HS Strain Research Articles

Arsenophonus and Sodalis replacements shape evolution of symbiosis in louse flies.

Symbiotic interactions between insects and bacteria are ubiquitous and form a continuum from loose facultative symbiosis to greatly intimate and stable obligate symbiosis. In blood-sucking insects living exclusively on vertebrate blood, obligate endosymbionts are essential for hosts and hypothesized to supplement B-vitamins and cofactors missing from their blood diet. The role and distribution of facultative endosymbionts and their evolutionary significance as seeds of obligate symbioses are much less understood. Here, using phylogenetic approaches, we focus on the Hippoboscidae phylogeny as well as the stability and dynamics of obligate symbioses within this bloodsucking group. In particular, we demonstrate a new potentially obligate lineage of Sodalis co-evolving with the Olfersini subclade of Hippoboscidae. We also show several likely facultative Sodalis lineages closely related to Sodalis praecaptivus (HS strain) and suggest repeated acquisition of novel symbionts from the environment. Similar to Sodalis, Arsenophonus endosymbionts also form both obligate endosymbiotic lineages co-evolving with their hosts (Ornithomyini and Ornithoica groups) as well as possibly facultative infections incongruent with the Hippoboscidae phylogeny. Finally, we reveal substantial diversity of Wolbachia strains detected in Hippoboscidae samples falling into three supergroups: A, B, and the most common F. Altogether, our results prove the associations between Hippoboscoidea and their symbiotic bacteria to undergo surprisingly dynamic, yet selective, evolutionary processes strongly shaped by repeated endosymbiont replacements. Interestingly, obligate symbionts only originate from two endosymbiont genera, Arsenophonus and Sodalis, suggesting that the host is either highly selective about its future obligate symbionts or that these two lineages are the most competitive when establishing symbioses in louse flies.

Sequencing a piece of history: complete genome sequence of the original Escherichia coli strain.

In 1885, Theodor Escherich first described the Bacillus coli commune, which was subsequently renamed Escherichia coli. We report the complete genome sequence of this original strain (NCTC 86). The 5 144 392 bp circular chromosome encodes the genes for 4805 proteins, which include antigens, virulence factors, antimicrobial-resistance factors and secretion systems, of a commensal organism from the pre-antibiotic era. It is located in the E. coli A subgroup and is closely related to E. coli K-12 MG1655. E. coli strain NCTC 86 and the non-pathogenic K-12, C, B and HS strains share a common backbone that is largely co-linear. The exception is a large 2 803 932 bp inversion that spans the replication terminus from gmhB to clpB. Comparison with E. coli K-12 reveals 41 regions of difference (577 351 bp) distributed across the chromosome. For example, and contrary to current dogma, E. coli NCTC 86 includes a nine gene sil locus that encodes a silver-resistance efflux pump acquired before the current widespread use of silver nanoparticles as an antibacterial agent, possibly resulting from the widespread use of silver utensils and currency in Germany in the 1800s. In summary, phylogenetic comparisons with other E. coli strains confirmed that the original strain isolated by Escherich is most closely related to the non-pathogenic commensal strains. It is more distant from the root than the pathogenic organisms E. coli 042 and O157 : H7; therefore, it is not an ancestral state for the species.

Chicken gga-miR-19a Targets ZMYND11 and Plays an Important Role in Host Defense against Mycoplasma gallisepticum (HS Strain) Infection.

Mycoplasma gallisepticum (MG), one of the most pathogenic Mycoplasmas, can cause chronic respiratory disease (CRD) in chickens. It has been suggested that micro-ribonucleic acids (miRNAs) are involved in microbial pathogenesis. However, little is known about the roles of miRNAs in MG infection. Previously, we found by deep sequencing that gga-miR-19a was significantly up-regulated in the lungs of MG-infected chicken embryos. In this work, we confirmed that gga-miR-19a was up-regulated in both MG-infected chicken embryonic lungs and MG-infected DF-1 (chicken embryo fibroblast) cells. At 72 h post-transfection, we found that the over-expression of gga-miR-19a significantly enhanced the proliferation of MG-infected DF-1 cells by promoting the transition from the G1 phase to the S and G2 phases, while a gga-miR-19a inhibitor repressed the proliferation of MG-infected DF-1 cells by arresting the cell cycle in the G1 phase. Moreover, we found that gga-miR-19a regulated the expression of the host zinc-finger protein, MYND-type containing 11 (ZMYND11), through binding to its 3′ untranslated region (3′-UTR). DAVID analysis revealed that ZMYND11 could negatively regulate the NF-kappaB (NF-κB) signaling pathway in chickens (Gallus gallus). Upon MG infection, gga-miR-19a, NF-κB, MyD88, and TNF-α were all up-regulated, whereas ZMYND11 was down-regulated. The over-expression of gga-miR-19a in the DF-1 cells did not affect the above gene expression patterns, and gga-miR-19a inhibitor repressed the expression of NF-κB, MyD88, and TNF-α, but enhanced the expression of ZMYND11. In conclusion, gga-miR-19a might suppress the expression of ZMYND11 in MG-infected chicken embryonic lungs and DF-1 cells, activate the NF-κB signaling pathway, and promote pro-inflammatory cytokines expression, the cell cycle progression and cell proliferation to defend against MG infection.

