially contribute to key physiological biofilm processes, such as biofilm-promoting protein BpfA, surface-associated serine protease, nucleotidases (CpdB and UshA), an extracellular lipase, and oligopeptidases (PtrB and a M13 family oligopeptidase lipoprotein). In addition, 20 redox proteins were found in extracted EPS. Among the detected redox proteins were the homologues of two S. oneidensis MR-1 c-type cytochromes, MtrC and OmcA, which have been implicated in extracellular electron transfer. Given their detection in the EPS of Shewanella sp. HRCR-1 biofilms, c-type cytochromes may contribute to the possible redox activity of the biofilm matrix and play important roles in extracellular electron transfer reactions.

The product of microbial uranium reduction includes multiple species with U(IV)–phosphate coordination

“…The presence of phospholipid head groups at the cell membrane outer surface provides another source of biological phosphate to which U(IV) could bind. Additionally, binding to phosphate diesters in DNA or RNA is also likely due to the reported secretion of extracellular DNA (eDNA) by strain MR-1 cells exposed to U. eDNA could be associated with the extracellular polymeric matrix present in tight association with the cells (Cao et al, 2011). In our experiments, total U concentrations in the experiments were either 0.4 or 1.0 mM, so the coordination of U(IV) to several phosphate groups likely requires a cellular source of phosphate, separate from orthophosphate found in the WLP medium.…”

Controlling electron transfer at the microbe–mineral interface

“…However, this work does not exclude a role for flavins in enhancing the rates of electron transfer under certain conditions. Indeed, it is compelling that the OMMCs have some structural features that suggest the possibility of flavin-binding domains that are within electron transfer distance of heme termini in the proteins (8,9,21 (22) in altering the environment for both OMMC and flavin? The emerging molecular structures for OMMCs should allow for detailed studies of the interaction between flavins and OMMCs using purified proteins and reconstituted proteoliposome systems that will shed light on these questions.…”

Modeling Substrate Utilization, Metabolite Production, and Uranium Immobilization in Shewanella oneidensis Biofilms

“…Recently, we demonstrated the relative contributions of bEPS, laEPS, and cells from Shewanella sp. HRCR-1 biofilms in U(VI) immobilization (Cao et al, 2011b). We found that bEPS and laEPS immobilized U(VI) through both reduction and adsorption.…”

“…EPS can either be tightly bound to the cell surface, called bound EPS (bEPS), or distributed in the surrounding environment of the cells in a more soluble form, called loosely associated EPS (laEPS) (Cao et al, 2011b). Recently, we demonstrated the relative contributions of bEPS, laEPS, and cells from Shewanella sp.…”

“…NMR effluent samples were collected, and U concentration was measured using a kinetic phosphorescence analyzer (KPA) (Brina and Miller, 1992;Cao et al, 2011b).…”