Characteristics of Thiobacillus thioparus and its thiocyanate assimilation.

Thiocyanate-assimilatig bacterium, TK 21, was isolated from activated sludge used for the treatment of thiocyanate contained in coke-oven liquor. This organism oxidized thiosulfate and elemental sulfur, causing a decrease of pH of the medium. These facts indicated that it belongs to the genus Thiobacillus. Potassium thiocyanate (0.5 g/l) was completely assimilated during 60 h. Thiosulfate inhibited the assimilation of thiocyanate but elemental sulfur did not. This bacterium did not evolve cyanide as its oxidation product after the decomposition of thiocyanate. The isoalted bacterium was identified as Thiobacillus thioparus. Examination of the composition of cellular fatty acid of three strains of T. thioparus showed that they prossessed 3-hydroxy fatty acid of C10 and C12; saturated straight chains of C10, C12, C15, C16, C17, and C18; monounsaturated straight chains of C16 and C18; and cyclopropane acid of C17.     

Procedure for the efficient acquisition of progeny seeds from crossed potato plants grafted onto tomato

Potato, Solanum tuberosum L. is an important crop. However, it is difficult to breed potato cultivars by applying conventional crossing methods because potato has a tetraploid genome and is vegetatively propagated. Flower formation and tuber development occur simultaneously. Many potato cultivars hardly produce any fruits after crossing and fail to produce seeds. We report an improved procedure for obtaining progeny seeds by grafting potatoes onto tomatoes. The rate of fruit formation was more than 19% when the grafted potatoes were used for the crossing experiments, whereas crossing using the ungrafted plants showed a rate of 1.1%. This result suggests that our procedure results in the easy acquisition of null-segregant progenies by crossing mutant lines. It is also expected to improve conventional potato breeding.     

Identification of asymptomatic Entamoeba histolytica infection by a serological screening test: A cross-sectional study of an HIV-negative men who have sex with men cohort in Japan

BackgroundAmebiasis, caused by Entamoeba histolytica, is spreading in developing countries and in many developed countries as a sexually transmitted infection. Here, we evaluated the efficacy of serological screening to identify asymptomatic E. histolytica infection as a potential epidemiological control measure to limit its spread.Methodology/Principal findingsThis cross-sectional study was carried out between January and March 2021 in an HIV-negative men who have sex with men (MSM) cohort at the National Center for Global Health and Medicine. Serological screening was performed using a commercially available ELISA kit. For seropositive individuals, we performed stool polymerase chain reaction (PCR) to determine current E. histolytica infection. We performed E. histolytica serological screening of 312 participants. None had a history of E. histolytica infection prior to the study. The overall E. histolytica seropositivity was 6.7% (21/312), which was similar to that found by the rapid plasma reagin test (17/312). We identified current infection in 8 of 20 seropositive participants (40.0%) by stool PCR.Conclusions/SignificanceOur serological screening approach constitutes a potentially practical epidemiological strategy. Active epidemiological surveys, in combination with an effective screening strategy for asymptomatically infected individuals, should be applied to help reduce sexually transmitted E. histolytica infections.     

Concerted actions of DnaA complexes with DNA-unwinding sequences within and flanking replication origin oriC promote DnaB helicase loading

Unwinding of the replication origin and loading of DNA helicases underlie the initiation of chromosomal replication. In Escherichia coli, the minimal origin oriC contains a duplex unwinding element (DUE) region and three (Left, Middle, and Right) regions that bind the initiator protein DnaA. The Left/Right regions bear a set of DnaA-binding sequences, constituting the Left/Right-DnaA subcomplexes, while the Middle region has a single DnaA-binding site, which stimulates formation of the Left/Right-DnaA subcomplexes. In addition, a DUE-flanking AT-cluster element (TATTAAAAAGAA) is located just outside of the minimal oriC region. The Left-DnaA subcomplex promotes unwinding of the flanking DUE exposing TT[A/G]T(T) sequences that then bind to the Left-DnaA subcomplex, stabilizing the unwound state required for DnaB helicase loading. However, the role of the Right-DnaA subcomplex is largely unclear. Here, we show that DUE unwinding by both the Left/Right-DnaA subcomplexes, but not the Left-DnaA subcomplex only, was stimulated by a DUE-terminal subregion flanking the AT-cluster. Consistently, we found the Right-DnaA subcomplex–bound single-stranded DUE and AT-cluster regions. In addition, the Left/Right-DnaA subcomplexes bound DnaB helicase independently. For only the Left-DnaA subcomplex, we show the AT-cluster was crucial for DnaB loading. The role of unwound DNA binding of the Right-DnaA subcomplex was further supported by in vivo data. Taken together, we propose a model in which the Right-DnaA subcomplex dynamically interacts with the unwound DUE, assisting in DUE unwinding and efficient loading of DnaB helicases, while in the absence of the Right-DnaA subcomplex, the AT-cluster assists in those processes, supporting robustness of replication initiation.

