Complete genome sequence of Arcticibacterium luteifluviistationis SM1504T, a cytophagaceae bacterium isolated from Arctic surface seawater

Arcticibacterium luteifluviistationis SM1504T was isolated from Arctic surface seawater and classified as a novel genus of the phylum Bacteroides. To date, no Arcticibacterium genomes have been reported, their genomic compositions and metabolic features are still unknown. Here, we reported the complete genome sequence of A. luteifluviistationis SM1504T, which comprises 5,379,839 bp with an average GC content of 37.20%. Genes related to various stress (such as radiation, osmosis and antibiotics) resistance and gene clusters coding for carotenoid and flexirubin biosynthesis were detected in the genome. Moreover, the genome contained a 245-kb genomic island and a 15-kb incomplete prophage region. A great percentage of proteins belonging to carbohydrate metabolism especially in regard to polysaccharides utilization were found. These related genes and metabolic characteristics revealed genetic basis for adapting to the diverse extreme Arctic environments. The genome sequence of A. luteifluviistationis SM1504T also implied that the genus Arcticibacterium may act as a vital organic carbon matter decomposer in the Arctic seawater ecosystem.


Introduction
As the third most abundant bacterial group in the seawater system, phylum Bacteroidetes plays a vital role in diverse oceanic biogeochemical processes [1]. It has been reported that phylum Bacteroidetes could mediate the degradation of HMW compounds especially in the respect of algal organic matter [2,3]. Many heterotrophic microorganisms such as the SAR11 clade and marine Gammaproteobacteria grow partly due to phylum Bacteroidetes-derived organic products [4,5]. Thus, phylum Bacteroidetes groups may play crucial roles in the nutrient utilization and cycling in the seawater ecosystem.
The family Cytophagaceae, currently comprising 31 genera, is one of the largest groups in the phylum Bacteroidetes [6]. The species in the family Cytophagaceae have been isolated from various habitats including freshwater river [7], seawater [8], permafrost soil [9] and even polar glacial till [10]. The genus Arcticibacterium, belonging to the family Cytophagaceae, accommodates only one recognized species: A. luteifluviistationis SM1504 T (=KCTC 42716 T =CCTCC AB 2015348 T ) [11]. Strain SM1504 T was isolated from surface seawater of King's Fjord, Arctic. However, to date, no genomes of the genus Arcticibacterium have been reported, their genomic compositions and metabolic pathways are still lacking. In the study, we reported the first genome sequence of the genus Arcticibacterium to better understand its survival strategy and ecological niche in the Arctic seawater.

Classification and features
As the type strain of A. luteifluviistationis in the family Cytophagaceae, strain SM1504 T is a Gram-negative, aerobic, non-motile and rod bacterium (Fig. 1). The yellow-pigmented colony was found after incubation at 20°C for 2 days on a TYS agar plate. The strain could utilize glycerol, D-xylose, D-glucose, D-fructose, dulcitol, inositol D-mannitol, D-sorbitol, N-acetylglucosamine, arbutin, aesculin, cellobiose, maltose, sucrose, trehalose, starch, turanose and potassium gluconate for energy and growth, which were summarized in Table 1. Then it hydrolyzed aesculin, gelatin, tyrosine, Tween 20, 40 and 60 but did not hydrolyze DNA, agar, casein, elastin, lecithin, starch, Tween 80. In addition, various enzymes such as alkaline phosphatase, esterase (C4), esterase lipase (C8), leucine arylamidase, valine arylamidase, cystine arylamidase, trypsin and glucosidase were produced for degrading organic matter [11]. The phylogenetic placement of strain SM1504 T (based on complete 16S rRNA gene sequence) through neighbor-joining phylogenetic tree was identified (Fig. 2). It formed a distinct phylogenetic branch within the family Cytophagaceae and closely relatives were species of the genera Lacihabitans, Emticicia, Fluviimonas and Leadbetterella with low sequence similarities between 88.9 and 91.6%.

