Complete genome sequence of Halopiger xanaduensis type strain (SH-6T)

Halopiger xanaduensis is the type species of the genus Halopiger and belongs to the euryarchaeal family Halobacteriaceae. H. xanaduensis strain SH-6, which is designated as the type strain, was isolated from the sediment of a salt lake in Inner Mongolia, Lake Shangmatala. Like other members of the family Halobacteriaceae, it is an extreme halophile requiring at least 2.5 M salt for growth. We report here the sequencing and annotation of the 4,355,268 bp genome, which includes one chromosome and three plasmids. This genome is part of a Joint Genome Institute (JGI) Community Sequencing Program (CSP) project to sequence diverse haloarchaeal genomes.


Introduction
Halopiger xanaduensis is the type species of the genus Halopiger, and strain SH-6 is the type strain of the species. It was isolated from the sediment of a salt lake, Lake Shangmatala, in Inner Mongolia, China [1]. The name Halopiger refers to its slow growth in the laboratory. There is one other described species in the genus Halopiger, H. aswanensis, which was isolated from a saline soil in Egypt [2]. We report here the first genome sequence from the genus Halopiger.

Classification and features
In 16S rRNA trees the Halopiger species are most closely related to Natronolimnobius species [1,2]. Currently there are fifteen complete genomes of haloarchaea in GenBank. Figure 1 shows the relationship of H. xanaduensis to other haloarchaea for which complete genomes have been sequenced. For Halobacterium salinarum and Haloquadratum walsbyi, only one sequence is included in Figure 1, although for both of these species two genomes have been sequenced.
H. xanaduensis was isolated from a sediment sample of Lake Shangmatala in Inner Mongolia, China. The sample was enriched in liquid medium containing salts and yeast extract; the culture was then plated on agar to obtain pure colonies [1]. At the time of sample collection, the salinity of the lake was 16.7%, the temperature was 21.8°C, and the pH was 8.5 [1]. The cells were pleomorphic with the most common shape being rods. Motility was not observed [1]. An electron micrograph is shown in Figure 2. Growth was observed between 28 and 45°C with an optimum at 37°C [1]. The pH range for growth was 6.0-11.0 with an optimal pH of 7.5-8.0 [1]. Growth occurred within a salinity range of 2.5 M to 5.0 M NaCl and was optimal at 4.3M NaCl [1]. The organism is strictly aerobic but was able to reduce nitrate and nitrite with production of gas [1]. Several sugars and amino acids can serve as sole carbon and energy sources, and amino acids are not required in the growth medium [1]. The features of the organism are listed in Table 1.  [3], which uses the Jukes-Cantor corrected distance model to construct a distance matrix based on alignment model positions without the use of alignment inserts, and uses a minimum comparable position of 200. The tree was generated with the Tree Builder from the RDP which uses Weighbor [4] with an alphabet size of 4 and length size of 1,000. The building of the tree also involves a bootstrapping process repeated 100 times to generate a majority consensus tree. Methanosarcina acetivorans was used as the outgroup.  Phylum Euryarchaeota TAS [7] Class Halobacteria TAS [8,9] Current classification Order Halobacteriales TAS [10][11][12] Family Halobacteriaceae TAS [13,14] Genus Altitude not reported a) Evidence codes -TAS: Traceable Author Statement (i.e., a direct report exists in the literature); NAS: Non-traceable Author Statement (i.e., not directly observed for the living, isolated sample, but based on a generally accepted property for the species, or anecdotal evidence). These evidence codes are from the Gene Ontology project [15]. Standards in Genomic Sciences

Genome sequencing information
Genome project history H. xanaduensis was selected for sequencing as part of a JGI CSP project to sequence a representative from every genus of haloarchaea. The genome project is listed in the Genomes On Line Database [16], and the complete genome sequence has been deposited in GenBank. Sequencing was carried out at the JGI Production Genomics Facility (PGF).
Finishing was done at Los Alamos National Laboratory. Annotation was done at both the PGF and Oak Ridge National Laboratory. Table 2 presents the project information and its association with MIGS version 2.0 compliance [5].

Genome sequencing and assembly
The draft genome of Halopiger xanaduensis SH-6 was generated at the DOE Joint genome Institute (JGI) using a combination of Illumina [18] and 454 technologies [19].

Genome annotation
Genes were identified using Prodigal [26], followed by a round of manual curation using GenePRIMP [27].

