Influence of bacterial biopolymers on physical properties of experimental limestone blocks

This article describes the consolidation effects of bacterial biopolymers synthesized by biofilm bacteria colonizing Mayan limestone buildings on the surface properties of limestone blocks, including disaggregation, hardness, and total color change at the laboratory level. The biopolymers evaluated, produced by bacterial isolates TM1B-488, TM1B-489, TM1B-349, and TM1B-464, influenced surface properties at different levels. 16S rRNA gene sequences analysis showed that isolate TM1B-349 was related with Psychrobacter sp. strain Marseille P-5312, TM1B-464 was related with Agrococcus terreus strain BT116, and isolates TM1B-488 and TM1B-489 were related with Xanthomonas citri pv. mangiferaeindicae strain XC01. Biopolymer A reduced the surface disaggregation of the material (26%) compared to the untreated control, as revealed by the peeling test, followed by biopolymer B (10%), while the remaining biopolymers had a negligible effect. The cactus biopolymer reduced disaggregation at higher levels (37%). On the other hand, there was a similar concomitant increase in surface hardness of limestone samples coated with biopolymer A (34%) and biopolymer B (32%), higher than biopolymers C (10%) and D (19%). Total color change for all treatments was below the threshold value of 5, indicating a non-significant color alteration. Partial chemical characterization of best-performing biopolymer (A) suggests its probable glycoprotein nature, whose constitutive acidic monosaccharides probably contributed to higher adherence to the limestone surfaces, contributing to surface stabilization, hardening the surface, and decreasing surface decohesion. These preliminary findings suggest its potential application in bioconsolidants, but further studies are required.