Gga-miR-101-3p Plays a Key Role in Mycoplasma gallisepticum (HS Strain) Infection of Chicken.

Mycoplasma gallisepticum (MG), one of the most pathogenic Mycoplasma, has caused tremendous economic loss in the poultry industry. Recently, increasing evidence has suggested that micro ribonucleic acids (miRNAs) are involved in microbial pathogenesis. However, little is known about potential roles of miRNAs in MG infection of chicken. In the present study, using miRNA Solexa sequencing we have found that gga-miR-101-3p was up-regulated in the lungs of MG-infected chicken embryos. Moreover, gga-miR-101-3p regulated expression of the host enhancer of zeste homolog 2 (EZH2) through binding to the 3’ un-translated region (3’-UTR) of EZH2 gene. Over-expression of gga-miR-101-3p significantly inhibited EZH2 expression and hence inhibited proliferation of chicken embryonic fibroblast (DF-1 cells) by blocking the G1-to-S phase transition. Similar results were obtained in MG-infected chicken embryos and DF-1 cells, where gga-miR-101-3p was significantly up-regulated, while EZH2 was significantly down-regulated. This study reveals that gga-miR-101-3p plays an important role in MG infection through regulation of EZH2 expression and provides a new insight into the mechanisms of MG pathogenesis.

Mycoplasma gallisepticum (HS strain) surface lipoprotein pMGA interacts with host apolipoprotein A-I during infection in chicken.

The adhesin protein from Mycoplasma gallisepticum (HS strain), namely pMGA1.2, is required for M. gallisepticum (MG) infection in chicken. However, the host factor(s) that interact with pMGA1.2 is not known. In this study, we prepared the membrane fraction of trachea epithelial cells from chicken embryos. Using an improved virus overlay protein blot assay (VOPBA) and glutathione S-transferase (GST) pull-down assay, we found that pMGA1.2 specifically bound to a ∼30kDa host protein. This host protein was further identified by mass spectrometry as chicken apolipoprotein A-I (ApoA-I). We expressed and purified the recombinant ApoA-I protein in Escherichia coli and confirmed that it bound to the purified pMGA1.2 protein in vitro. Transiently expressed pMGA1.2 and ApoA-I were colocalized in HeLa cells. Finally, we designed small interfering RNA (siRNA) molecules to knock down the expression of either ApoA-I or pMGA1.2, which inhibited the MG-induced cell cycle disruption in cells of chicken embryo fibroblast cell line (DF-1). Similarly, knockdown of ApoA-I inhibited the cilia loss and damage in chicken trachea cells in MG infection. In summary, ApoA-I may be an essential host factor in MG infection through interacting with pMGA1.2.

120 The prevalence of ticarcillin hypersusceptible Pseudomonas aeruginosa isolates from cystic fibrosis patients compared to non-cystic fibrosis patients