The initiation of bacterial DNA replication requires local duplex unwinding of the chromosomal replication origin oriC, which is regulated by highly ordered initiation complexes. In Escherichia coli, the initiation complex contains oriC, the ATP-bound form of the DnaA initiator protein (ATP–DnaA), and the DNA-bending protein IHF (Fig. 1, A and B), which promotes local unwinding of oriC (1, 2, 3, 4). Upon this oriC unwinding, two hexamers of DnaB helicases are bidirectionally loaded onto the resultant single-stranded (ss) region with the help of the DnaC helicase loader (Fig. 1B), leading to bidirectional chromosomal replication (5, 6, 7, 8). However, the fundamental mechanism underlying oriC-dependent bidirectional DnaB loading remains elusive.Open in a separate windowFigure 1Schematic structures of oriC, DnaA, and the initiation complexes. A, the overall structure of oriC. The minimal oriC region and the AT-cluster region are indicated. The sequence of the AT-cluster−DUE (duplex-unwinding element) region is also shown below. The DUE region (DUE; pale orange bars) contains three 13-mer repeats: L-DUE, M-DUE, and R-DUE. DnaA-binding motifs in M/R-DUE, TT(A/G)T(T), are indicated by red characters. The AT-cluster region (AT cluster; brown bars) is flanked by DUE outside of the minimal oriC. The DnaA-oligomerization region (DOR) consists of three subregions called Left-, Middle-, and Right-DOR. B, model for replication initiation. DnaA is shown as light brown (for domain I–III) and darkbrown (for domain IV) polygons (right panel). ATP–DnaA forms head-to-tail oligomers on the Left- and Right-DORs (left panel). The Middle-DOR (R2 box)-bound DnaA interacts with DnaA bound to the Left/Right-DORs using domain I, but not domain III, stimulating DnaA assembly. IHF, shown as purple hexagons, bends DNA >160° and supports DUE unwinding by the DnaA complexes. M/R-DUE regions are efficiently unwound. Unwound DUE is recruited to the Left-DnaA subcomplex and mainly binds to R1/R5M-bound DnaA molecules. The sites of ssDUE-binding B/H-motifs V211 and R245 of R1/R5M-bound DnaA molecules are indicated (pink). Two DnaB homohexamer helicases (light green) are recruited and loaded onto the ssDUE regions with the help of the DnaC helicase loader (cyan). ss, single stranded.The minimal oriC region consists of the duplex unwinding element (DUE) and the DnaA oligomerization region (DOR), which contains specific arrays of 9-mer DnaA-binding sites (DnaA boxes) with the consensus sequence TTA[T/A]NCACA (Fig. 1A) (3, 4). The DUE underlies the local unwinding and contains 13-mer AT-rich sequence repeats named L-, M-, and R-DUE (9). The M/R-DUE region includes TT[A/G]T(A) sequences with specific affinity for DnaA (10). In addition, a DUE-flanking AT-cluster (TATTAAAAAGAA) region resides just outside of the minimal oriC (Fig. 1A) (11). The DOR is divided into three subregions, the Left-, Middle-, and Right-DORs, where DnaA forms structurally distinct subcomplexes (Fig. 1A) (8, 12, 13, 14, 15, 16, 17). The Left-DOR contains high-affinity DnaA box R1, low-affinity boxes R5M, τ1−2, and I1-2, and an IHF-binding region (17, 18, 19, 20). The τ1 and IHF-binding regions partly overlap (17).In the presence of IHF, ATP–DnaA molecules cooperatively bind to R1, R5M, τ2, and I1-2 boxes in the Left-DOR, generating the Left-DnaA subcomplex (Fig. 1B) (8, 17). Along with IHF causing sharp DNA bending, the Left-DnaA subcomplex plays a leading role in DUE unwinding and subsequent DnaB loading. The Middle-DOR contains moderate-affinity DnaA box R2. Binding of DnaA to this box stimulates DnaA assembly in the Left- and Right-DORs using interaction by DnaA N-terminal domain (Fig. 1B; also see below) (8, 12, 14, 16, 21). The Right-DOR contains five boxes (C3-R4 boxes) and cooperative binding of ATP–DnaA molecules to these generates the Right-DnaA subcomplex (Fig. 1B) (12, 18). This subcomplex is not essential for DUE unwinding and plays a supportive role in DnaB loading (8, 15, 17). The Left-DnaA subcomplex interacts with DnaB helicase, and the Right-DnaA subcomplex has been suggested to play a similar role (Fig. 1B) (8, 13, 16).In the presence of ATP–DnaA, M- and R-DUE adjacent to the Left-DOR are predominant sites for in vitro DUE unwinding: unwinding of L-DUE is less efficient than unwinding of the other two (Fig. 1B) (9, 22, 23). Deletion of L-DUE or the whole DUE inhibits replication of oriC in vitro moderately or completely, respectively (23). A