Paulina Nowicka-Krawczyk

Algal biofilms contribute to the biodeterioration of building materials (BMs), while restrictions on conventional algicides stimulate the search for sustainable protection strategies. This study evaluated the antialgal potential of selected essential oils and active compounds, with particular emphasis on lemongrass essential oil (LGC), for the control of microalgal biofilms on brick and render surfaces. Three essential oils (Lavandula angustifolia, Melaleuca alternifolia, and Cymbopogon citratus) and two active compounds, eugenol (EU) and geraniol, were screened against terrestrial microalgal strains associated with biodeterioration. Antialgal activity was assessed based on minimum inhibitory and algicidal concentrations. LGC and EU inhibited microalgal growth, reducing photosynthetic activity, chlorophyll a content, and inducing cellular alterations. Metabolomic analysis revealed a strong stress response involving membrane lipid remodeling, oxidative stress, and disruption of photosynthetic metabolism. LGC and EU caused cellular damage, with LGC inducing faster degradation and EU enabling partial adaptation. LGC effectively reduced microalgal biofilms on brick and render, decreased photosynthetic activity, and partially restored surface coloration, without causing significant changes in substrate pH or water absorptivity. Effectiveness depended on biofilm maturity and substrate characteristics. The integrated microbiological, physiological, metabolomic, and material-based approach confirmed the potential of LGC as a sustainable component of future protective coatings for mineral BMs.

Biodeterioration of building materials by aerophytic green algae is increasingly recognized as a significant factor affecting the aesthetic value and durability of brick and plaster façades, yet the biochemical mechanisms underlying this process remain poorly understood. This study investigates the metabolomic profiles of five algal taxa: Chloroidium saccharophilum PNK010, Klebsormidium nitens PNK013, Bracteacoccus minor PNK015, Diplosphaera chodatii PNK021, and Stichococcus bacillaris PNK040 growing on brick and plaster for a year under laboratory and environmental conditions. Untargeted UHPLC–MS/MS metabolomics, with metabolic pathway and chemical-class enrichment analyses, were used to characterize substrate- and condition-associated metabolic signatures and to detect metabolites potentially involved in material deterioration. The research demonstrated strain-specific and substrate-driven metabolic differentiation. Plaster exhibited higher metabolic heterogeneity and stress-related pathways, whereas brick showed more conserved, growth-associated metabolic profiles. Across taxa, low-molecular-weight organic acids, including citric/isocitric, acetic, and oxalic, were recurrently detected, suggesting their potential involvement in acidification- and metal-complexation-related processes at the algal–mineral interface. Enrichment of flavin nucleotides, carboxylic acids, fatty acyls, and aromatic secondary metabolites further supports the involvement of redox activity, stress adaptation, and biofilm persistence. These findings allow a provisional ranking of the algae based on their potential for geochemical biodeterioration, as follows: PNK010 > PNK040> PNK015 > PNK021> PNK013.

The research examined the growth of non-axenic microalgal cultures in liquid digestate for the removal of nutrients and organic contaminants. Five environmental isolates (Chlorella sorokiniana, Tetradesmus obliquus, Desmodesmus subspicatus, Chloroidium saccharophilum, Desmodesmus communis) were cultivated for a period of 120 days comprising two operational phases: Phase 1 without pH control and Phase 2 with pH adjustment. In Phase 1, the microalgal-bacterial cultures achieved up to 69.7 ± 5.1% of total nitrogen (TN) reduction rate, while orthophosphate (PO₄³⁻) removal reached only 46.5 ± 3.8%. In contrast, the pH adjustment in Phase 2 had a dramatic effect on the microalgae growth and treatment efficiency: the TN and orthophosphate removal rates were significantly higher, whereas sCOD reduction lowered. Among the tested non‑axenic cultures, the trials inoculated with Desmodesmus communis achieved the highest overall TN removal rates in both phases (69.7 ± 5.1% in Phase 1 and 89.4 ± 0.8% in Phase 2), whereas PO₄³⁻ reduction was relatively low in Phase 1 but reached 93.8 ± 0.3% in Phase 2. By contrast, cultures inoculated with Tetradesmus obliquus and Chlorella sorokiniana consistently exhibited the lowest TN reduction rates (55.4 ± 1.7–57.9 ± 5.8% in Phase 1 and 85.2 ± 1.6–85.8 ± 1.0% in Phase 2). By comparison, Desmodesmus subspicatus generally performed best in terms of sCOD reduction (69.0 ± 1.9–75.2 ± 0.7%). The pH adjustment significantly increased the density of microalgal coenobia and chlorophyll a concentration and also led to considerable changes in the relative abundance of bacteria. In Phase 1 three bacterial phyla dominated the non‑axenic cultures: Proteobacteria (40.9–75.0%), Bacteroidota (11.5–19.3%) and Actinobacteriota (2.9–27.1%). In Phase 2, NaOH‑driven pH increase clearly restructured the bacterial community: Proteobacteria remained dominant (59.0–78.4%), Bacteroidota declined markedly (1.5–9.0%), and Firmicutes became the second most abundant phylum (2.1–30.4%), while Actinobacteriota were strongly reduced. Overall, the removal of nutrients and organic pollutants was not solely attributable to microalgal activity but likely resulted from complex interactions within the microalgal–bacterial consortia under the contrasting pH regimes of Phases 1 and 2.