Background Ticarcillin, a carboxypenicillin, is rarely used to treat pulmonary infections in CF patients. A subpopulation of P. aeruginosa exists that is hypersusceptible to ticarcillin (Tic hs ) in vitro, (MIC ≥4 mg/ml). Aims To determine the prevalence of Tic hs in P. aeruginosa isolated from CF patients and to assess if this strain correlates with enhanced susceptibility to temocillin and other conventional antibiotics. We are correlating with clinical outcomes and associated VNTR type (work ongoing). Methods 23 isolates of P. aeruginosa from CF patients were compared to 18 non-CF P. aeruginosa isolates. MICs were determined by MicroBroth dilution and interpreted using EUCAST breakpoints. Results Resistant strains were more prevalent in the CF cohort compared to the non-CF cohort for all antibiotics except for ticarcillin and temocillin (Table 1). The prevalence of the Tic hs strain in our CF P. aeruginosa isolates was 48% compared to the non-CF Pseudomonas of 0%. The Tic hs strain was associated with reduced MICs to all antibiotics apart from gentamicin and ciprofloxacin (Table 2). Table 1MIC and percentage of resistant isolatesMeropenemCeftazidimeTicarcillinTemocillinCiprofloxacinGentamicinCFNo CFCFNo CFCFNo CFCFNo CFCFNo CFCFNo CFMIC R0.008–160.008–80.25–1282–160.125–12816–1280.5–128128–1280.03–160.03–41–640.25–4MIC 500.50.12544432412810.0621MIC 90411281612812812812840.125642%Res20%6%26%17%35%78%NANA60%7%30%0%%Sens80%94%74%83%65%22%NANA40%93%70%100%MIC R, MIC range; %Res, % resistant; % Sens, % Sensitive. Table 2Geometric mean MICs, Tic hs vs. Non Tic hs strainsMIC, geometric meanMeropenemCeftazidimeTicarcillinTemocillinCiprofloxacinGentamicinTic hs strain0.132.180.832.740.662.83Non Tic hs strain0.366.2339.4068.590.281.80 Conclusion Our data supports the existence of a Tic hs strain of P. aeruginosa in our CF patients. This appears to correlate with reduced MICs to temocillin to which P. aeruginosa would normally be resistant.

Comparative Genomics and Immunoinformatics Approach for the Identification of Vaccine Candidates for Enterohemorrhagic Escherichia coli O157:H7

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 strains are major human food-borne pathogens, responsible for bloody diarrhea and hemolytic-uremic syndrome worldwide. Thus far, there is no vaccine for humans against EHEC infections. In this study, a comparative genomics analysis was performed to identify EHEC-specific antigens useful as potential vaccines. The genes present in both EHEC EDL933 and Sakai strains but absent in nonpathogenic E. coli K-12 and HS strains were subjected to an in silico analysis to identify secreted or surface-expressed proteins. We obtained a total of 65 gene-encoding protein candidates, which were subjected to immunoinformatics analysis. Our criteria of selection aided in categorizing the candidates as high, medium, and low priority. Three members of each group were randomly selected and cloned into pVAX-1. Candidates were pooled accordingly to their priority group and tested for immunogenicity against EHEC O157:H7 using a murine model of gastrointestinal infection. The high-priority (HP) pool, containing genes encoding a Lom-like protein (pVAX-31), a putative pilin subunit (pVAX-12), and a fragment of the type III secretion structural protein EscC (pVAX-56.2), was able to induce the production of EHEC IgG and sIgA in sera and feces. HP candidate-immunized mice displayed elevated levels of Th2 cytokines and diminished cecum colonization after wild-type challenge. Individually tested HP vaccine candidates showed that pVAX-12 and pVAX-56.2 significantly induced Th2 cytokines and production of fecal EHEC sIgA, with pVAX-56.2 reducing EHEC cecum colonization. We describe here a bioinformatics approach able to identify novel vaccine candidates potentially useful for preventing EHEC O157:H7 infections.

Isolation and identification of Metarhizium anisopliae from Chilo venosatus (Lepidoptera: Pyralidae) cadaver

Sugarcane stem borer, Chilo venosatus Walker (Lepidoptera: Pyralidae) is a significant sugarcane pest in South China. Conidia or mycelia collected from the surface of sugarcane stem borer cadavers were cultured. The colony morphology, mycelia and conidial yield were observed with three-agar culture media: potato dextrose agar medium (PDA), potato dextrose with 1% (w/v) peptone agar medium (PPDA), and oatmeal agar medium (OMA). 16 different isolates were identified as Metarhizium anisopliae (Metschnikoff) based on macromorphological, micromorphological, and molecular characteristics, and PPDA was the better culture medium for vegetative growth and conidial yield (10 9 conidia/ml) than PDA (10 8 conidia/ml) and OMA (10 8 conidia/ml). To confirm whether these isolates were pathogenic to C. venosatus, their virulence to the sugarcane stem borer was tested in the laboratory. Both HS (10 isolates) and LY (6 isolates) strains were pathogenic to C. venosatus. Several highly virulent strains were screened in vitro (the mortalities of the eight isolates HS1, HS6, HS7, LY2, LY3, LY6, HS3 and HS9 were from 96 to 100%), and tests for controlling the sugarcane stem borer were preliminarily performed in vivo. The results show that significant (p=0.01) reductions in adult population were caused by the strains. So, M. anisopliae isolated from the cadavers of C. venosatus Walker is a potential biocontrol agent against this pest in South China.