Genome properties
The genome includes one circular chromosome and three plasmids, for a total size of 4,355,268 bp ( Table 3, Table 4). A map of the chromosome is shown in Figure 3 and maps of the plasmids are shown in Figures 4, 5, and 6. A total of 4,370 genes were predicted, 4,310 of which are protein-coding genes and 60 of which are RNA genes. There are three ribosomal RNA operons with one additional copy of 5S rRNA. Putative functions were assigned to 2,560 protein coding genes, with the remaining genes annotated as hypothetical proteins. There are 89 pseudogenes, accounting for 2.06% of protein-coding genes. Table 5 shows the distribution of genes in COG categories. a) The total is based on either the size of the genome in base pairs or the total number of protein coding genes in the annotated genome. Standards in Genomic Sciences

Genome analysis
H. xanaduensis grows on only a few of the carbohydrates that were tested (glucose, galactose, and xylose) [1], but surprisingly it has 40 glycosyl hydrolases and 5 polysaccharide lyases [32]. It also has quite a large number of ABC transporters for carbohydrates: 10 full transporters and one additional substrate-binding protein. Among the sequenced haloarchaea, only Haloferax volcanii has a greater number of carbohydrate ABC transporters [33]. Taken together, these findings suggest that H. xanaduensis is capable of growth on other sugars that have not been tested.
While many of the glycosyl hydrolases have no characterized close homologs, for some of them, functions can be predicted. Halxa_0484 has 73% similarity to beta-galactosidase of Haloferax lucentense [34], while Halxa_3778 has 75% similarity to a xylanase from Streptomyces sp. S27 [35]. Two of the polysaccharide lyases from family PL11 have greater than 65% similarity to rhamnogalacturonan lyases YesW and YesX from Bacillus subtilis [36], suggesting that H. xanaduensis may be capable of pectin degradation. Degradation pathways for the three sugars that H. xanaduensis is known to utilize can be identified in the genome. Glucose is likely degraded by the semiphosphorylated Entner-Doudoroff pathway as in other haloarchaea [37]. Three enzymes of the pathway, glucose dehydrogenase, gluconate dehydratase, and 2-keto-3-deoxyphosphogluconate aldolase, are found in an operon (Halxa_4119-4121). The 2-keto-3-deoxygluconate kinase is found elsewhere in the genome (Halxa_2064). Galactose is probably metabolized via the De Ley-Doudoroff pathway as a galactonate dehydratase is present (Halxa_3608). Adjacent to this gene are a possible alpha-galactosidase (Halxa_3609) and a kinase and aldolase that may take part in this pathway (Halxa_3607,  Halxa_3606). Xylose utilization appears to be via the pathway found in H. volcanii [38] which results in formation of 2-oxoglutarate. Again three enzymes of the pathway form an operonxylonate dehydratase, 2-keto-3-deoxyxylonate dehydratase, and 2,5-dioxopentanoate dehydrogenase (Halxa_3763-3765). Despite the fact that it was isolated from lake sediment, H. xanaduensis has an operon of gas vesicle proteins (Halxa_0820-0830). It is lacking GvpC, GvpD, GvpE, and GvpH, but mutation studies have shown that these four proteins are not required for gas vesicle formation [39], so H. xanaduensis can probably form functional gas vesicles. This suggests that H. xanaduensis may spend part of its life close to the surface of the lake. H. xanaduensis has several genes involved in polysaccharide synthesis and transport that are not found in any other sequenced haloarchaea. It has two genes (Halxa_0209, Halxa_2361) belonging to the Capsular Polysaccharide Exporter family (TC 9.A.41). This is unusual as one of the members of this family is thought to transport polysaccharide across the outer membrane of Gram-negative bacteria [40]. Adjacent to these two exporter genes are two genes (Halxa_0208, Halxa_2362) belonging to COG1861, cytidylyl transferases involved in polysaccharide biosynthesis. H. xanaduensis also has one gene (Halxa_2364) related to PseG, a UDP-sugar hydrolase involved in polysaccharide production [41]. The presence of these genes in H. xanaduensis suggests that it may be capable of extracellular polysaccharide synthesis using a process unlike any found in other haloarchaea. a) The total is based on the total number of protein coding genes in the annotated genome. Figure 6. Graphical circular map of plasmid pHALXA03. From outside to center: Genes on forward strand (colored by COG categories), genes on reverse strand (colored by COG categories), GC content, and GC skew.