Polyamine Putrescine Regulates Oxidative Stress and Autophagy of Hemocytes Induced by Lipopolysaccharides in Pearl Oyster Pinctada fucata martensii

The polyamine putrescine (Put) is a ubiquitous small cationic amine. It plays an essential role in controlling the innate immune response. However, little is known about its function in mollusks. In this study, the Put content was observed to increase in the serum of pearl oyster Pinctada fucata martensii after 6 and 24 h of lipopolysaccharide (LPS) stimulation. Activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) increased, and nitric oxide synthase was downregulated in the Put group (i.e., combined treatment with Put and LPS) compared with that in the LPS group (i.e., combined treatment with phosphate-buffered saline and LPS). Furthermore, activities of alkaline phosphatase and acid phosphatase were inhibited after 6 h of LPS stimulation. The expression levels of the nuclear factor kappa B, IκB kinase, Janus kinase, and signal transducer and activator of transcription proteins genes were all significantly suppressed at 12 and 24 h in the Put group. Pseudomonas aeruginosa and Bacillus subtilis grew better after being incubated with the serum from the Put group than that from the LPS group. Additionally, the Put treatment remarkably inhibited the autophagy of hemocytes mediated by the AMP-activated protein kinase-mammalian target of rapamycin-Beclin-1 pathway. This study demonstrated that Put can effectively inhibit the inflammatory response induced by LPS in pearl oysters. These results provide useful information for further exploration of the immunoregulatory functions of polyamines in bivalves and contribute to the development of immunosuppressive agents.

Comparison in Growth, Feeding, and Metabolism Between a Fast-Growing Selective Strain and a Cultured Population of Pearl Oyster (Pinctada fucata martensii)

Pearl oyster (Pinctada fucata martensii) is the main species cultured for marine pearls in the world. A breeding program was carried out for desirable production traits, including high growth rate, and a fast-growing selective strain of pearl oysters was established. In the current study, we compared the growth characteristics between a selective strain and a cultured population of P. f. martensii in Beihai, Guangxi Province, China. Large size (SL) and small size (SS) individuals of the selective strain were selected, and the differences of physiological and metabolic indexes, such as feeding, respiration, excretion, and enzyme activities between SL and SS and cultured population (CL), were also compared. The results showed that at the age of 6 months, pearl oysters of the selective strain were 14.61% larger than CL, and the proportion of SL (30–40 mm) was 59%, which was two times higher than CL (28%). SL with a rapid growth rate had a high clearance rate (CR), and the CR of SL was about 1.8 times higher than that of CL and 5 times higher than that of SS. In addition, the activities of digestive enzymes (amylase, pepsin, and lipase) and growth-related carbonic anhydrase enzymes in SL were higher than those in the other two groups (p < 0.05). SS with a slow growth rate had higher oxygen consumption (OCR) and ammonia excretion (AER) rates than SL and CL (p < 0.05). Our results suggest that the rapid growth of the selective strain P. f. martensii can be attributed to increased energy intake and reduced energy consumption.