**1. Introduction**

Gram-negative bacteria attract attention because of its extraordinary adaptability to natural environment as well as to anthropogenic, including nosocomial conditions. Marine bacteria studied since 1960s were found to be the most psychro-, piezo-, and halo-tolerant [1]. Moreover marine bacteria inhabit in oligotrophic environment with deficiency or lack of sunlight. Investigation of these bacteria revealed pressure regulation of the proteins expression [2], multiplication of genes important for metabolic pathways, and cell motility and other molecular mechanisms of the adaptation to extreme conditions [3].

Detection of the many carbon and energy utilization pathways in marine bacteria prompted the researchers to study on the properties of these bacteria as a tool for degradation of environmental pollution. Every year more attention is paid to this problem. Oil and petroleum products are the most common pollutants that disrupt and inhibit all life processes. These products accumulate as difficult-oxidized forms of substances that change the direction of metabolism and the natural ratio of the number of microorganisms in ecosystems. This leads to a slowdown in the process of microbial purification of ocean waters.

One of the most promising areas for investigating this problem is the Arctic Ocean, the smallest of the oceans which is almost completely surrounded by earth. For this reason, it has the most extensive shelf areas in comparison with any ocean basin and a significant proportion of terrigenous organic carbon flowing through rivers into the Arctic Ocean [4]. In order to determine the diversity of bacteria involved in bacterial consortia that are capable of degrading hydrocarbons, some studies were conducted in the Chukchi Plateau region [5]. Authors showed that a number of species are involved in this process. So, the potential degraders including *Cycloclasticus, Pseudomonas*, *Halomonas*, *Pseudoalteromonas*, *Marinomonas*, *Bacillus*, *Colwellia*, *Acinetobacter*, *Alcanivorax*, *Salinisphaera,* and *Shewanella*, with *Dietzia* as the most abundant, occurred in all sediment samples.

Marine sediment and water samples are the source for peptide-based drug discovery. Non-ribosomal peptides from Proteobacteria have recently attracted much attention as a source of new drugs [6]. Currently, there is considerable research interest in determining the chemical features of major components of cell envelope of marine bacteria, first of all, lipopolysaccharide (LPS) [7]. Lipid A, which is a structural component of the LPS of some marine bacteria, is considered an antagonist to endotoxins of gram-negative bacteria [8].

This is due to the fact that, in comparison with terrestrial bacteria, biologically active compounds of which are successfully used in the pharmaceutical industry, the biological potential of marine bacteria in this regard has not been practically realized [9].

However, the penetration process of the marine bacteria cells is the most intriguing. Gram-negative bacteria are covered by two distinct biological membranes. A well-established response of poikilothermic organisms to low temperature and high pressure exposure is a change in membrane fluidity [10]. There are two major classes of membrane transport proteins: transporters and channels, which are influenced by this change. Outer membrane (OM) channels include porin superfamily. These outer membrane channels share a beta-barrel structure that differ in strand and shear number. Porin superfamily comprises classical (gram-negative) porins, maltoporin-like channels, and ligand-gated protein channels cooperating with a TonB-associated inner membrane complex [11].

Classical (gram-negative) porins are known as OmpF, OmpC, and PhoE in *Escherichia coli.* To date, significant progress has been achieved in the study of the structure and function of porins of the terrestrial gram-negative bacteria, mainly members of the family Enterobacteriaceae [12,13]. However, classical porins are of the greatest interest in the context of the mechanism that mediates uptake of small molecules, including antibiotics [13].

OM porins of marine bacteria play an important role in the adaptation to the extreme environment. Few studies shed light on the role and functioning of porins of aquatic bacteria, including marine bacteria. The consequence of structural changes in the porins may be reduced permeability of the bacterial membrane for solutes. For example, in aquatic inhabitant of *Pseudomonas aeruginosa*, the permeability of the outer membrane is lower in comparison of *E. coli* [14]. Porins of some marine bacteria are sensitive to osmoregulation such as *Vibrio parahaemolyticus* and *V. alginolyticus* [15,16]. In this regard, the porins of marine bacteria are an interesting object of study of the adaptability of microorganisms.

The present study is a continuation of a series of our investigations that are dedicated to the isolation and characterization of functional activities of porins from the OM of marine microorganisms [17,18]. In this study, namely, we have isolated and characterized functional activity and spatial structure of porin from OM of *Marinomonas primoryensis* KMM 3633T. Our interest in this species is due to the fact that the genus *Marinomonas* includes gram-negative bacterial strains common in various marine environments. [19]. In addition, the most recognized species of the genus were isolated from sea water

samples collected from different geographical locations [20]. Some of them were isolated from cold media, such as the sub Antarctic regions, for example *Marinomonas polaris* [21] and *M. ushuaiensis* [22].

During the study of microbial communities associated with marine environments in the Sea of Japan, two bacterial strains were isolated from a coastal sea-ice sample, obtained from a sea-ice column at a depth of 0.8 m in Amursky Bay near Vladivostok, Russia, in March 2001 [23]. The isolates were aerobic, gram-negative, heterotrophic microorganisms with a respiratory metabolism, and had phenotypic characteristics similar to those of the genus *Marinomonas*. They were classified as *Marinomonas primoryensis* sp. nov. [23]. *M. primoryensis* KMM 3633T (= CIP 108051 = IAM 15010) is the type strain of the species. This strain was used in the present study for further investigation.