Directed Evaluation of Enterotoxigenic Escherichia coli Autotransporter Proteins as Putative Vaccine Candidates

BackgroundEnterotoxigenic Escherichia coli (ETEC) is a major diarrheal pathogen in developing countries, where it accounts for millions of infections and hundreds of thousands of deaths annually. While vaccine development to prevent diarrheal illness due to ETEC is feasible, extensive effort is needed to identify conserved antigenic targets. Pathogenic Escherichia coli, including ETEC, use the autotransporter (AT) secretion mechanism to export virulence factors. AT proteins are comprised of a highly conserved carboxy terminal outer membrane beta barrel and a surface-exposed amino terminal passenger domain. Recent immunoproteomic studies suggesting that multiple autotransporter passenger domains are recognized during ETEC infection prompted the present studies.MethodologyAvailable ETEC genomes were examined to identify AT coding sequences present in pathogenic isolates, but not in the commensal E. coli HS strain. Passenger domains of the corresponding autotransporters were cloned and expressed as recombinant antigens, and the immune response to these proteins was then examined using convalescent sera from patients and experimentally infected mice.Principal FindingsPotential AT genes shared by ETEC strains, but absent in the E. coli commensal HS strain were identified. Recombinant passenger domains derived from autotransporters, including Ag43 and an AT designated pAT, were recognized by antibodies from mice following intestinal challenge with H10407, and both Ag43 and pAT were identified on the surface of ETEC by flow cytometry. Likewise, convalescent sera from patients with ETEC diarrhea recognized Ag43 and pAT, suggesting that these proteins are expressed during both experimental and naturally occurring ETEC infections and that they are immunogenic. Vaccination of mice with recombinant passenger domains from either pAT or Ag43 afforded protection against intestinal colonization with ETEC.ConclusionsPassenger domains of conserved autotransporter proteins could contribute to protective immune responses that develop following infection with ETEC, and these antigens consequently represent potential targets to explore in vaccine development.

Population Growth Potential of the Bed Bug, Cimex lectularius L.: A Life Table Analysis.

Experimental life tables were constructed and analyzed for three strains of the common bed bug: a pyrethroid-susceptible laboratory strain (HS), a highly resistant field strain (RR), and a field strain with a declining level of resistance (KR). Egg to adult survival in the RR strain was 94% compared with 79% and 69% in the HS and KR strains, respectively. The RR strain also developed significantly faster from egg to adult (∼35 days) than the other two strains (∼40 days). Analysis of a survivorship and fecundity life table for the RR strain produced the following results. The average life expectancy for a newly laid egg was ∼143 days, and that of a newly molted adult was ∼127 days. Females produced an average of 0.64 daughter eggs/day with the highest weekly production during the fifth week of adult life. Analysis of daily reproductive parity showed that females produced 1–3 and 4–6 eggs on 79 and 21% of the days, respectively, when egg laying occurred. The net reproductive rate (R0) of the RR strain was ∼35, which represents a 35-fold increase in the population per generation (∼92 days). The intrinsic rate of increase, r, was 0.054 indicating that the population multiplies 1.1 times/female/day (λ) and doubles in size every 13 days. The stable age distribution (cx) was dominated by nymphs (54%), followed by eggs (34%) and adults (12%). Reproductive values (vx) for the strain increased from egg to the adult stage.

Effect of Inorganic Phosphate on the Force and Number of Myosin Cross-Bridges During the Isometric Contraction of Permeabilized Muscle Fibers from Rabbit Psoas

The relation between the chemical and mechanical steps of the myosin-actin ATPase reaction that leads to generation of isometric force in fast skeletal muscle was investigated in demembranated fibers of rabbit psoas muscle by determining the effect of the concentration of inorganic phosphate (Pi) on the stiffness of the half-sarcomere (hs) during transient and steady-state conditions of the isometric contraction (temperature 12°C, sarcomere length 2.5μm). Changes in the hs strain were measured by imposing length steps or small 4kHz oscillations on the fibers in control solution (without added Pi) and in solution with 3–20mM added Pi. At the plateau of the isometric contraction in control solution, the hs stiffness is 22.8±1.1 kPa nm−1. Taking the filament compliance into account, the total stiffness of the array of myosin cross-bridges in the hs (e) is 40.7±3.7 kPa nm−1. An increase in [Pi] decreases the stiffness of the cross-bridge array in proportion to the isometric force, indicating that the force of the cross-bridge remains constant independently of [Pi]. The rate constant of isometric force development after a period of unloaded shortening (rF) is 23.5±1.0s−1 in control solution and increases monotonically with [Pi], attaining a maximum value of 48.6±0.9s−1 at 20mM [Pi], in agreement with the idea that Pi release is a relatively fast step after force generation by the myosin cross-bridge. During isometric force development at any [Pi], e and thus the number of attached cross-bridges increase in proportion to the force, indicating that, independently of the speed of the process that leads to myosin attachment to actin, there is no significant (>1ms) delay between generation of stiffness and generation of force by the cross-bridges.

