Cloning, expression and identification of two glutathione S-transferase isoenzymes from Perna viridis

Microbiota characterization of the green mussel Perna viridis at the tissue scale and its relationship with the environment

Research on the microbiota associated with marine invertebrates is important for understanding host physiology and the relationship between the host and the environment. In this study, the microbiota of the green mussel Perna viridis was characterized at the tissue scale using 16S rRNA gene high-throughput sequencing and compared with the microbiota of the surrounding environment. Different mussel tissues were sampled, along with two environmental samples (the mussel's attachment substratum and seawater). The results showed that the phyla Proteobacteria, Bacteroidetes, and Spirochaetae were dominant in mussel tissues. The bacterial community composition at the family level varied among the tissues of P. viridis. Although the microbiota of P. viridis clearly differed from that of the surrounding seawater, the composition and diversity of the microbial community of the foot and outer shell surface were similar to those of the substratum, indicating their close relationship with the substratum. KEGG prediction analysis indicated that the bacteria harbored by P. viridis were enriched in the degradation of aromatic compounds, osmoregulation, and carbohydrate oxidation and fermentation, processes that may be important in P. viridis physiology. Our study provides new insights into the tissue-scale characteristics of mussel microbiomes and the intricate connection between mussels and their environment.

Bioaccumulation and function analysis of glutathione S-transferase isoforms in Manila clam Ruditapes philippinarum exposed to different kinds of PAHs

This study analyzed the function of different glutathione S-transferase (GST) isoforms and detoxification metabolism responses in Manila clam, Ruditapes philippinarum, exposed to 4 kinds of polycyclic aromatic hydrocarbons (PAHs) single, and their mixtures for 15 days under laboratory conditions. 13 kinds of GSTs in R. philippinarum were classified, and the results of tissue distribution indicated that 12 kinds of GSTs (except GST sigma 3) expressed most in digestive glands. We detected the mRNA expression levels of aryl hydrocarbon receptor signaling pathway, and detoxification system in digestive glands of clams exposed to benzo[a]pyrene (BaP), chrysene (CHR), benzo[a]anthracene (BaA), benzo[b]fluoranthene (BbF), and BaP + CHR + BaA + BbF, respectively. Among these genes, we selected GST-sigma, GST-omega and GST-pi as potential indicators to BaP; GST-sigma, GST-A and GST-rho to CHR; GST-pi, GST-sigma, GST-A, GST-rho and GST-microsomal to BaA; GST-theta and GST-mu to BbF; while GST-pi and GST-mu to the mixture of BaP, CHR, BaA and BbF. Additionally, the bioaccumulation of PAHs in tissues increased remarkably over time, and showed an obvious dose-effect. Under the same concentration, the bioaccumulation in single exposure group was higher than that in mixture group, and the bioaccumulation of PAHs in tissues with different concentrations of stress was irregular. The results revealed the metabolic differences and bioaccumulation rules in clams exposed to four kinds of PAHs, and provided more valuable information for the PAHs risk assessment.

Transcriptomics reveal triphenyltin-induced molecular toxicity in the marine mussel Perna viridis

Triphenyltin (TPT) is widely used as an active ingredient in antifouling paints and fungicides, and continuous release of this highly toxic endocrine disruptor has caused serious pollution to coastal marine ecosystems and organisms worldwide. Using bioassays and transcriptome sequencing, this study comprehensively investigated the molecular toxicity of TPT chloride (TPTCl) to the marine mussel Perna viridis which is a commercially important species and a common biomonitor for marine pollution in Southeast Asia. Our results indicated that TPTCl was highly toxic to adult P. viridis, with a 96-h LC₁₀ and a 96-h EC₁₀ at 18.7 μg/L and 2.7 μg/L, respectively. A 21-day chronic exposure to 2.7 μg/L TPTCl revealed a strong bioaccumulation of TPT in gills (up to 36.48 μg/g dry weight) and hepatopancreas (71.19 μg/g dry weight) of P. viridis. Transcriptome analysis indicated a time course dependent gene expression pattern in both gills and hepatopancreas. Higher numbers of differentially expressed genes were detected at Day 21 (gills: 1686 genes; hepatopancreas: 1450 genes) and at Day 28 (gills: 628 genes; hepatopancreas: 238 genes) when compared with that at Day 7 (gills: 104 genes, hepatopancreas: 112 genes). Exposure to TPT strongly impaired the endocrine system through targeting on nuclear receptors and putative steroid metabolic genes. Moreover, TPT widely disrupted cellular functions, including lipid metabolism, xenobiotic detoxification, immune response and endoplasmic-reticulum-associated degradation expression, which might have caused the bioaccumulation of TPT in the tissues and aggregation of peptides and proteins in cells that further activated the apoptosis process in P. viridis. Overall, this study has advanced our understanding on both ecotoxicity and molecular toxic mechanisms of TPT to marine mussels, and contributed empirical toxicity data for risk assessment and management of TPT contamination.

