Cyanobacterial and algal abundance and biomass in cave biofilms and relation to environmental and biofilm parameters

Abstract

Due to life in extreme environments, cyanobacteria and algae from cave biofilms that form at the entrances or deep inside the cave around artificial lights are of increasing interest to many scientists. It is well-known that many phototrophic microorganisms are first to colonize exposed substrata and produce the organic matter on which other biofilm constituents relly. Many studies dealing with phototrophic microorganisms from biofilms focus on the diversity and community composition of cyanobacteria and algae, while quantitative assessments are rarely implemented. Biofilm sampling was conducted in Degurić and Vernjikica Cave located in Western and Eastern Serbia, respectively. Ecological parameters (temperature, relative humidity, light intensity) and distance from the entrance were measured. Additionally, chlorophyll content, as well as biofilm parameters (water content, organic and inorganic matter) were determined. The abundance of phototrophic microorganisms was assessed on microscope slides which contained 1 mg of biofilm that was dehydrated for a short period of time and homogenized prior to slide preparation, and then rehydratated. The biomass of recorded cyanobacterial and algal taxa was calculated by applying geometric approximations and standard mathematical formulas. In Degurić Cave, at the sampling site where the highest biomass was documented, the higher diversity, water content and chlorophyll values were also recorded, while in Vernjikica Cave a high content of organic matter was documented. According to the multivariate analyses performed, the biomass of simple trichal Cyanobacteria, Bacillariophyta, and Xanthophyta was positively correlated with the content of organic matter in biofilm and light intensity, while coccoid and heterocytous Cyanobacteria and Chlorophyta

Gloeobacter and the implications of a freshwater origin of Cyanobacteria

“…All known strains of Gloeobacter grow in low-salinity habitats, which was confirmed by the study of compatible solutes in a number of cyanobacteria by Blank (2013a). Mareš et al (2013aMareš et al ( , 2013bMareš et al ( , 2013c showed that Gloeobacter violaceus is a widespread terrestrial organism (see also Chrismas et al 2015;Pushkareva et al 2015;Williams et al 2016;Popovic et al 2019), although it has also been found in shallow freshwater cyanobacterial mats (Lionard et al 2012) A second species, Gloeobacter kīlaueensis J.W. Saw et al, was isolated as the dominant cyanobacterium in a 5 mm thick epilithic biofilm at the entrance to a lava cave in the Kīlauea Caldeira, Hawaiʻi (Saw et al 2013).…”

Does Microbial Diversity of Cave Ecosystems Differ from Outside? The Case of the Azé Show Cave (France)

“…In fact, outside bio lms are several years old and thus mature, in opposition to cave bio lms that are regularly treated by the curators. Moreover, it was reported that wet [4] and illuminated surfaces [20], such as in the outside the Azé cave, are the main factors for Bacillariophyta development.…”

“…Since several decades, the cave microbiome has been studied for several reasons [14] such as medical or pharmaceutical interests (e.g., research of antibio lm compounds) [15] and cave preservation (e.g., Paleolithic drawings and rock paintings curation) [16,17,18]. These studies have been carried out using a large set of microorganism identi cation technics such as microscopic methods [19,20], isolation and culture in laboratory [21], cloning followed by Sanger sequencing [22,23,24], ampli ed ribosomal DNA restriction analysis [25] or high throughput sequencing [6,26,27,28]. Results of these studies have demonstrated that cave microorganisms developing inside bio lms may be involved in speleogenesis processes.…”

Facing Phototrophic Microorganisms That Colonize Artistic Fountains and Other Wet Stone Surfaces: Identification Keys

“…Some of the main features that would be observed are related to the shape of the cells, the presence or absence of the sheaths, the division type, the end cells morphology in the case of the filamentous cyanobacteria, the presence of motility phenomena, the plastids position and their shape in the case of green algae. It is possible to make deeper investigations by evaluating the ratio within the main phototrophic groups, as Popović et al [36] describe a detailed procedure for the mixed phototrophic biofilms.…”