Hercide Atrazine Alters the Microbiota of the Filametous Green Alga Cladophora sp. Cultured from Thailand

Abstract

The attached green alga Cladophora known to harbor microbiota that play important roles in ecosystem, is one of the most common freshwater filamentous green algae in rivers globally, including those in the northern part of Thailand. These rivers mostly run through agricultural regions where herbicides are heavily used to improve crop quality and quantity. The extensively-used herbicide atrazine persists in soil sediments through transport by surface runoff to rivers. The effect of such herbicide contamination on Cladophora microbiota in Thailand have not been investigated. To acquire this information, 16S rDNA amplicons were used to compare microbiota of Cladophora sp. cultures treated with a spectrum of atrazine concentrations. The results showed that the Cladophora microbiome included at least 106 possible Operational taxonomic units (OTUs) representing twelve bacterial phyla which are Acidobacteria, Actinobacteria, Armatimonadetes, Chloroflexi, Cyanobacteria, Deinococcus-Thermus, Epsilonbacteraeota, Nitrospirae, Patescibacteria, Planctomycetes, Proteobacteria, and WPS-2, representing both core and local algal bacteria. The presence of atrazine was also correlated with changes in richness of bacterial taxa suggesting that these algal epibiotic bacteria were differently affected by atrazine treatments.

Spatial Variation of Cladophora Epiphytes in the Nan River, Thailand

“…Having unique characteristics and a high surface area, Cladophora is known as an ecological engineer that provides habitats for several other organisms, e.g., bacteria, archaea, protists, microalgae, fungi, and invertebrates, promoting complex epiphytic communities [6][7][8][9][10]. Previous studies found that these heterogeneous assemblages of living organisms displayed various ecological interactions, e.g., [4,6,7,[9][10][11]. Predation in the algal microbiome could be inferred from the presence of organisms belonging to different trophic levels in the food chain, e.g., producers, herbivores, carnivores, and omnivores, representing organisms of diverse supergroups, e.g., Viridiplantae, Euglenozoa, Stramenopiles, Alveolata, Rhizaria, Amoebozoa, and Eumetazoa [12].…”

“…Predation in the algal microbiome could be inferred from the presence of organisms belonging to different trophic levels in the food chain, e.g., producers, herbivores, carnivores, and omnivores, representing organisms of diverse supergroups, e.g., Viridiplantae, Euglenozoa, Stramenopiles, Alveolata, Rhizaria, Amoebozoa, and Eumetazoa [12]. Competition could be inferred from the alternations or shifts of taxonomic richness and abundance in comparative studies e.g., [11]. For example, dynamic changes in bacterial populations were observed during the algal growth season [6] or when Cladophora grew in media supplemented with different chemical compositions [11], as it happens spontaneously also in the wild plant populations of terrestrial environments, where the same taxon to a different chemical soil composition may produce a different chemotype [13].…”

“…Competition could be inferred from the alternations or shifts of taxonomic richness and abundance in comparative studies e.g., [11]. For example, dynamic changes in bacterial populations were observed during the algal growth season [6] or when Cladophora grew in media supplemented with different chemical compositions [11], as it happens spontaneously also in the wild plant populations of terrestrial environments, where the same taxon to a different chemical soil composition may produce a different chemotype [13].…”

“…Among these ecological interactions, mutualism in the Cladophora microbiomes has been the most well studied, e.g., [4,6,7,[9][10][11]. The mutualistic relationship was inferred from the presence of taxonomic markers and protein-coding genes in metagenomic analyses.…”

“…Studies suggested that the photoautotrophs, i.e., the host Cladophora and epiphytic diatoms, provide habitats and exopolysaccharides that serve as resources for other heterotrophic bacteria and fungi. In return, the heterotrophic bacteria and fungi supply the phycosphere with vitamin B 12 , inorganic minerals, and gases needed for the growth of Cladophora and other microbes in the association [4,6,[9][10][11].…”