Cloning, characterization and expression analysis of glutathione S-transferase from the Antarctic yeast Rhodotorula mucilaginosa AN5

The gene for glutathione S-transferase (GST) in Antarctic sea-ice yeast Rhodotorula mucilaginosa AN5 was cloned and expressed in Escherichia coli and named RmGST. Sequence analysis showed that the RmGST gene contained a 843 bp open reading frame, which encoded 280 amino acid residues with a calculated molecular mass of 30.4 kDa and isoelectric point of 5.40. RmGST has the typical C- and N-terminal double domains of glutathione S-transferase. Recombinant RmGST (rRmGST) was expressed in E. coli to produce heterologous protein that had a high specific activity of 60.2 U/mg after purification. The apparent K_m values of rRmGST for glutathione and 1-chloro-2,4-dinitrobenzene were 0.35 mM and 0.40 mM, respectively. Optimum enzyme activity was measured at 35 °C and at pH 7.0 and complete inactivation was observed after incubation at 55 °C for 60 min rRmGST tolerated high salt concentrations (1.0 M NaCl) and was stable at pH 3.0. Additionally, the recombinant protein nearly kept whole activity in Hg²⁺ and Mn²⁺, and could tolerate Ca²⁺, Cu²⁺, Mg²⁺, Cd²⁺, EDTA, thiourea, urea, Tween-80, H₂O₂ and Triton X-100. Real-time quantitative PCR showed that relative expression of the GST gene was significantly increased under Cu²⁺ and low temperature stress. These results indicate that rRmGST is a typical low thermostable enzyme, while its other characteristics, heavy metal and low temperature tolerance, might be related to its Antarctic home environment.

Expression profiles of different glutathione S-transferase isoforms in scallop Chlamys farreri exposed to benzo[a]pyrene and chrysene in combination and alone

Aquatic organisms are increasingly exposed to polycyclic aromatic hydrocarbons (PAHs) due to anthropogenic pressure. This study aimed at evaluating the response of Glutathione S-transferases (GSTs) in scallop Chlamys farreri against benzo[a]pyrene (BaP) and chrysene (CHR) exposure under laboratory conditions. Nine published GST genes were classified into six subfamilies and a new member of rho family was identified for the first time. Twelve GSTs (including nine published GST genes and three in transcriptome established by our laboratory) mRNA transcript levels in the gills, digestive glands, adductor muscle, mantle, testis, ovaries, blood cells of scallops were measured by real-time PCR. The results showed that the mRNA transcript levels of twelve GSTs, except GST-zeta, GST-mu and GST-microsomal, were highest in digestive gland. Accordingly, the mRNA expression levels of GSTs were measured in digestive glands of scallops exposed to BaP (0.1μg/L and 1μg/L), CHR (0.1μg/L and 1μg/L) and their mixtures (0.1μg/L BaP +0.1μg/L CHR and 1μg/L BaP +1μg/L CHR). The results indicated that different GST had specific response to different pollution exposure. In BaP exposure experiment, the mRNA expression level of GST-theta was a potential suitable biomarker. GST-sigma-2 and GST-3, which belonged to sigma class, were sensitive to CHR exposure while GST-microsomal was considered a potential ideal bioindicator to joint exposure of BaP and CHR. In summary, this study investigated the classification of GSTs and provided information about the expression profiles of different class GSTs after PAHs exposure.

De novo transcriptome analysis of Perna viridis highlights tissue-specific patterns for environmental studies

BACKGROUND

The tropical green-lipped mussel Perna viridis is a common biomonitor throughout the Indo-Pacific region that is used for environmental monitoring and ecotoxicological investigations. However, there is limited molecular data available regarding this species. We sought to establish a global transcriptome database from the tissues of adductor muscle, gills and the hepatopancreas of P. viridis in an effort to advance our understanding of the molecular aspects involved during specific toxicity responses in this sentinel species.

RESULTS

Illumina sequencing results yielded 544,272,542 high-quality filtered reads. After de novo assembly using Trinity, 233,257 contigs were generated with an average length of 1,264 bp and an N50 length of 2,868 bp; 192,879 assembled transcripts and 150,111 assembled unigenes were obtained after clustering. A total of 93,668 assembled transcripts (66,692 assembled genes) with putative functions for protein domains were predicted based on InterProScan analysis. Based on similarity searches, 44,713 assembled transcripts and 25,319 assembled unigenes were annotated with at least one BLAST hit. A total of 21,262 assembled transcripts (11,947 assembled genes) were annotated with at least one well-defined Gene Ontology (GO) and 5,131 assembled transcripts (3,181 assembled unigenes) were assigned to 329 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. The quantity of assembled unigenes and transcripts obtained from male and female mussels were similar but varied among the three studied tissues, with the highest numbers recorded in the gills, followed by the hepatopancreas, and then the adductor muscle. Multivariate analyses revealed strong tissue-specific patterns among the three different tissues, but not between sexes in terms of expression profiles for annotated genes in various GO terms, and genes associated with stress responses and degradation of xenobiotics. The expression profiles of certain selected genes in each tissue type were further validated using real-time quantitative polymerase chain reaction assays and a similar tissue-specific trend was seen.

CONCLUSIONS

The extensive sequence data generated from this study will provide a valuable molecular resource for facilitating environmental studies with P. viridis, and highlight the importance of tissue-specific approaches in the future.