Heterologous Expression and Purification of a 238 kDa Large Biofilm Associated Surface Protein (Bap) in Escherichia coli

Staphylococcus aureus is one of the most common root causes of nosocomial infections because of its dominant biofilm forming property. Staphylococci infection is common in both humans and animals. Biofilms have been implicated in almost 60% of all bacterial infections [1]. The bacterial biofilm formation is governed by several factors that are under the control of diverse genetic elements [2]. One of the factors is the expression of Biofilm-associated protein which confers the capacity to form biofilm. It also plays a crucial role in bacterial infection process even in the absence of ica operon, which is responsible for polysaccharide intercellular adhesion (PIA)/polyβ-1,6-N-acetylglucosamine (PNAG) synthesis [3]. Bap was the first protein among the family of large surface proteins that is reported to be involved in initial attachment to surfaces and assist in cell–cell interactions [4]. The gene bap has been reported to be widespread among natural isolates of coagulase-negative Staphylococcus species, like S. epidermidis, S. chromogenes, S. xylosus, S. simulans and S. hycus [5]. Of late, a number of surface proteins are reported to have structural homology with bap and constitute Biofilm-associated proteins family (Bap family). Such proteins have been identified in different organisms’ viz., Bap in Staphylococcus aureus, Esp in Enterococcus faecalis [6], LapA in Pseudomonas putida [7] and BapA in Salmonella [8]. Common features of member proteins of this family are an extracellular signal sequence, very high molecular weight, repetitive structure and a typical cell wall anchoring domain [4]. In the recent past, there is an increase in the list of biofilm associated surface proteins in the NCBI database despite not knowing the physical basis of function. Therefore, it is necessary to decode how actually these proteins perform in their adhesive functions.