Abstract
Marinobacter is the abundant and important algal-associated and hydrocarbon biodegradation bacteria in the ocean. However, little knowledge about their phages has been reported. Here, a novel siphovirus, vB_MalS-PS3, infecting Marinobacter algicola DG893(T), was isolated from the surface waters of the western Pacific Ocean. Transmission electron microscopy (TEM) indicated that vB_MalS-PS3 has the morphology of siphoviruses. VB_MalS-PS3 was stable from −20 to 55°C, and with the latent and rise periods of about 80 and 10 min, respectively. The genome sequence of VB_MalS-PS3 contains a linear, double-strand 42,168-bp DNA molecule with a G + C content of 56.23% and 54 putative open reading frames (ORFs). Nineteen conserved domains were predicted by BLASTp in NCBI. We found that vB_MalS-PS3 represent an understudied viral group with only one known isolate. The phylogenetic tree based on the amino acid sequences of whole genomes revealed that vB_MalS-PS3 has a distant evolutionary relationship with other siphoviruses, and can be grouped into a novel viral genus cluster with six uncultured assembled viral genomes from metagenomics, named here as Marinovirus. This study of the Marinobacter phage vB_MalS-PS3 genome enriched the genetic database of marine bacteriophages, in addition, will provide useful information for further research on the interaction between Marinobacter phages and their hosts, and their relationship with algal blooms and hydrocarbon biodegradation in the ocean.
Highlights
The Marinobacter genus is within the class Gammaproteobacteria, order Oceanospirillales and includes Gram-negative, aerobic, motile, halotolerant or halophilic, rod-shaped bacteria (Gauthier et al, 1992), and well known for algal-associated bacteria and its capacity of hydrocarbon degradation, using aromatic and aliphatic hydrocarbons as its sole carbon source (Martin et al, 2003; Holtzapple and Schmidt-Dannert, 2007; Kim et al, 2017)
In order to establish the infection efficacy of each phage, host range tests were evaluated on a range of Marinobacter species by using a cross infectivity test (Table 1). 200 μl of bacteriophage suspension (108 PFU) was mixed with 200 μl of an overnight bacterial culture undergoing exponential growth (OD = 600) and with 4.5 ml of top agar and poured onto the LB agar, SM buffer alone was used as a blank control (Kajsík et al, 2019)
Phytoplankton blooms can cause acute effects on marine ecosystems, one hypothesis is that bacteria producing photoactive iron carriers can provide a bioavailable form of iron for symbiotic phytoplankton, which in turn will affect the growth and bloom dynamics of algae (Yarimizu et al, 2018)
Summary
The Marinobacter genus is within the class Gammaproteobacteria, order Oceanospirillales and includes Gram-negative, aerobic, motile, halotolerant or halophilic, rod-shaped bacteria (Gauthier et al, 1992), and well known for algal-associated bacteria and its capacity of hydrocarbon degradation, using aromatic and aliphatic hydrocarbons as its sole carbon source (Martin et al, 2003; Holtzapple and Schmidt-Dannert, 2007; Kim et al, 2017). Marinobacter squalenivorans and Marinobacter alkaliphilus have the capacity to degrade hydrocarbon compounds (Shieh et al, 2003; Singer et al, 2011) These Marinobacter species have developed complex and diverse metabolic capacities to adapt to polluted and sometimes hypersaline environments. They can degrade hexadecane, fluoranthene, pristine, and octadecane and even metabolize the herbicide 1, 3-diphenylurea (Takai et al, 2005). The degradation products, can play key roles in marine systems, such as promoting the utilization of hydrocarbons and facilitating the absorption of nutrients (Gardner et al, 2004) This genus is potentially involved in complex ecological networks across trophic levels and could be ecologically and evolutionarily influenced by their bacteriophages (Amarillas et al, 2017)
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