Structure and partial protein profiles of the peritrophic membrane (PM) from the gut of the shrimp Litopenaeus vannamei Liyan Wang, Fuhua Li, Bing Wang, Jianhai Xiang * Institute of Oceanology, Chinese Academy of Sciences, 7 Nanhai Road, Qingdao 266071, PR China article info Article history: Received 31 May 2012 Received in revised form 11 September 2012 Accepted 11 September 2012 Available online 28 September 2012 Keywords: Peritrophic membrane Shrimp Litopenaeus vannamei Immunity abstract Peritrophic membrane (PM) is a non-cellular structure surrounding the food bolus in invertebrate’s midgut. In this study, the shrimp Litopenaeus vannamei was found continuously secreting a tube-like PM enclosing the fecal pellets. The PM structure was membranous in this penaeid shrimp which was similar to that in Sicyonia ingentis studied and was primarily composed of chitin and proteins. Chitin was detected along the whole PM. By using the approach of gel electrophoresis and mass spectrometry of tryptic peptides, the most extracted proteins from the shrimp PMs were identified mainly including digestion-related, immune-related, antioxidant proteins and proteins related to PM structure. This suggests that PM may participate in modulating its permeability and immobilizating the digestive enzymes, actively protect the gut from pathogen contact, and play an important role in the gut immune system. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction In the arthropod digestive tract including foregut, midgut and hindgut, midgut is the only region in contact with the external environment without a cuticle covering. Peritrophic membrane (PM) is a non-cellular membrane lining the arthropod midgut [1], which serves as a barrier between the contents of the gut lumen and the midgut epithelium, protecting the midgut from abrasive food particles and pathogen. PM is considered to be composed of chitin fibrils with associated glycanproteins and proteoglycans [2e 4] and is proposed to assist the digestion process by compart- mentalization of the gut lumen into endoperitrophic space (between the epithelium and the peritrophic membrane) and ectoperitrophic space (between the peritrophic membrane and the lumen) and immobilization of digestive enzymes, allowing for efficient nutrient acquisition and reuse of hydrolytic enzymes. In some cases, it also has functions to inactivate ingested toxin and prevent the oxidation [5e7]. To date, the researches on PM were mostly done in many kinds of insects. The inhibition of insect PM formation was accompanied by increased insect susceptibility to virus infection, then a potential novel strategy for insect pest control was developed by preventing specifically target PM formation [8e10]. However, the researches on Crustacean PMs are very scarce. Shrimp aquaculture is one of the major aquaculture production in the world. Whereas, the outbreak of disease especially caused by white spot syndrome virus (WSSV) has led to high mortality and enormous economic losses. It is extremely urgent to develop novel effective control measures against the outbreak of WSSV. More and more evidences have proved that shrimp gut was one of the primary sites of WSSV replication after an oral infection [11e 13]. Therefore, the significance of PM as an important component of intestinal immune system deserves further research. However, the structure and components of the shrimp PM are still poorly defined. The aims of this study are to compare the structure and basic composition of the PM in Litopenaeus vannamei, the Pacific white shrimp, with that from other species including one other shrimp Sicyonia ingentis and lots of insects, and identify most proteins from its PM. 2. Materials and methods 2.1. Laboratory animal The Pacific white shrimp L. vannamei (>20 g) were raised in seawater aquaria (w1200 L) at 28  C and fed with shrimp food pellets (Haima Incorporation, China) thrice a day. Their water was changed daily. 2.2. Morphology of the PM For scanning electron microscopy (SEM), the shrimp midguts were dissected and cut longitudinally carefully to make the lumen * Corresponding author. Tel.: þ86 532 82898568; fax: þ86 532 82898569. E-mail addresses: jhxiang@ms.qdio.ac.cn, jhxiang@qdio.ac.cn (J. Xiang). Contents lists available at SciVerse ScienceDirect Fish & Shellfish Immunology journal homepage: www.elsevier.com/locate/fsi 1050-4648/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.fsi.2012.09.014 Fish & Shellfish Immunology 33 (2012) 1285e1291