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Background: Isolation of marine microorganisms is fundamental to gather information about their physiology, ecology and genomic content. To date, most of the bacterial isolation efforts have focused on the photic ocean leaving the deep ocean less explored. We have created a marine culture collection of heterotrophic bacteria (MARINHET) using a standard marine medium comprising a total of 1561 bacterial strains, and covering a variety of oceanographic regions from different seasons and years, from 2009 to 2015. Specifically, our marine collection contains isolates from both photic (817) and aphotic layers (744), including the mesopelagic (362) and the bathypelagic (382), from the North Western Mediterranean Sea, the North and South Atlantic Ocean, the Indian, the Pacific, and the Arctic Oceans. We described the taxonomy, the phylogenetic diversity and the biogeography of a fraction of the marine culturable microorganisms to enhance our knowledge about which heterotrophic marine isolates are recurrently retrieved across oceans and along different depths. Results: The partial sequencing of the 16S rRNA gene of all isolates revealed that they mainly affiliate with the classes Alphaproteobacteria (35.9%), Gammaproteobacteria (38.6%), and phylum Bacteroidetes (16.5%). In addition, Alteromonas and Erythrobacter genera were found the most common heterotrophic bacteria in the ocean growing in solid agar medium. When comparing all photic, mesopelagic, and bathypelagic isolates sequences retrieved from different stations, 37% of them were 100% identical. This percentage increased up to 59% when mesopelagic and bathypelagic strains were grouped as the aphotic dataset and compared to the photic dataset of isolates, indicating the ubiquity of some bacterial isolates along different ocean depths. Finally, we isolated three strains that represent a new species, and the genome comparison and phenotypic characterization of two of these strains (ISS653 and ISS1889) concluded that they belong to a new species within the genus Mesonia. Conclusions: Overall, this study highlights the relevance of culture-dependent studies, with focus on marine isolated bacteria from different oceanographic regions and depths, to provide a more comprehensive view of the culturable marine bacteria as part of the total marine microbial diversity.

Strains 2SM5 T and 2SM6, two strictly aerobic chemo-organotrophic gammaproteobacteria, were isolated from Mediterranean seawater off the coast of Vinaroz, Castelló n, Spain, in February, 1990. They were extensively characterized by a polyphasic study that placed them in the genus Pseudomonas. Phylogenetic analysis of 16S rRNA gene sequences showed that both strains shared 100 % sequence similarity and were closely related to members of the Pseudomonas pertucinogena clade, with less than 97.3 % similarity to strains of established species; Pseudomonas xiamenensis was the closest relative. Analysis of sequences of three housekeeping genes, rpoB, rpoD and gyrB, further confirmed the phylogenetic assignment of the Mediterranean isolates. Chemotaxonomic traits such as quinone and polar lipid composition also corroborated the placement of strains 2SM5 T and 2SM6 in the gammaproteobacteria. Other phenotypic traits, including fatty acid composition, enabled clear differentiation of both isolates from other species of Pseudomonas. We therefore conclude that strains 2SM5 T and 2SM6 represent a novel species of Pseudomonas, for which the name Pseudomonas litoralis is proposed; the type strain is 2SM5 T (5CECT 7670 T 5KCTC 23093 T ).The genus Pseudomonas Migula 1894 was described originally to include Gram-negative, strictly aerobic rods that are motile by polar flagella. Pseudomonas includes a large number of species isolated from a variety of natural sources including soil, plants, water and clinical specimens, and has become a very heterogeneous taxon that is characterized by a high level of metabolic diversity (Rosselló et al., 1991;Palleroni, 2005).With the application of modern taxonomic techniques, including rRNA-DNA hybridization studies (Palleroni, 1984) and phylogenetic studies based on 16S rRNA gene sequence comparisons (Moore et al., 1996;Anzai et al., 2000), the genus Pseudomonas has been split into several genera, some even belonging to different subclasses in the phylum 'Proteobacteria', to accommodate bacteria originally described as species of Pseudomonas. In spite of this, the genus Pseudomonas sensu stricto comprises 120 species with names that have been validly published (http://www. bacterio.cict.fr; Yarza et al., 2010). Based on partial sequences of four housekeeping genes (16S rRNA, gyrB, rpoB and rpoD), Mulet et al. (2010) have recently identified two main intrageneric groups (IG) among species of the genus Pseudomonas, called IG Pseudomonas aeruginosa and IG Pseudomonas fluorescens. In their study, some species were placed on phylogenetic branches apart from both lineages, namely Pseudomonas oryzihabitans, Pseudomonas psychrotolerans, Pseudomonas luteola, Pseudomonas pertucinogena and Pseudomonas pachastrellae; among them, the last two always formed the deepest branch. Although not considered in the study by Mulet et al. (2010), other recently described species closely related to P. pertucinogena (Kawai & Yabuuchi, 1975) and P. pachastrellae (Romanenko et al., 2005) (Palleroni, 2005), three of thes...