Performance and characterization of snail adhesive mucus as a bioflocculant against toxic Microcystis

Toxic Microcystis blooms are widespread in aquatic bodies, posing major threats to aquatic and human life. Recently, bioflocculants have attracted considerable attention as a promising biomaterial for Microcystis management. In search of a novel organism that can produce an efficient bioflocculant for controlling harmful algae sustainably, the native gastropod Cipangopaludina chinensis was co-cultured continuously with toxic Microcystis under different initial algal cell densities. The bioflocculation effect of snail mucus on toxic Microcystis, microcystin removal, and toxin accumulation in snails was investigated. In addition, the properties of the adhesive mucus were characterized using microscopic, X-ray diffraction, infrared spectroscopy, and polysaccharide and proteome analyses. Microcystis cells were captured and flocculated by the snail mucus; removal efficiencies of up to 89.9% and 84.8% were achieved for microalgae and microcystin-leucine arginine (MC-LR), respectively, when co-cultured with C. chinensis for only one day. After nine-day exposure, less than 5.49 µg/kg DW microcystins accumulated in the snails, indicating safety for human consumption. The snail mucus contained 104.3 µg/mg protein and 72.7 µg/mg carbohydrate, which provide several functional groups beneficial for Microcystis bioflocculation. The main monosaccharide subunits of polysaccharides are galactose, galactosamine, glucosamine, fucose, glucose, and mannose. Most of them are key components of polysaccharides in many bioflocculants. Gene Ontology analysis indicated the protein enrichment in binding processes and catalytic activity, which may account for Microcystis bioflocculation via protein binding or enzymatic reactions. The findings indicate that native C. chinensis secretes adhesive mucus that can act as bioflocculant for toxic Microcystis from ambient water and can be an effective and eco-friendly tool for Microcystis suppression.

Characterization of the shell proteins in two freshwater snails Pomacea canaliculata and Cipangopaludina chinensis

Uncovering the molecular mechanism of shell formation not only reveals the evolution of molluscs but also lay a foundation for shell-inspired biomaterial synthesis. Shell proteins are the key macromolecules of the organic matrices that guide the calcium carbonate deposition during shell mineralization and have thus been intensively studied. However, previous studies on shell biomineralization have mainly focused on marine species. In this study, we compared the microstructure and shell proteins in the apple snail Pomacea canaliculata which is an alien species that has invaded Asia, and a freshwater snail Cipangopaludina chinensis which is native to China. The results showed that although the shell microstructures were similar in these two snails, the shell matrix in C. chinensis contained more polysaccharides. Moreover, the compositions of shell proteins were quite different. While the shared 12 shell proteins (including PcSP6/CcSP9, Calmodulin-A, and proline-rich protein) were supposed to play key roles in shell formation, the differential proteins were mainly immune components. The presence of chitin in both shell matrices and the chitin-binding domains containing PcSP6/CcSP9 underpinned the relevance of chitin as a major fraction in gastropods. Interestingly, carbonic anhydrase was absent in both snail shells, suggesting that freshwater Gastropods might have unique pathways to regulate the calcification process. Our study suggested that shell mineralization might be very different in freshwater and marine molluscs, and therefore, the field should pay more attention to the freshwater species to achieve a more comprehensive insight into biomineralization.

Comparison of gut microbiome in the Chinese mud snail (Cipangopaludina chinensis) and the invasive golden apple snail (Pomacea canaliculata)

Background

Gut microbiota play a critical role in nutrition absorption and environmental adaptation and can affect the biological characteristics of host animals. The invasive golden apple snail (Pomacea canaliculata) and native Chinese mud snail (Cipangopaludina chinensis) are two sympatric freshwater snails with similar ecological niche in southern China. However, gut microbiota comparison of interspecies remains unclear. Comparing the difference of gut microbiota between the invasive snail P. canaliculata and native snail C. chinensis could provide new insight into the invasion mechanism of P.canaliculata at the microbial level.

Methods

Gut samples from 20 golden apple snails and 20 Chinese mud snails from wild freshwater habitats were collected and isolated. The 16S rRNA gene V3-V4 region of the gut microbiota was analyzed using high throughput Illumina sequencing.

Results

The gut microbiota dominantly composed of Proteobacteria, Bacteroidetes, Firmicutes and Epsilonbacteraeota at phylum level in golden apple snail. Only Proteobacteria was the dominant phylum in Chinese mud snail. Alpha diversity analysis (Shannon and Simpson indices) showed there were no significant differences in gut microbial diversity, but relative abundances of the two groups differed significantly (P < 0.05). Beta diversity analysis (Bray Curtis and weighted UniFrac distance) showed marked differences in the gut microbiota structure (P < 0.05). Unique or high abundance microbial taxa were more abundant in the invasive snail compared to the native form. Functional prediction analysis indicated that the relative abundances of functions differed significantly regarding cofactor prosthetic group electron carrier and vitamin biosynthesis, amino acid biosynthesis, and nucleoside and nucleotide biosynthesis (P < 0.05). These results suggest an enhanced potential to adapt to new habitats in the invasive snail.

