keywords: Paint, oxalic acid, painted wall, xanthan gum, HPLC, biodeterioration
Biodeterioration of painted walls by organisms producing various organic acids leads to undesirable loss of aesthetics. The potential of these organisms to utilize xanthan gum, a paint rheology modifier as sole carbon source for oxalic acid production was investigated. Fourteen (14) organisms isolated from grossly biodeteriorated painted walls in Lagos, Nigeria were identified to be species of the genera Bacillus, Paenibacillus, Aspergillus and Penicillium using the Sanger sequencing of the 16S rRNA gene for bacteria and the Internal Transcribed Spacer (ITS) DNA in the rRNA operon for fungi. The bacterial population ranged from 3.00 x 103 to 2.63 x 104CFU/g while the fungal population ranged from 1.00 x 103 to 1.63 x 104 SFU/g, respectively. HPLC analysis confirmed that all isolates produced oxalic acid ranging from 2.69 to 19.0447 mg/g. Descriptive statistical analysis of mean concentration of oxalic acid produced shows that Bacillus litoralis strain CECRI-26/07 was the highest producer on the average, while Paenibacillus azoreducens strain DW-TSB-4 was the lowest. Optimization studies of B. litoralis strain CECRI-26/07, showed 370C and pH 6 as optimal producing conditions. Higher level of discoloration due to oxalic acid production is expected in the tropics by virtue of the prevailing environmental condition of 370C which supports optimal growth of B. litoralis strain CECRI-26/07, a major culprit in the discoloration process.