Enhancing the culturability of bacteria present on archived audio-visual materials

Cultural heritage objects, rich with historical significance, face the persistent threat of biodeterioration, potentially resulting in irreplaceable losses. While both fungi and bacteria contribute to this process, bacterial involvement is often underrepresented in scholarly research compared to fungal studies. Although culture-independent methods provide comprehensive insights, the culture-dependent approach remains the primary approach in archive settings. Therefore, this study aims to optimise cultivation strategies to identify bacterial communities present on historical audio-visual materials stored in two Czech Republic archives, with an emphasis on enhancing captured diversity as well as numbers of colony-forming units. To accomplish this, various cultivation strategies were employed, including the use of multiple media types, prolonged cultivation time, diluted nutrient concentrations in the media, and the addition of a resuscitation-promoting factor (Rpf). Subsequent identification was conducted through either MALDI-TOF MS or Sanger sequencing. A total of 759 isolates, representing 26 distinct genera, were obtained, with the Bacillus and Micrococcus genera emerging as the most prevalent. The use of multiple media significantly increased the diversity of captured bacteria, with only 10 % and 20 % of genera shared across all media in the Trebon and Brno archives, respectively. The addition of Rpf enabled the capture of several additional genera, mostly from the Actinomycetota phylum. Additionally, distinct bacterial communities were associated with different binder types (albumen, collodion, and gelatine), with only six genera shared across all binder types, indicating metabolic versatility among these bacteria. These findings enhance our understanding of bacterial communities on audio-visual materials and underscore the importance of diverse cultivation strategies in capturing a comprehensive picture of microbial diversity in archival settings.