Inducible viral receptor, A possible concept to induce viral protection in primitive immune animals

A pseudolysogen (PL) is derived from the lysogenic Vibrio harveyi (VH) which is infected with the VHS1 (Vibrio harveyi Siphoviridae-like 1) bacteriophage. The lysogenic Vibrio harveyi undergoes an unequivalent division of the extra-chromosomal VHS1 phage genome and its VH host chromosome and produces a true lysogen (TL) and pseudolysogen (PL). The PL is tolerant to super-infection of VHS1, as is of the true lysogen (TL), but the PL does not contain the VHS1 phage genome while the TL does. However, the PL can become susceptible to VHS1 phage infection if the physiological state of the PL is changed. It is postulated that this is due to a phage receptor molecule which can be inducible to an on-and-off regulation influence by an alternating condition of the bacterial host cell. This characteristic of the PL leads to speculate that this phenomenon can also occur in high organisms with low immunity such as shrimp. This article proposes a hypothesis that the viral receptor molecule on the target cell can play a crucial role in which the invertebrate aquaculture animals can become tolerant to viral infection. A possible mechanism may be that the target cell disrupts the viral receptor molecule to prevent super infection. This concept can explain a mechanism for the prevention of viral infection in invertebrate animals which do not have acquired immunity in response to pathogens. It can guide us to develop a mechanism of immunity to viral infection in low-evolved-immune animals. Also, it can be an additional mechanism that exists in high immune organism, as in human for the prevention of viral infectio

Evidence for Phage-induced virulence in the shrimp pathogen

Vibrio species comprise the most frequently encountered bacterial pathogens of cultivated shrimp, and V. harveyi is amongst the most virulent. Most V. harveyi strains are luminescent on agar media and also in infected shrimp that are suffering from luminescent disease or luminous bacteriosis. However, not all isolates of V. harveyi are highly virulent. Some can be injected at high dose (10-7 -10 5 cells per g shrimp body weight) without causing shrimp mortality, while other isolates are lethal at 10 -3 per g shrimp body weight or less. In addition, virulence is often lost upon continuous subculture. Simple differentiation of virulent and avirulent isolates has not been successful, although virulence factors including various enzymes (e.g., proteases and lipases), siderophores and proteinaceous toxins have been identified. Because of this and the genetic diversity of V. harveyi, it has been suggested that virulence is acquired via mobile genetic elements. Indeed, recent work has suggested that 2 quite different bacteriophages, one from the family Myoviridae and the other from the family Siphoviridae, can change the phenotype of V.harveyi isolates from non-virulent to virulent. The host range for both bacteriophages is relatively narrow. A similar phenomenon occurs in V. cholerae, where conversion to virulence is mediated by a filamentous phage (Inovirus) from the family Inoviridae. Altogether, the current information suggests that there may be diverse groups of phages and complementary Vibrio hosts that could mediate virulence in V. harveyi and make the process quite complex. It also suggests that virulence of other Vibrio pathogens of shrimp may be influenced by bacteriophages. Thus, the use of bacteriophages for biological control of pathogenic Vibrio species in aquaculture should include environmental impact studies on the potential for transfer of virulence or antibiotic resistance genes