This article presents the concept of using a functionalised siloxane compound HOL9 with amphiphilic properties as a coating for cement composites to enhance their antifouling properties against algae. The biological properties of the compound were assessed based on its ability to inhibit chlorophyll fluorescence intensity, which is used as an indicator of photosynthetic activity and biofilm development. The greatest decrease in algal photosynthetic activity was observed for a 10% aqueous solution of HOL9 applied by painting. In these conditions, the maximum ^chlFI value decreased by 97.6%. In addition, the impact of the protective coating containing HOL9 on the fundamental physical and mechanical characteristics of the cement composite, along with its resilience to frost cycling, was thoroughly investigated. The coating applied by immersion demonstrated a 50.7% strength loss after 150 freeze–thaw cycles, while the coating applied by painting exhibited a 43.8% loss. In comparison, the control samples experienced a 42.8% strength reduction. It has been demonstrated that the method of application, the modifier concentration, and the type of solvent can have a substantial impact on the protective properties of concrete. The most marked inhibition of algae photosynthetic activity was observed with a 10% aqueous solution applied by painting.

Aerial green algae colonising building materials in temperate climates form complex biofilms that contribute to the deterioration of man-made structures, reducing their aesthetic value. The present study seeks to address whether algae, already at an early stage of colonisation, can adversely influence building substrates, contributing to biodeterioration beyond mere aesthetic impact. Early-stage colonisers – Chloroidium saccharophilum , Klebsormidium nitens , Bracteacoccus minor , Diplosphaera chodatii , and Stichococcus bacillaris , were isolated from brick and plaster walls, identified using traditional and molecular methods, and grown on experimental brick and plaster substrates. Over six months, algal growth in laboratory and environmental conditions was visualised and monitored by measuring chlorophyll a concentration, fluorescence intensity, and substrate profile height. All taxa were able to grow on both types of substrates at their surface and in the interior part. Most of them formed compact biofilms that filled substrate pores and overgrew the cavities, with some producing membrane-like layers ( K. nitens and S. bacillaris ). Algae with thick cell walls ( C. saccharophilum , D. chodatii , S. bacillaris ) and filamentous K. nitens detached the mineral grains from the brick surface during biofilm separation, as a consequence of prolonged colonisation over time. Except for B. minor , all taxa contributed to the geophysical biodeterioration of brick.

The prevention of biofilm formation and algal biodeterioration on building materials, particularly on cultural heritage sites, is a growing concern. Due to regulatory restrictions on conventional algicidal biocides in Europe, natural alternatives such as essential oils are gaining interest for their potential use in heritage conservation. This study evaluates the anti-algal activity of Salvia officinalis and Equisetum arvense (essential oils, hydrolates, and extracts) against a mixed culture of five green algae species (Bracteacoccus minor, Stichococcus bacillaris, Klebsormidium nitens, Chloroidium saccharophilum, and Diplosphaera chodatii). The plant materials were processed using hydrodistillation and solvent extraction, followed by chemical characterization through gas chromatography–mass spectrometry (GC-MS). Biological efficacy was assessed by measuring algal growth inhibition, changes in biomass colour, chlorophyll a concentration, and fluorescence. S. officinalis yielded higher extract quantities (extraction yield: 23%) than E. arvense and contained bioactive compounds such as thujone, camphor, and cineole, which correlated with its strong anti-algal effects. The essential oil of S. officinalis demonstrated the highest efficacy, significantly inhibiting biofilm formation (zones of inhibition: 15–94 mm) and photosynthetic activity at 0.5% concentration (reduction in chlorophyll a concentration 90–100%), without causing visible discolouration of treated surfaces (∆E < 2). These findings highlight the potential of S. officinalis essential oil as a natural, effective, and material-safe algicidal biocide for the sustainable protection of cultural heritage sites.