Genome project history
Isolated from an extreme Arctic environment, A. luteifluviistationis SM1504 T was selected for genome sequencing to elucidate the special abilities of adapting to diverse extreme stresses. We have accomplished the genome sequencing of strain SM1504 T as reported in this paper. The complete genome data has been deposited in the GenBank database under the accession number CP029480.1. The project information and its association with MIGS are provided in Table 2 [12].

Genome properties
The total size of the genome of A. luteifluviistationis SM1504 T is 5,379,839 bp with an average GC content of 37.20% (Fig. 3). Total 4595 protein-coding genes (CDSs) were identified, which occupied 89.73% of the genome.
Therein, 3045 CDSs were annotated with putative functions and 1550 CDSs matched hypothetical proteins (Table 3). Then 4 rRNAs and 36 tRNAs were found in the genome. CRISPR repeat, transmembrane helice, signal peptide and Pfam protein family predictions were  done. In addition, distribution of genes into COG functional categories was shown in Table 4.

Insights from the genome sequence
Adaption to diverse stresses Strain SM1504 T genome owned two putative gene clusters for secondary metabolite biosynthesis. The cluster 1 belonged to terpene type -the largest group of natural products [22], matching the carotenoid biosynthesis. The cluster 2, affiliated to arylpolyene type, was predicted to produce flexirubin. Furthermore, we found that the yellow-pigmented strain SM1504 T harbors a complete set of genes required for zeaxanthin biosynthesis (e.g., isopentenyl-diphosphate deltaisomerase, phytoene synthase, phytoene dehydrogenase, lycopene cyclase and beta-carotene hydroxylase), which was commonly detected in other species of the phylum Bacteroidetes [23,24]. The pigment maybe help the strain to obtain energy and for cold adaption and ultraviolet light protection in the Arctic environments [25]. A total of 150 resistance genes were found to encode 24 kinds of antibiotics (such as gentamicin, kanamycin, tetracycline and streptomycin), which was consistent with the experimental antibiotic susceptibility results [11]. The genes encoding heat shock proteins dnaK and cold shock protein cspA were detected in the genome. In line with this, SM1504 T had a wider growth temperature ranges (4-30°C) [11]. Besides, the genome harbored several genes coding for catalase and superoxide dismutase to assist the strain at cellular and molecular levels in dealing harsh radiation in the Arctic. Dozens of genes related to osmotic stress (such as choline and betaine uptake and betaine biosynthesis) and carbon starvation responses were discovered in the A. luteifluviistationis genome, which would endow cells with tolerance to hyperhaline and oligotrophic environments.
As another feature, a 245-kb genomic island coding for 208 genes was predicted. Therein, 9 genes encoded proteins related to glucide biosynthesis, such aslipopolysaccharide core biosynthesis glycosyltransferase (lpsD), UDP-glucose dehydrogenase and capsular polysaccharide synthesis enzyme (Cap8C). In addition, the presence of transposases, integrases and mobile element proteins indicated that gene transfer has occurred in the A. luteifluviistationis SM1504 T genome [26]. Also, phage tail fiber proteins were predicted, which was in line with the The total is based on the total number of protein coding genes in the genome analysis by PHAST [27] that a 15-kb incomplete prophage region could encode phage tail fiber proteins in the genome.

Degradation and utilization of carbohydrates
Totally, 3319 (71.61%) genes could be assigned a COG function, of which the wall/membrane/envelope biogenesis (5.89%), carbohydrate transport and metabolism (4.94%) and inorganic ion transport and metabolism (4.83%) were enriched (

Conclusions
The genomic analyses showed that the strain SM1504 T could adapt to extreme Arctic seawater environments, such as high solar radiation, cold temperature and high salinity. Besides, it may act as a vital macromolecular polysaccharide decomposer and would play an important role in organic carbon cycling in the Arctic seawater ecosystem.