Cocaethylene-induced kindling of seizure effects: Cross-specificity with cocaine

Sensitization and cross-sensitization to the seizurogenic effects of cocaine and cocaethylene were examined in the HS strain of mice. Animals were administered IP injections of either 48 mg/kg cocaine or 32 mg/kg cocaethylene once per day for 4 days. On the fifth day, mice were injected with either the same drug that was administered on days 1–4 or the alternative psychostimulant and the occurrence of seizure activity was recorded. Repeated cocaine administration resulted in the induction of tonic-clonic seizures and status epilepticus in 90% of the animals tested with cocaine on the fifth day. A similar increase in seizure prevalence, noted as a kindling effect, was observed in cocaethylene-treated animals tested with cocaethylene in that 90% of the mice exhibited status epilepticus on the last test day. Significant cross-sensitization was observed only in the group that received cocaethylene following repeated cocaine exposure. However, data obtained from animals injected with cocaine following cocaethylene treatment also were suggestive of cross-sensitization effects. Results are discussed in terms of the potential mechanistic differences between cocaine and its ethanol-derived product, as well as its relevance to cocaine use/abuse.

Premorbid behaviors produced by cocaine, ethanol and cocaethylene in the mouse

1. 1. The premorbid behaviors produced by the administration of cocaine, ethanol, their combination, as well as a metabolite produced by their co-administration, viz. cocaethylene, were defined, determined and quantified in the HS strain of mice. 2. 2. The LD 50 for ethanol was 9.71 g/kg in males and 9.45 g/kg in females, whereas the LD 50 values in male and female mice for cocaine were 101.55 and 90.00 mg/kg, respectively. 3. 3. The data indicate that clonic-tonic seizures continued into status epilepticus after cocaine administration and prior to cocaine-induced lethality. In contrast, administration of the cocaine-ethanol metabolite cocaethylene produced status epilepticus without producing clonic-tonic seizures yet still resulted in lethality. 4. 4. Thus, both cocaine and cocaethylene may produce their lethal effects in mice through neuro-regulatory mechanisms mediating protracted seizure induction.

A reexamination of the genetic control of sonic vocalization in mice.

Sonic vocalizations in response to handling were studied in the parent inbreds of a random-bred heterogeneous stock (HS/Ibg). Results of a backcross of vocalizing and nonvocalizing HS to C57BL/6 were roughly consistent with Whitney's single dominant gene hypothesis, but an unexpected age effect was found. F1 crosses of IS/Bi, the postulated vocalization gene donor, demonstrated a recessive mode of inheritance rather than dominance with 50% penetrance which had been predicted. The previously untested inbred parent strains RIII and AKR proved to be intermediate and high vocalizers, respectively. Mode of inheritance in crosses involving AKR was significantly different in crosses to the different low-vocalizing lines. It is suggested that if a major gene accounts for most of the variation in vocalization in response to handling in the HS strain, the AKR strain is the most likely donor.

Protein Electrophoretic Pattern of Two Chlorella Mutants with Low and High Content of Sulphur‐Amino Acids

AbstractTwo mutants of Chlorella vulgaris characterized by high (HS) or low (LS) content of sulphur‐amino acids were compared to the wild strain with respect to their protein electrophoretic pattern.Three new bands, not present in the LS and wild strains, were found in the HS mutant. In algae grown in the presence of 35S labelled sulphate two of these new bands showed a very high 35S specific activity. Some electrophoretic bands common to LS, HS, and wild strain, were present in different proportions and showed different levels of specific radioactivity for each strain. Therefore, mutational events appear to have affected both the amino acid composition of single proteins and the relative amount of proteins with high and low sulphate content.

