Klebsiella aerogenes and Comamonas testosteroni as bioremoval agents on graffiti-coated concrete and granite : Impact assessment through surface analysis

Klebsiella aerogenes ATCC 13048 and Comamonas sp. ATCC 700440 (here identified as Comamonas testosteroni) have previously been shown to be good candidates for graffiti bioremoval, demonstrating in both immersion and subaerial strategies high levels of tolerance to the presence of the graffiti paint and some ability to degrade the graffiti material. To explore further the graffiti bioremoval capacity by these two newly found suitable bacteria, an experiment was carried out encompassing an improved assay protocol (protocol time was reduced from 20 to 14 days). The formation of pinholes - noticeably higher on concrete than on granite - was already observable by naked eye and further proved by digital image analysis, novel to this experiment, which showed holes greater in number due to K. aerogenes and greater in size due to C. testosteroni. Complementarily, surface microtopography - also novel for bioremoval studies with bacteria - offered detailed information on surface irregularities that allows better understanding of the performance of the bacteria. In contrast, non-mapping techniques, such as wetting by droplet, specular gloss and roughness measured in line transects provided less information for the study. Infrared (ATR-FTIR) spectroscopy and colour change assessment – mainly in the achromatic parameter L* – showed more intense changes by Comamonas testosteroni.