This study investigated the treatment of unsterilized, undiluted, and unfiltered liquid digestate in a large-scale photobioreactor over a period of 33 weeks using a consortium of microalgae and bacteria. The generated biomass was analyzed for a wide spectrum of value-added compounds. The impact of organic loading rates (OLR) on the microbial culture was determined, and the influence of the biomass storage method on its qualitative composition was also analyzed. The experiment showed optimal growth of microalgae at OLR = 0.1 gCOD/L/day (where COD is Chemical Oxygen Demand), while a higher OLR value led to culture destabilization. Microglena sp., an algae not commonly applied for digestate treatment, showed low tolerance to changes in process conditions (OLR increase) but high readaptation potential when the OLR was lowered to its initial value. Significant changes in the microbial community were observed during the treatment. In Phases 1 and 2, Desmodesmus subspicatus and Actinomycetota phylum dominated in the community, while in Phase 3, Microglena sp. and Firmicutes were the most abundant. Total nitrogen, orthophosphates, and soluble COD were reduced by 89–99%. The biomass storage method had a notable impact on the content of lipids, fatty acids, and pigments. The protein amount was 32.75–33.59% of total solids (TS), while total lipid content was 15.76–19.00% TS, with stearic and palmitic acid being dominant. The effect of the storage regime on the potential biomass valorization was also discussed.

This study tested the effectiveness of a bifunctional polysiloxane (L43) as a means of protecting concrete surfaces from biocorrosion. L43 was designed to contain two types of functional groups in its structure: surface-active hydrophobic chains and hydrophilic groups that allow the coating to permanently bond to the concrete. L43-coated cement samples achieved compressive strengths exceeding 70 MPa, while samples subjected to cyclic freeze–thaw tests achieved compressive strengths exceeding 33 MPa. In addition, compound L43 at a concentration of 5% reduced the photosynthetic activity of microalgae cells on the concrete surface. The maximum value of chlFI decreased by 69.5%, while the average value decreased by 71.4%. Thus, it was proven that compound L43 effectively counteracts biological corrosion without deteriorating the structure of the impregnated substrate. It should be emphasized that the biocidal effect is due to the structure of the siloxane compound and appropriately selected functional groups. There is no need to add harmful biocides, making the solution environmentally friendly. In addition, the coating allows for free air circulation, which is crucial for the protection of building and construction materials.

Most studies of terrestrial bryophytes as natural substrates for photosynthetic microorganisms have been performed in the polar regions, where bryophytes are an important part of the ecosystem. As they remain green throughout the year, bryophytes may also be an ideal substrate for epiphytic organisms in temperate regions. The present study investigated the colonization potential and diversity of microalgae on selected plant species in riparian forest and spruce monoculture in a temperate region. It examines whether the presence of algae is related to substrate humidity, the micromorphology of gametophyte or the seasonal availability of substrate. The taxonomic diversity of algae was studied. Cyanobacteria and green algae were cultured on BG-11 agar medium, while diatoms were identified in permanent diatomaceous slides. The alpha- and beta-diversity indices were calculated, and the communities were compared using Bray-Curtis distances and multidimensional correspondence analyses. Our findings indicate that the largest number of alga species were diatoms; however, their presence was only observed in riparian forest and was associated with high humidity. Both aerophilic and freshwater taxa were noted, the latter carried by water from nearby aquatic ecosystem. Green algae were present in both phytocoenoses and humidity appears to have no substantial effect on the degree of colonization; their diversity was low and the group consisted of terrestrial taxa. In two bryophytes growing at the highest humidity, cyanobacteria were only identified in culture. The key factor influencing the degree of microalgae colonization was the humidity of the substrate, which was related to the distance from water.