# A Novel Benthic Phage Infecting _Shewanella_ with Strong Replication Ability
## 1 Introduction  
In their natural environment, phages are important agents influencing the physiology and survival of prokaryotes and have significant impacts on the microbially driven biogeochemical cycles [1; 2; 3]. In recent decades, extensive studies on marine phages in seawater have been carried out via field investigation, laboratory isolation, gene-based analysis, and metaproteomic methods. Now we have a certain understanding of the biological characteristics, community composition, and ecological functions of the planktonic phages. The total amount of bacteriophage in the ocean is estimated to be ca. \(10^{30}\), about 15-fold times than prokaryotes [2]. Phage infections significantly control the bacterial mortality and, through viral shunt, affect nutrient cycling and food web dynamics [2; 4]. Recently, the most abundant plankton in the oceans, SAR11 bacteria, formerly considered immune to phage predation, was found also susceptible to dominant phages (i.e., pelagiphages) in seawater [5]. Meanwhile, phage infection can promote the coevolution of bacteria and phages [4]. Many phages have been found to contain host genes via lateral gene transfer and participate in the host metabolism, such as the genes (_psbA_ and _psbD_) encoding for photosynthetically important proteins, which were recently found in a number of cultured cyanophage genomes [6]. By contrast, so far there is still a great lack of knowledge about benthic phages, particularly the benthic phages in coastal sediments. For example, although previous gene-based analysis has revealed that the coastal sediments contain extremely diverse phages and may play important roles in driving carbon cycles [7; 8], benthic phages have been rarely isolated from coastal sediments in the laboratory, which largely limits our understanding of their biological characteristics. At present, isolation and characterization of benthic phages infecting ecologically important bacteria is especially vital for us to explore the mystery of phage activities in coastal sediments. _Shewanella_ is an ecologically important bacterial genus, whose members are widely distributed in freshwater, seawater, sediment, and deep ocean [9]. Members of the genus _Shewanella_ have multiple metabolic capabilities and have potentials in bioremediation and microbial energy generation [10]. Meanwhile, they were considered to be model organisms to study the microbially driven carbon-cycling process [11]. Till now, only nine _Shewanella_ phage genomes have been sequenced, including four siphoviruses (i.e., 1/44, 3/49, Spp001, and SppYZU05) and five mycoviruses (i.e., 1/4, 1/40, 1/41, SFcil, and SppYZU01) [12; 13; 14; 15]. The nine _Shewanella_ phages were isolated from various environments, but none was from marine sediments. Phage SppYZU01 infecting _S.__balica_ and phages SppYZU05, Spp001 infecting _S.__putrefaciens_ were isolated from waste effluents of a seafood market [12; 13]. Phage SFc11 infecting _S.__filelis_ was isolated from the seawater of Mission Bay [14]. The remaining five _Shewanella_ phages were isolated from Baltic Sea ice [15]. As we know, members of _Shewanella_ are widespread in marine sediments [9] and play important roles in extracellular electron transfer [16], reduction of humic acids and iron [10], and degradation of persistent organic compounds, such as petroleum, chlorinated solvents, tiazine, and tetrachloroethene [17]. However, phages infecting _Shewanella_ spp. from marine sediments had never been reported. Even sediment phages are rarely reported. So far, to the best of our knowledge, only two phages isolated from coastal sediments have been comprehensively identified (including the genome annotation), whose hosts are _Vibrio parahaemolyticus_ and _Acinetobacter baumannii_, respectively [18; 19]. In this study, _Shewanella indica_ KJW27, which was isolated from coastal sediments of the Arabian Sea [20], was used as the host bacterium, to isolate its phages from the coastal sediments of Yellow Sea, China.