Distinguishing Activities in the Photodynamic Arsenals of the Pigmented Ciliates Blepharisma sinuosum Sawaya, 1940 and Blepharisma japonicum Suzuki, 1954 (Ciliophora: Heterotrichea)

Biodiversity-safeguarding threshold for urea-fertilizer application on paddy fields: Protozoa-based toxicity tests

Urea is a widely applied fertilizer to enhance crop yields. Ecological risks associated with the excessive application of urea fertilizer threaten the paddy fields' sustainable agriculture and biodiversity preservation. There are no practical thresholds based on proven data on microbial communities. Protozoa are nitrogen-sensitive organisms. For the first time, this study conducted acute and chronic urea toxicity tests on eight species of organisms. The results indicate that Blepharisma sp. is the most sensitive species to urea exposure and is a suitable indicator for determining the safe threshold of urea. This study estimated the predicted no-effect concentration using species sensitivity distribution curves. Subsequently, it established the threshold for urea application in rice fields based on the fields' area and the surface water's height. The short-term safety threshold for urea in the studied paddy field with black soil is 87.7 mg/L, equivalent to 43.85 kg of urea per hectare for a single nitrogen fertilizer application. The long-term safety threshold is 5.02 mg/L, representing the concentration for re-applicating urea. The biodiversity-safeguarding application threshold provides the basis for developing a urea fertilizer reduction protocol to safeguard the paddy fields' biodiversity.

Exploring the impact of urban pollution on ciliate diversity along the Sapucaí River (Minas Gerais, Brazil) via DNA metabarcoding

BACKGROUND

Protists are diverse single-celled eukaryotes found in various habitats. They exhibit a wide range of forms and functions, representing a significant portion of the eukaryotic tree of life, which also includes animals, plants, and fungi. Due to their high sensitivity to environmental changes, these organisms are widely used as biological indicators of organic pollution.

METHODS AND RESULTS

We investigated the molecular diversity of ciliate protists at seven strategic points along the Sapucaí River (Itajubá, Minas Gerais State, Brazil), to assess the impact of urban pollution on the richness, abundance, and diversity indexes of these communities. For each sampling point, values of physicochemical parameters were also recorded. DNA sequences were obtained by high-throughput sequencing (HTS) and analyzed using the V4 18S-rRNA molecular marker, employing the DNA metabarcoding method. We recorded 125 ciliate taxonomic units (OTUs), with nearly 80% corresponding to the classes Spirotrichea, Oligohymenophorea, and Litostomatea. At the genus level, 54 OTUs (43.2%) were identified, spanning 28 genera.

CONCLUSIONS

The composition of ciliates varied significantly along the river's course, from upstream to downstream of Itajubá city. Samples collected from the urban area displayed the lowest richness and diversity, corroborating the influence of the pollution gradient on these communities. The physicochemical parameters showed little variation among the samples and were not linked to the observed changes in ciliate communities, revealing that these organisms are strongly affected by environmental changes and respond more sensitively to these disturbances than physicochemical parameters, emphasizing their potential as bioindicators.

Bioactive Molecules from Ciliates: Structure, Activity, and Applicative Potential

Ciliates are a rich source of molecules synthesized to socialize, compete ecologically, and interact with prey and predators. Their isolation from laboratory cultures is often straightforward, permitting the study of their mechanisms of action and their assessment for applied research. This review focuses on three classes of these bioactive molecules: (i) water‐borne, cysteine‐rich proteins that are used as signaling pheromones in self/nonself recognition phenomena; (ii) cell membrane‐associated lipophilic terpenoids that are used in interspecies competitions for habitat colonization; (iii) cortical granule‐associated molecules of various chemical nature that primarily serve offence/defense functions.

Ciliate Diversity From Aquatic Environments in the Brazilian Atlantic Forest as Revealed by High-Throughput DNA Sequencing

Rainforest aquatic ecosystems include complex habitats with scarce information on their unicellular eukaryote diversity and community structure. We have investigated the diversity of ciliates in freshwater and brackish environments along the Brazilian Atlantic Forest, based on the hypervariable V4 region of the 18S-rDNA obtained by high-throughput DNA sequencing. Our analyses detected 409 ciliate taxonomic units (OTUs), mostly attributed to the classes Oligohymenophorea and Spirotrichea. A total of 11 classes, 12 subclasses, 112 genera, and 144 species were reported. We found the following: (a) the ciliate communities are more diverse in freshwater- than in Atlantic Forest-associated brackish environments; (b) the ciliate communities are composed by a small amount of highly abundant OTUs, but a high number of low-abundant or rare OTUs; (c) nearly one-third of the ciliate OTUs share less than 97% sequence identity to reference sequences and (d) phylogenetic inference supports the hypothesis that the V4 region of the Ciliophora 18S-rDNA is a suitable marker for accurate evolutionary inferences at class level. Our results showed that a considerable fraction of the HTS-detected diversity of ciliates from Brazilian Atlantic Forest is not represented in the currently available molecular databases.