High-throughput sequencing of the 16S rRNA V4 regions revealed that the most abundant bacterial phyla of the shipwreck samples were Firmicutes and Proteobacteria, which were found in all of the samples. The Firmicutes genera Gracilibacillus and Alicyclobacillus were present in all samples and are often associated with earthy and drought environments but have also been detected on salt-degraded monuments15,16. Gracilibacillus are halotolerant bacteria that may not be able to degrade cellulose but can produce xylanases17. Proteobacteria was the other dominant bacterial phylum and was represented by the genera Marinobacter, Halomonas and Azoarcus. Marinobacter are frequently identified as hydrocarbon-degrading organisms in a wide variety of marine environments, including lignin-enriched environments18. Halomonas are halophiles that require high NaCl concentrations for growth. Halomonas are highly versatile and can successfully grow in a variety of temperature and pH conditions and, importantly, produce cellulases and xylanases19,20. Azoarcus are usually found in contaminated water, as they are involved in the degradation of some contaminants, commonly living in soil21. Thus its presence on the ship might be associated with the contaminants of sea water. The other bacterial phyla that were found, Bacteroidetes, Actinobacteria, Chloroflexi, Acidobacteria, and Gemmatimonadetes, are all also frequently detected in cultural heritage artefacts and humid environments22.