chromosomal oriC Δ(AT-cluster−L-DUE) mutant with an intact DOR, as well as deletion of Right-DOR, exhibits limited inhibition of replication initiation, whereas the synthetic mutant combining the two deletions exhibits severe inhibition of cell growth (24). These studies suggest that AT-cluster−L-DUE regions stimulate replication initiation in a manner concerted with Right-DOR, although the underlying mechanisms remain elusive.DnaA consists of four functional domains (Fig. 1B) (4, 25). Domain I supports weak domain I–domain I interaction and serves as a hub for interaction with various proteins such as DnaB helicase and DiaA, which stimulates ATP–DnaA assembly at oriC (26, 27, 28, 29, 30). Two or three domain I molecules of the oriC–DnaA subcomplex bind a single DnaB hexamer, forming a stable higher-order complex (7). Domain II is a flexible linker (28, 31). Domain III contains AAA+ (ATPase associated with various cellular activities) motifs essential for ATP/ADP binding, ATP hydrolysis, and DnaA–DnaA interactions in addition to specific sites for ssDUE binding and a second, weak interaction with DnaB helicase (1, 4, 8, 10, 19, 25, 32, 33, 34, 35). Domain IV bears a helix-turn-helix motif with specific affinity for the DnaA box (36).As in typical AAA+ proteins, a head-to-tail interaction underlies formation of ATP–DnaA pentamers on the DOR, where the AAA+ arginine-finger motif Arg285 recognizes ATP bound to the adjacent DnaA protomer, promoting cooperative ATP–DnaA binding (Fig. 1B) (19, 32). DnaA ssDUE-binding H/B-motifs (Val211 and Arg245) in domain III sustain stable unwinding by directly binding to the T-rich (upper) strand sequences TT[A/G]T(A) within the unwound M/R-DUE (Fig. 1B) (8, 10). Val211 residue is included in the initiator-specific motif of the AAA+ protein family (10). For DUE unwinding, ssDUE is recruited to the Left-DnaA subcomplex via DNA bending by IHF and directly interacts with H/B-motifs of DnaA assembled on Left-DOR, resulting in stable DUE unwinding competent for DnaB helicase loading; in particular, DnaA protomers bound to R1 and R5M boxes play a crucial role in the interaction with M/R-ssDUE (Fig. 1B) (8, 10, 17). Collectively, these mechanisms are termed ssDUE recruitment (4, 17, 37).Two DnaB helicases are thought to be loaded onto the upper and lower strands of the region including the AT-cluster and DUE, with the aid of interactions with DnaC and DnaA (Fig. 1B) (25, 38, 39). DnaC binding modulates the closed ring structure of DnaB hexamer into an open spiral form for entry of ssDNA (40, 41, 42, 43). Upon ssDUE loading of DnaB, DnaC is released from DnaB in a manner stimulated by interactions with ssDNA and DnaG primase (44, 45). Also, the Left- and Right-DnaA subcomplexes, which are oriented opposite to each other, could regulate bidirectional loading of DnaB helicases onto the ssDUE (Fig. 1B) (7, 8, 35). Similarly, recent works suggest that the origin complex structure is bidirectionally organized in both archaea and eukaryotes (1, 46). In Saccharomyces cerevisiae, two origin recognition complexes containing AAA+ proteins bind to the replication origin region in opposite orientations; this, in turn, results in efficient loading of two replicative helicases, leading to head-to-head interactions in vitro (46). Consistent with this, origin recognition complex dimerization occurs in the origin region during the late M-G1 phase (47). The fundamental mechanism of bidirectional origin complexes might be widely conserved among species.In this study, we analyzed various mutants of oriC and DnaA in reconstituted systems to reveal the regulatory mechanisms underlying DUE unwinding and DnaB loading. The Right-DnaA subcomplex assisted in the unwinding of oriC, dependent upon an interaction with L-DUE, which is important for efficient loading of DnaB helicases. The AT-cluster region adjacent to the DUE promoted loading of DnaB helicase in the absence of the Right-DnaA subcomplex. Consistently, the ssDNA-binding activity of the Right-DnaA subcomplex sustained timely initiation of growing cells. These results indicate that DUE unwinding and efficient loading of DnaB helicases are sustained by concerted actions of the Left- and Right-DnaA subcomplexes. In addition, loading of DnaB helicases are sustained by multiple mechanisms that ensure robust replication initiation, although the complete mechanisms are required for precise timing of initiation during the cell cycle.     

