Evaluation of the ability of alkalophilic bacteria to form a biofilm on the surface of Portland cement-based mortars

Abstract

This paper investigates bacteria colonisation through biofilm formation, based on the premise that biofilm helps bacteria to have a better development. The aim is to homogenize bacterial growth on recycled concrete aggregates (RCA) to obtain a homogeneous precipitation of calcium carbonate (CaCO3). In previous studies, Bacillus halodurans C-125 was selected to perform biocarbonation on RCA to generate a coat of CaCO3 and diminish water absorption. Contrary to expectations, its poor development led to an heterogeneous CaCO3 precipitation, resulting in an inefficient treatment. Within the framework of this criterion the genetic information of B. halodurans C-125 was compared with a homologous specie “Bacillus subtilis str. 168” to know if it possessed the genes to encode Tas A and Tap A proteins. These proteins consolidate a robust biofilm in Bacillus subtilis str. 168, which promotes bacterial development and adhesion to a surface. Remarkably, B. halodurans C-125 lacks the genes to produce Tas A and Tap A. B. halodurans C-125 was also compared with a group of bacteria isolated from RCA to produce biofilm on MSgg media. Curiously, B. halodurans C-125 did not form a robust biofilm while the bacteria isolated from RCA did. Because of the capacity of the isolated bacteria to form biofilm, they were inoculated on a mortar disk with nutrient and MSgg broth. The results showed traces of bacterial development and precipitation of CaCO3 in form of calcite.