Host, pathogen and environment: a bacterial gbpA gene expression study in response to magnesium environment and presence of prawn carapace and commercial chitin

Environmental magnesium ion affects global gene expression, motility, biofilm formation and virulence of Vibrio parahaemolyticus

Vibrio parahaemolyticus is widely distributed in marine ecosystems. Magnesium ion (Mg2+) is the second most abundant metal cation in seawater, and plays important roles in the growth and gene expression of V. parahaemolyticus, but lacks the detailed mechanisms. In this study, the RNA sequencing data demonstrated that a total of 1494 genes was significantly regulated by Mg2+. The majority of the genes associated with lateral flagella, exopolysaccharide, type III secretion system 2, type VI secretion system (T6SS) 1, T6SS2, and thermostable direct hemolysin were downregulated. A total of 18 genes that may be involved in c-di-GMP metabolism and more than 80 genes encoding putative regulators were also significantly and differentially expressed in response to Mg2+, indicating that the adaptation process to Mg2+ stress may be strictly regulated by complex regulatory networks. In addition, Mg2+ promoted the proliferative speed, swimming motility and cell adhesion of V. parahaemolyticus, but inhibited the swarming motility, biofilm formation, and c-di-GMP production. However, Mg2+ had no effect on the production of capsular polysaccharide and cytoxicity against HeLa cells. Therefore, Mg2+ had a comprehensive impact on the physiology and gene expression of V. parahaemolyticus.

Differential transcriptome analysis of the disease tolerant Madagascar-Malaysia crossbred black tiger shrimp, Penaeus monodon hepatopancreas in response to acute hepatopancreatic necrosis disease (AHPND) infection: inference on immune gene response and interaction

Background

Penaeus monodon is the second most widely cultured marine shrimp species in the global shrimp aquaculture industry. However, the growth of P. monodon production has been constantly impaired by disease outbreaks. Recently, there is a lethal bacterial infection, known as acute hepatopancreatic necrosis disease (AHPND) caused by Vibrio parahaemolyticus AHPND strain (Vp_AHPND), which led to mass mortalities in P. monodon. Unfortunately, there is still insufficient knowledge about the underlying immune response of P. monodon upon AHPND infection. The present study aims to provide an insight into the antibacterial immune response elicited by P. monodon hepatopancreas towards AHPND infection.

Methods

We have employed high-throughput RNA-Seq technology to uncover the transcriptome changes of P. monodon hepatopancreas when challenged with Vp_AHPND. The shrimps were challenged with Vp_AHPND through immersion method with dissected hepatopancreas samples for the control group (APm-CTL) and treatment group at 3 (APm-T3), 6 (APm-T6), and 24 (APm-T24) hours post-AHPND infection sent for RNA-Seq. The transcriptome de novo assembly and Unigene expression determination were conducted using Trinity, Tgicl, Bowtie2, and RSEM software. The differentially expressed transcripts were functionally annotated mainly through COG, GO, and KEGG databases.

Results

The sequencing reads generated were filtered to obtain 312.77 Mb clean reads and assembled into 48662 Unigenes. Based on the DEGs pattern identified, it is inferred that the PAMPs carried by Vp_AHPND or associated toxins are capable of activating PRRs, which leads to subsequent pathway activation, transcriptional modification, and antibacterial responses (Phagocytosis, AMPs, proPO system). DAMPs are released in response to cell stress or damage to further activate the sequential immune responses. The comprehensive interactions between Vp_AHPND, chitin, GbpA, mucin, chitinase, and chitin deacetylase were postulated to be involved in bacterial colonization or antibacterial response.

Conclusions

The outcomes of this research correlate the different stages of P. monodon immune response to different time points of AHPND infection. This finding supports the development of biomarkers for the detection of early stages of Vp_AHPND colonization in P. monodon through host immune expression changes. The potential genes to be utilized as biomarkers include but not limited to C-type lectin, HMGB1, IMD, ALF, serine proteinase, and DSCAM.

Electronic supplementary material

The online version of this article (10.1186/s13099-019-0319-4) contains supplementary material, which is available to authorized users.