Comparison of the composition and function of gut microbes between adult and juvenile Cipangopaludina chinensis in the rice snail system

Cipangopaludina chinensis is an important economic value snail species with high medicinal value. The gut microbes of aquatic animals plays a vital role in food digestion and nutrient absorption. Herein, we aimed at high-throughput sequencing of 16S rRNA to further investigate whether there were differences in the composition and function of gut microbes of adult and juvenile C. chinensis snails, as well as sediments. This study found that the microbial diversity of the sediment was significantly higher than that of the snails gut (P < 0.001), but there was no significant difference between the gut flora of adult and juvenile snails (P > 0.05). A total of 47 phyla and 644 genera were identified from all samples. Proteobacteria and Verrucomicrobia were the two dominant phyla in all samples, and overall relative abundances was 48.2% and 14.2%, respectively. Moreover, the relative abundances of Aeromonas and Luteolibacter in the gut of juvenile snails (30.8%, 11.8%) were higher than those of adults (27.7%, 10.6%) at the genus level (P > 0.05). Then, four indicator genera were found, namely Flavobacterium, Silanimonas, Geobacter and Zavarzinella, and they abundance in the gut of juvenile snails was significantly higher than that of adults (P < 0.05). This results imply the potential development of Silanimonas as a bait for juvenile snail openings. We observed that Aeromonas was the primary biomarker of the snail gut and sediments (P < 0.001), and it may be a cellulose-degrading bacteria. Function prediction revealed significantly better biochemical function in the snail gut than sediments (P < 0.001), but no significant differences in adult and juvenile snail (P > 0.05). In conclusion, studies show that the snail gut and sediment microbial composition differ, but the two were very similar. The microbial composition of the snail gut was relatively stable and has similar biological functions. These findings provide valuable information for in-depth understanding of the relationship between snails and environmental microorganisms.

[A comparative study of phenoloxidase activity between Cipangopaludina chinensis and Oncomelania hupensis]

OBJECTIVE

To study the differences of the phenoloxidase (PO) relative activity among ribbed shelled Oncomelania hupensis, smooth shelled O. hupensis and Cipangopaludina chinensis.

METHODS

The crude PO fluid was extracted from the soft tissue of O. hupensis and C. chinensis by homogenation and centrifugation. The PO activity was detected with catechol as the substrate in the reaction systems.

RESULTS

The PO relative activities in the ribbed shelled O. hupensis, smooth shelled O. hupensis and C. chinensis were (25.72 ± 2.27), (14.56 ± 1.24) U / mL and (13.72 ± 1.06) U / mL. The PO relative activity in the smooth shelled O. hupensis was higher than that in the ribbed shelled O. hupensis (q = 21.46, P < 0.05) and C. chinensis (q = 12.00, P < 0.05), while the difference between the PO relative activities of the latter two was not statistically significant (q = 1.62, P > 0.05) .

CONCLUSIONS

There is a difference in the relative PO activity between O. hupensis and C. chinensis, which may be related to the living environment of snails.

Lifelong neurogenesis in the cerebral ganglion of the Chinese mud snail, Cipangopaludina chinensis

INTRODUCTION

A small group of Gastropods possessing giant neurons have long been used to study a wide variety of fundamental neurophysiological phenomena. However, the majority of gastropods do not have large neurons but instead have large numbers of small neurons and remain largely unstudied. We explored neuron size and rate of increase in neuron numbers in the Chinese mud snail, Cipangopaludina chinensis.

METHODS

Using histological sections and whole mounts of the cerebral ganglia, we collected cross-sectional data on neuron number and size across the lifespan of this animal. Neurogenesis was verified using Click-it EdU staining.

RESULTS

We found that total neuron number in the cerebral ganglia increases throughout the lifespan of this species at a constant rate. New neurons arise primarily near the nerve roots. Females live longer (up to 7 years) than males (up to 5 years) and thus achieve larger numbers of neurons in the cerebral ganglion. Neuron size is consistently small (<10 μm) in the cerebral ganglia at all ages, however, cells in the posterior section of the cerebral ganglia are modestly but significantly larger than cells at the anterior.

CONCLUSIONS

These features suggest that C. chinensis and similar species of Caenogastropoda are good candidates for studying gastropod neurogenesis, senescence, and sex differences in the nervous system.