Some Immunochemical Properties of Dextransucrase and Invertase from Streptococcus mutans

Dextransucrase and invertase of some strains of Streptococcus mutans were examined by immunodiffusion with antisera against enzymes purified from strain HS-6 (Bratthall's serotype a). Both antisera cross-reacted with crude enzyme preparations from the other serotype a (strains HS-1 and AHT) and d organisms (strains KIR, OMZ176, and OMZ65) but not with those from serotype b (strains FA-1 and BHT) or c organisms (strains GS-5, Ingbritt, and NCTC 10449). Based upon the antiserum used, the orders of antigenic similarity of the cross-reacting enzymes to the HS-6 enzymes were HS-6 > HS-1 > AHT = KIR = OMZ176 = OMZ65 for dextransucrase and HS-6 = HS-1 > AHT = KIR = OMZ176 = OMZ65 for invertase. It was found that the enzymes from serotype a organisms were not always antigenically homogeneous, as seen between strains HS-6, HS-1, or AHT for dextransucrase, and between the HS group and strain AHT for invertase. Antiserum against the HS-6 dextransucrase markedly inhibited the heterologous dextransucrases of serotype a organisms with the exception of strain HS-1 and d organisms, with or without the addition of dextran.

Warfarin resistance and vitamin K requirement in the rat.

The development of vitamin K deficiency, vitamin K requirement and warfarin susceptibility were studied in several types of warfarin-resistant and non-resistant rat. Domesticated HW strain rats needed about 13 times as much vitamin K1 as did Wistar rats to maintain normal blood-clotting function, while HS strain rats were intermediate in this and in their susceptibility to warfarin. The vitamin K requirement of Wistar hybrids resembled that of the Wistar parent or was intermediate. Hypoprothrom-binaemia was induced at least as readily in non-resistant wild rats as in HS rats. A new diet suitable for inducing vitamin K deficiency in conventionally maintained Wistar rats is described, and it is suggested that the HW strain could be used for vitamin K bioassay. The genetical basis of warfarin resistance is discussed.

Histocompatibility antigens in the rat: the AS2 strain in relation to the AS, BS and HS strains.

SummaryThe origin of the inbred albino rat strain AS2 is described. With the exception of weak male → female incompatibility, the strain appears to be isohistogenic and homozygous at all loci determining histocompatibility antigens. The weak antigen distinguishing males from otherwise isohistogenic females is identical in the AS2 and HS strains. The AS2 strain possesses at least one histocompatibility antigen in common with each of strains AS, BS and HS. The AS. BS and HS strains possess identical alleles at a major histocompatibility locus at which they differ from the AS2 strain. Donor‐host disparity at this locus regularly leads to the development of local graft versus host reactions following the injection of 50 × 106 normal parental strain spleen cells beneath the renal capsule of F1 hybrids. Where donor and host are compatible at this locus, despite disparity at up to 3 other loci determining strong antigens, local graft versus host reactions do not occur following normal spleen cell transfer, although they occur somewhat irregularly if specifically sensitised spleen donors are used. It therefore seems likely that this major locus is the Ag‐B locus. Mean skin graft survival times are only slightly shorter in Ag‐B incompatible combinations than in those combinations which are compatible at Ag‐B hut differ in respect of other strong histocompatibility antigens. Parental strain → F2 hybrid skin grafts show the closely related AS and AS2 strains to differ from each other at an estimated 4‐5 histocompatibility loci, one of which is the Ag‐B locus.

Relation between Multiplication Rate and Temperature in Tetrahymena pyriformis, Strains HS and GL

SUMMARY. The multiplication rate of Tetrahymena pyriformis HS in proteose peptone medium was measured at 12 temperatures between 18.4°C. and 36.6°C. At the temperature optimum, 32.5°C., the generation time is 2.25 hours. The upper lethal temperature lies between 36.6°C. and 38.0°C. Similarly, a study of Tetrahymena pyriformis GL revealed a temperature optimum for multiplication of 29°C. with a generation time of 3.70 hours. The upper lethal temperature falls between 34.6°C. and 35.4°C. At all temperatures employed the HS strain of organisms multiplies more rapidly than strain GL. Under identical conditions, the two strains have distinctly different growth optima, upper lethal temperatures and growth rates.As measured by multiplication rate the readjustment to a sudden change in temperature (from 18.4°C. to 27.7°C.) is completed very rapidly, with an effective lag time of about 1 hour. Such a shift in temperature gives rise to a small degree of division synchrony during the first and second population doublings which follow. Subsequently, all traces of division synchrony are lost.