# Potential Use of Carrageenanans against the Limestone Proliferation of the Cyanobacterium
## 4 Discussion  
In this study, carrageenanrans from the female gametophyte life cycle phase of the red seaweed _Chondracanthus teedei_ var. _lusitanicus_ were applied into limestone replicas in order to evaluate their effects on the proliferation of the newly described cyanobacterium _Parakomarekiella essuandensis_, under laboratory conditions. Visual effects were inspected after 4 months of treatment application through stereomicroscope and SEM analysis. Color variations were also assessed in order to understand biofilm development and potential chromatic alterations in the stone replicas. Stone biodeterioration by cyanobacteria is a well-known problem in cultural heritage, as they are potentially one of the most aggressive stone colonizers due to their epilithic and endolithic growth abilities, promoting undesirable aesthetical discolorations as well as physicochemical alterations [3; 36]. Therefore, there has been an increased necessity to control, or even eliminate, these microorganisms from cultural heritage assets [37]. As it is well documented in the review by [PERSON] and [PERSON] [12], the use of plant- and organism-derived products has been rising in recent years in the field of cultural heritage. However, their study also reflects the almost inexistence exploitation of marine-derived products. In fact, according to the authors, only three marine-derived compounds have been used in this field, among which only one was of marine-algae origin, namely an extract from _Ceranium brotyocarpum_, which was used against phototrophic biofilms dwelling on monumental stone surfaces [38]. In previous studies, carrageenans extracts from the red seaweed _Chondracanthus teedei_ var. _lusitanicus_ were shown to exert antimicrobial properties, namely antifungal and antiviral activities [18; 32]. The results gathered in the present study highlight the antimicrobial potential of these _C. teedei_ var. _lusitanicus_ carrageenanans, expanding its usage for preventing the proliferation of _P. essuandensis_ on the surface of the limestones. Overall, this knowledge underlines the potential use of marine-derived extracts on the field of cultural heritage, particularly of sulfated-polysaccharides. One of the challenges in antimicrobial studies involves understanding the active compound and/or mechanism of action responsible for a given effect. In the study of [PERSON] et al. [38], the authors reported that the active compound regarding the seaweed _C. botryocarpum_ extract was still unknown. In our case, the carrageenanans extract from  
Figure 2: Color reflectance resulting from the biofilm development of _P. essuandensis_ on stone probes with and without carrageenannant treatment. Non-experimental designations refer to control probes under dry environment (not subjected to the experimentally controlled humid conditions). C. _tedei_ var. _lusitanicus_ is well known and has been previously characterized as a hybrid kappa/iota carrageenanans [18; 28]. Nonetheless, we are still not completely aware of its mode of action against the proliferation of _P. essandensis_ and, thus, more studies in this regard will be required. Previous studies using the same extracts showed an alteration on the hyphal morphology of two filamentous fungi--_Alternaria infectoria_ and _Aspergillus fumigatus_[18]. In their study, [PERSON] et al. [18] verified that, upon exposure to _C. tedei_ var. _lusitanicus_ carrageenanans, the hyphae of _A. infectoria_ became swollen, and the hyphae of _A. fumigatus_ became shortened and highly branched, which are phenotypic characteristics commonly triggered in response to antifungals [18; 39; 40]. In addition, these morphological alterations were also associated with variations on the cell wall components of these fungi, namely in their \(\beta\)-glucan and chitin content [18]. Although we did not observe any morphological change in the filaments of _P. essandensis_, we could still notice that upon carrageenanans treatment, some cells became yellow, a feature commonly observed in laboratory, when the cultures of _P.