The enterotoxin gene (cpe) of Clostridium perfringens can be chromosomal or plasmid-borne

The location of the cpe gene, encoding the enterotoxin responsible for food poisoning in humans, has been studied in a series of enterotoxigenic Ciostridium perfringens strains by means of pulsed field gel electrophoresis of genomic DNA. The cpe gene was found at the same chromosomal locus in strains associated with food poisoning in humans and was shown to be linked to a repetitive sequence, the Hin dlll repeat, and an open reading frame, ORF3, that may be part of an insertion sequence. In contrast, when the strains originated from domesticated livestock cpe was located on a large episome where it was often close to a copy of the transposable element IS 1151. In these cases, the Hin dlll repeat was not linked to the cpe gene although this was generally preceded by ORF3.     

Phospholipase D production using immobilized cells of Streptoverticillium cinnamoneum

Summary Production of phospholipase D (PLD) by Streptoverticillium cinnamoneum immobilized within porous particles was investigated in repeated batch fermentation. The enzyme productivity in repeated batch fermentation was 2.2-fold that obtained in batch fermentation without immobilization, since many of the immobilized cells could be utilized as seed cells for each subsequent batch cycle.     

Pituitary adenylate cyclase-activating polypeptide promotes differentiation of mouse neural stem cells into astrocytes

We have found that pituitary adenylate cyclase-activating polypeptide (PACAP) employed at the physiological concentrations induces the differentiation of mouse neural stem cells into astrocytes. The differentiation process was not affected by cAMP analogues such as dibutylic cAMP (db-cAMP) or 8Br-cAMP or by the specific competitive inhibitor of protein kinase A, Rp-adenosine-3',5'-cyclic monophosphothioate triethylamine salt (Rp-cAMP). Expression of the PACAP receptor (PAC1) in neural stem cells was detected by both RT-PCR and immunoblot using an affinity-purified antibody. The PACAP selective antagonist, PACAP(6-38), had an inhibitory effect on the PACAP-induced differentiation of neural stem cells into astrocytes. These results indicate that PACAP acts on the PAC1 receptor on the plasma membrane of mouse neural stem cells, with the signal then transmitted intracellularly via a PAC1-coupled G protein, does not involve Gs. This signaling mechanism may thus play a crucial role in the differentiation of neural stem cells into astrocytes.     

Regulation of gonadotropin secretion and puberty onset by neuromedin U

Neuromedin U (NMU), an anorexigenic peptide, was originally isolated from porcine spinal cord in 1985. As NMU is abundant in the anterior pituitary gland, we investigated the effects of NMU on gonadotropin secretion. Both NMU and its receptors, NMUR1 and NMUR2, were expressed in the pituitary gland. NMU suppressed LH and FSH releases from rat anterior pituitary cells. Moreover, NMU-deficient mice exhibit an early onset of vaginal opening. The LHbeta/FSHbeta ratio, which is an index of puberty onset, is high in young NMU-deficient mice. These results indicate that NMU suppresses gonadotropin secretion and regulates the onset of puberty.     

Severe hypercholesterolemia,impaired fat tolerance,and advanced atherosclerosis in mice lacking both low density lipoprotein receptor-related protein 5 and apolipoprotein E

LDL receptor-related protein 5 (LRP5) plays multiple roles, including embryonic development and bone accrual development. Recently, we demonstrated that LRP5 is also required for normal cholesterol metabolism and glucose-induced insulin secretion. To further define the role of LRP5 in the lipoprotein metabolism, we compared plasma lipoproteins in mice lacking LRP5, apolipoprotein E (apoE), or both (apoE;LRP5 double knockout). On a normal chow diet, the apoE;LRP5 double knockout mice (older than 4 months of age) had approximately 60% higher plasma cholesterol levels compared with the age-matched apoE knockout mice. In contrast, LRP5 deficiency alone had no significant effects on the plasma cholesterol levels. High performance liquid chromatography analysis of plasma lipoproteins revealed that cholesterol levels in the very low density lipoprotein and low density lipoprotein fractions were markedly increased in the apoE;LRP5 double knockout mice. There were no apparent differences in the pattern of apoproteins between the apoE knockout mice and the apoE;LRP5 double knockout mice. The plasma clearance of intragastrically loaded triglyceride was markedly impaired by LRP5 deficiency. The atherosclerotic lesions of the apoE;LRP5 double knockout mice aged 6 months were approximately 3-fold greater than those in the age-matched apoE-knockout mice. Furthermore, histological examination revealed highly advanced atherosclerosis, with remarkable accumulation of foam cells and destruction of the internal elastic lamina in the apoE;LRP5 double knockout mice. These data suggest that LRP5 mediates both apoE-dependent and apoE-independent catabolism of plasma lipoproteins.