Lactobacillus casei, L. paracasei, and L. rhamnosus form a closely related taxonomic group (Lactobacillus casei group) within the facultatively heterofermentative lactobacilli. Here, we report the complete genome sequences of L. paracasei JCM 8130 and L. casei ATCC 393, and the draft genome sequence of L. paracasei COM0101, all of which were isolated from daily products. Furthermore, we re-annotated the genome of L. rhamnosus ATCC 53103 (also known as L. rhamnosus GG), which we have previously reported. We confirmed that ATCC 393 is distinct from other strains previously described as L. paracasei. The core genome of 10 completely sequenced strains of the L. casei group comprised 1,682 protein-coding genes. Although extensive genome-wide synteny was found among the L. casei group, the genomes of ATCC 53103, JCM 8130, and ATCC 393 contained genomic islands compared with L. paracasei ATCC 334. Several genomic islands, including carbohydrate utilization gene clusters, were found at the same loci in the chromosomes of the L. casei group. The spaCBA pilus gene cluster, which was first identified in GG, was also found in other strains of the L. casei group, but several L. paracasei strains including COM0101 contained truncated spaC gene. ATCC 53103 encoded a higher number of proteins involved in carbohydrate utilization compared with intestinal lactobacilli, and extracellular adhesion proteins, several of which are absent in other strains of the L. casei group. In addition to previously fully sequenced L. rhamnosus and L. paracasei strains, the complete genome sequences of L. casei will provide valuable insights into the evolution of the L. casei group.

A labile selenium donor compound monoselenophosphate is synthesized from selenide and ATP by selenophosphate synthetase (SPS). In the present study, Sps1 and Sps2 were cloned from a cDNA library prepared from human lung adenocarcinoma cells (NCI-H441). The human lung Sps1 has been cloned as an ORF of 1,179 bp, identical in sequence to that of the recently revised human liver Sps1. The in-frame TGA codon of the lung Sps2 was genetically altered to TGT (Cys) to obtain the Sps2Cys gene. Expression of the recombinant plasmids containing Sps1 or Sps2Cys was highly toxic to Escherichia coli host cells grown aerobically. Accordingly, the human lung Sps homologs were characterized by an in vivo complementation assay using a selD mutant strain. An added selenium source and a low salt concentration (0.1-0.25% NaCl) in the medium were required for reproducible and sensitive in vivo complementation. Sps2Cys effectively complemented the selD mutant, and the resulting formate dehydrogenase H activity was as high as that of WT E. coli MC4100. In contrast, only a weak complementation of the selD mutant by the Sps1 gene was observed when cells were grown in selenite media. Better complementation with added L-selenocysteine suggested involvement of a selenocysteine lyase for mobilization of selenium. Based on this apparent substrate specificity of the Sps1 and Sps2 gene products we suggest that the Sps1-encoded enzyme depends on a selenium salvage system that recycles L-selenocysteine, whereas the Sps2 enzyme can function with a selenite assimilation system. I n many biological systems, the concentration of sulfurcontaining compounds is on the order of 1,000 times greater than their selenium analogs (1). Thus a selenium-specific pathway for biosynthesis of proteins that contain selenocysteine (SeCys) residues inserted as directed by the UGA codon is required. In Escherichia coli the insertion of selenium into selenium-dependent enzymes and Se-containing tRNAs requires the participation of the selD gene product (2). This protein, later identified as selenophosphate synthetase (SPS), forms a highly reactive, reduced selenium compound, monoselenophosphate (3). Monoselenophosphate is the product of the reaction catalyzed by SPS in which the ␥-phosphoryl group of ATP is transferred to selenide and inorganic phosphate and AMP are formed (4, 5). The mechanism of this reaction has yet to be determined. The identification of an essential cysteine residue, Cys-17, in the N-terminal glycine-rich region of the E. coli enzyme (SELD) has led to the assumption that this residue behaves as a nucleophile in the hydrolysis of ATP (6, 7 The E. coli selD gene product and its homologs present in mammals and Drosophila can be divided into two major groups. One group of SPS enzymes, which have a cysteine or SeCys residue at the site corresponding to Cys-17 in E. coli SELD, can catalyze the selenide-dependent formation of monoselenophosphate in vitro (3, 4, 9, 10). Replacement of Cys-17 with serine results in the complete loss of activity with ATP and s...

No abstract