# Potential Use of Carrageenanans against the Limestone Proliferation of the Cyanobacterium
###### Abstract  
Stone biodeterioration by cyanobacteria is a common issue in the field of cultural heritage. As they are considered the first stone colonizers, the need to control their growth has increased. In this study, we evaluated the effectiveness of kappa/iota carrageenanans from the red seaweed _Chondracanthus teedei_ var. _lusitanicus_ against the limestone proliferation of the cyanobacterium _Parakomarekiella sesanandensis_, under laboratory conditions. For this purpose, 200 uL of kappa/iota carrageenanans (0.01 g mL\({}^{-1}\)) were applied into the surface of the limestone replicas prior to their inoculation with _P. sesanandensis_. Results were evaluated after 4 months of incubation through visual inspection, stereomicroscopy, scanning electron microscopy and colorimetric analyses. The gathered data demonstrated that these types of carrageenanans have the potential to reduce the colonization of _P. sesanandensis_. With one sole application, the aesthetical alterations caused by the proliferation of _P. sesanandensis_ were drastically reduced. This study highlights the need to explore marine-based products, particularly those derived from seaweeds with antimicrobial properties, as alternative methods for biocleaning cultural heritage assets. bibliography; carrageenanans; cyanobacteria; limestone; natural compounds; seaweeds 2021 11 1089 10 10 2021 11 10  
proliferation of harmful microorganisms on stone monuments, control and prevention procedures are often employed with the ultimate goal of accomplishing a good state of conservation. However, the majority of these procedures often involve the use of chemicals (biocides) that might cause even more damage to the substrata and/or do not produce long-lasting results, in addition to their potential negative impact in terms of environment and human health [10; 11; 12]. For this reason, there is an increased interest in the use of more eco-friendly, long-lasting and cost-effective treatments based on natural products derived from microorganisms and plants [11; 12]. Some recent studies have already demonstrated the use of natural compounds against colonization of stone monuments by phototrophic microorganisms in the field of cultural heritage [11; 13; 14]. Nevertheless, as progress with the use of natural compounds as biocide treatments has been made, to the best of our knowledge, there are still a variety of products, particularly marine-derived compounds, largely unexplored in cultural heritage studies. Carrageenan are sulfated polysaccharides that are found in the cell walls of red seaweeds [15] and are known to possess a variety of biological properties, including antioxidant, anti-inflammatory, antiviral, antibacterial and antifungal activities [16; 17; 18]. Chemically, these polysaccharides are composed of galactose and possess a high content of sulfate esters [19], albeit distinct variations usually occur. In fact, carrageenanans are normally classified based on distinct features, including the number and position of sulfate groups, the presence of presence of 3,6-anhydro-d-galactose and the conformation of the pyranose ring [20]. The most common types of carrageenanans are \(\kappa\) (kappa), \(\iota\) (iota) and \(\lambda\) (lambda): kappa-carrageenanans have alternating (1-3)-\(\beta\)-d-galactose-4-sulfate and (1-4)-3,6-anhydro-\(\alpha\)-d-galactose units, while iota-carrageenanans have an additional sulfate group on C-2(O) of the (1-4)-3,6-anhydro-\(\alpha\)-d-galactose sugars, resulting in two sulfates per disaccharide repeating unit [21]. On the other hand, lambda-carrageenanans have an additional sulfate group linked to the C-6 position of the 4-linked residue, but in turn this is a (1-4)-\(\alpha\)-d-galactopyranose. Regardless of the abundancy of these structures, instead of producing pure carrageenanans, seaweeds may produce hybrid structures such as \(\
u\) (nu), \(\mu\) (mu), \(\theta\) (theta), \(\beta\) (beta) and \(\xi\) (xi).