Beneficial bacteria-based bioformulations as potential biocontrol and biocleaning solutions for stone heritage conservation.

Indigenous bacterial community of the deteriorated Rožanec Mithraeum monument (Slovenia) was analyzed as a basis for development of a synergistic bacterial consortium with potential to be re-introduced for biocontrol and biocleaning treatment of infested limestone monument. Core community constituents, based on the 16S rRNA gene sequences metabarcoding analysis, were representatives of Proteobacteria, Actinobacteriota, and Cyanobacteria phyla. Bacteria of Bacillus and Paenibacillus genera dominated in the culturable bacterial community. The most extensive enzymatic potential, as a foundation of biocleaning process, was observed for Bacillus mycoides MIT8.7 and Paenibacillus amylolyticus/taichungensis/tylopili/tundrae MIT8.18. In general, representatives of Bacillus genus demonstrated excellent amylase and protease potential, with small lipase, cellulase, mannanase, and xylanase activity. The highest PGI% values, against 7 autochthonous biodeteriogenic fungi, were measured for Bacillus velezensis MIT7.8 and Pseudomonas chlororaphis subsp. aurantiaca MIT4.11 highlighting them as the most promising bacterial antagonist for the consortium. Compared to commercial biocides 0.3% Preventol RI80, 100% Keim, and 100% BFA, recommended for application in stone conservation, Streptomyces anulatus 1-3 TSA and Streptomyces sp. 11-11MM full cultures also proved efficient and lacked any corrosive effect as reflected in unaltered surface roughness parameters Rq and Ra, over the 3 months application period on laboratory models made of limestone obtained in the proximity of the Rožanec Mithraeum relief. Characterized bacterial candidates possess potential to be used for development of a bacterial consortium that can be utilized in situ as a natural, environment friendly, and safe alternative effective in the conservation of stone heritage via joint activity making an important step towards desired widespread exclusion of biocide application.