Bioemulsifier (BE-AM1) produced by Solibacillus silvestris AM1 is a functional amyloid that modulates bacterial cell-surface properties

Abstract

A novel estuarine bacterial strain, Solibacillus silvestris AM1, produces an extracellular, thermostable and fibrous, glycoprotein bioemulsifier (BE-AM1). The amyloid nature of the bioemulsifier (BE-AM1) was confirmed by biophysical techniques (Congo red based polarization microscopy, ThioflavinS based fluorescent microscopy, fibrous arrangement in transmission electron microscopy and secondary structure measurement by FTIR and CD spectrum analysis). Cell-bound BE-AM1 production by S. silvestris AM1 during the mid-logarithmic phase of growth coincided with a decrease in cell surface hydrophobicity, and an increase in cell autoaggregation and biofilm formation. It was observed that the total interfacial interaction energy ([Formula: see text]) for the surface of the bioemulsifier producing S. silvestris AM1 and different derivatized surfaces of polystyrene (silanized and sulfonated) was found to support biofilm formation. This study has revealed that the BE-AM1, a bacterial bioemulsifier, is a functional amyloid and has a role in biofilm formation and cell surface modulation in S. silvestris AM1.

Characterization of Solibacillus silvestris strain AM1 that produces amyloid bioemulsifier

“…S. silvestris AM1 produces its amyloid bioemulsifier as reported earlier after 4th hour in the cell‐bound phase and after 12th hour as cell‐free phase. It was also seen that the cell‐bound amyloid bioemulsifier BE‐AM1 production was restricted to exponential phase of bacterial growth and cell‐free phase with stationary growth of bacterium.…”

“…S. silvestris AM1, produced amyloid BE‐AM1 in isolation medium (ZM) than in other reported medium that is, there was less or no amyloid BE‐AM1 in reported production medium like Pfiffner et al, Cooper and Goldenberg, Gurjar et al, Yun and Park, Suthar et al with or without change in carbon sources (data not given). It has been reported earlier that S. silvestris AM1 produced BE‐AM1 amyloid bioemulsifier in presence of only Zobel Marine (ZM) medium. ZM medium, formulated in early 20th century is the only medium available for studying marine heterotrophic bacteria without the recurrent need for sea water and strain AM1 was found to produce BE‐AM1 only in this medium.…”

“…Amyloid proteins are extremely resistant to most enzymes, thermal and chemical denaturants due to their quaternary structure of β‐sheets stacked perpendicular to fibrillar axis as seen in the amyloid bioemulsifier of S. silvestris AM1 . The BE‐AM1 protein bioemulsifier is a surface protein in S. silvestris AM1 as seen in other microbial functional amyloids reported‐ fungal Hydrophobins , actinomycete Chaplins , bacterial Curli ( E. coli ), aggregative fimbriae − thin aggregative fimbriae (or Tafi in Salmonella ), Fap amyloids ( Pseudomonas aeruginosa ) and Tas proteins ( Bacillus ) have been well studied . Functional bacterial amyloids are known to perform various roles in strengthening cell surface interactions such as adhesion, aggregation, and biofilm formation , function as toxins and protect against host defenses and playing a vital role in animal infections .…”

In Silico Analysis of Bacterial Functional Amyloids and their Interactions

“…Microbial functional amyloids, since their discovery in late 1980s [10], similar proteins have been reported from a number of microorganisms [6]. Majority of these reported functional amyloids are from Proteobacteria, Actinobacteria, Firmicutes and Bacteroides but only a few of them have been purified and investigated in depth.…”

“…This cellular toxicity of amyloids is avoided in bacteria by using dedicated and highly controlled pathway for assembling amyloids and extracellular assembly of these proteins. Thus by nullifying the cytotoxic effects of amyloids, they can be used as stable protein structures for many different functions [4], [6]. Only few bacterial species important in relation to human infections have been studied with respect to FuBA with curli like fibrils.…”