Synthesis of nucleic acid and protein in L cells infected with the agent of meningopneumonitis

Division without Binary Fission: Cell Division in the FtsZ-Less Chlamydia

Chlamydia is an obligate intracellular bacterial pathogen that has significantly reduced its genome size in adapting to its intracellular niche. Among the genes that Chlamydia has eliminated is ftsZ, encoding the central organizer of cell division that directs cell wall synthesis in the division septum. These Gram-negative pathogens have cell envelopes that lack peptidoglycan (PG), yet they use PG for cell division purposes. Recent research into chlamydial PG synthesis, components of the chlamydial divisome, and the mechanism of chlamydial division have significantly advanced our understanding of these processes in a unique and important pathogen. For example, it has been definitively confirmed that chlamydiae synthesize a canonical PG structure during cell division. Various studies have suggested and provided evidence that Chlamydia uses MreB to substitute for FtsZ in organizing and coordinating the divisome during division, components of which have been identified and characterized. Finally, as opposed to using an FtsZ-dependent binary fission process, Chlamydia employs an MreB-dependent polarized budding process to divide. A brief historical context for these key advances is presented along with a discussion of the current state of knowledge of chlamydial cell division.

Computational Methods for Mapping, Assembly and Quantification for Coding and Non-coding Transcripts

The measurement of gene expression has long provided significant insight into biological functions. The development of high-throughput short-read sequencing technology has revealed transcriptional complexity at an unprecedented scale, and informed almost all areas of biology. However, as researchers have sought to gather more insights from the data, these new technologies have also increased the computational analysis burden. In this review, we describe typical computational pipelines for RNA-Seq analysis and discuss their strengths and weaknesses for the assembly, quantification and analysis of coding and non-coding RNAs. We also discuss the assembly of transposable elements into transcripts, and the difficulty these repetitive elements pose. In summary, RNA-Seq is a powerful technology that is likely to remain a key asset in the biologist's toolkit.

Inhibition of Deoxyribonucleic Acid Synthesis in Synchronized Populations of L Cells Infected with Chlamydia psittaci

Infection of L cells with Chlamydia psittaci inhibited the burst of deoxyribonucleic acid synthesis that occurs when the host cells are released from a double thymidine block.

Cell Wall Synthesis by Chlamydia psittaci Growing in L Cells

Biochemical events accompanying changes in structure and behavior of the cell walls of Chlamydia psittaci strain 6BC during its developmental cycle in L cells (mouse fibroblasts) were studied by measuring at short intervals the effect of d-cycloserine and penicillin G on incorporation of labeled intermediates into acid-insoluble fractions of infected L cells in which host incorporation had been inhibited by cycloheximide and into intact chlamydial cells and cell walls separated from the infected L cells. d-Cycloserine enhanced the incorporation of (14)C-l-alanine at all times in the developmental cycle, but the incorporation of (14)C-l-lysine was always inhibited. In parallel experiments, penicillin G had no effect on incorporation of any of these intermediates, but when infected L cells incorporated (14)C-l-alanine in the presence of penicillin G, the labeled alanine was released more rapidly in the subsequent absence of the antibiotic than in its continued presence. When either penicillin G or d-cycloserine was present throughout the developmental cycle, C. psittaci continued to synthesize deoxyribonucleic acid and protein, but at less than normal rates.

Interaction of chlamydiae and host cells in vitro

The obligately intracellular bacteria of the genus Chlamydia, which is only remotely related to other eubacterial genera, cause many diseases of humans, nonhuman mammals, and birds. Interaction of chlamydiae with host cells in vitro has been studied as a model of infection in natural hosts and as an example of the adaptation of an organism to an unusual environment, the inside of another living cell. Among the novel adaptations made by chlamydiae have been the substitution of disulfide-bond-cross-linked polypeptides for peptidoglycans and the use of host-generated nucleotide triphosphates as sources of metabolic energy. The effect of contact between chlamydiae and host cells in culture varies from no effect at all to rapid destruction of either chlamydiae or host cells. When successful infection occurs, it is usually followed by production of large numbers of progeny and destruction of host cells. However, host cells containing chlamydiae sometimes continue to divide, with or without overt signs of infection, and chlamydiae may persist indefinitely in cell cultures. Some of the many factors that influence the outcome of chlamydia-host cell interaction are kind of chlamydiae, kind of host cells, mode of chlamydial entry, nutritional adequacy of the culture medium, presence of antimicrobial agents, and presence of immune cells and soluble immune factors. General characteristics of chlamydial multiplication in cells of their natural hosts are reproduced in established cell lines, but reproduction in vitro of the subtle differences in chlamydial behavior responsible for the individuality of the different chlamydial diseases will require better in vitro models.

Characterization and identification of early proteins in Chlamydia trachomatis serovar L2 by two-dimensional gel electrophoresis

The synthesis of early proteins from Chlamydia trachomatis serovar L2 was analyzed by two-dimensional gel electrophoresis. By pulse-label experiments, the synthesis of seven proteins was observed at 2 to 8 h postinfection before the major outer membrane protein was detected at 8 to 10 h after infection. The early proteins were synthesized throughout the 30-h period investigated, but the synthesis of three proteins of 75, 62, and 45 kilodaltons decreased from 26 to 30 h postinfection. Pulse-chase analysis showed that the signals from the same three proteins declined 26 to 30 h after infection. Three of the early proteins were identified as the S1 ribosomal protein, the GroEL-like protein, and DnaK-like protein, respectively.

Deoxyribonucleic acid synthesis, cell cycle progression, and division of Chlamydia-infected HeLa 229 cells

The fate of lymphogranuloma venereum strain Chlamydia-infected HeLa 229 cells was examined by determining the rate of deoxyribonucleic acid synthesis and the kinetics of entry into and progression through S phase and by time-lapse cinemicrography. At an input multiplicity of 5 or less, Chlamydia-infected cells showed no inhibition of host deoxyribonucleic acid synthesis or cell cycle progression. Cinemicrography showed division of inclusion-containing cells, with one or both daughters receiving chlamydial inclusions. Analysis of the family trees indicated that the generation times of infected HeLa 229 were not altered relative to those of the uninfected cells.

The chlamydia: molecular biology of procaryotic obligate parasites of eucaryocytes

Images

Division of single host cells after infection with chlamydiae

Mouse fibroblasts (L cells) were infected in suspension with Chlamydia psittaci (6BC) and then plated out on a solid substrate at a density of 80 cells per cm2 so that the effect of chlamydial infection on the division of single host cells and their progeny could be determined. Uninfected L cells multiplied with a mean generation time of 15 h. The generation time of single L cells infected with 1.5 50% infectious units (ID50) of C. psittaci was over twice as long. Half of the infected L cells had divided once by day 4 after infection, and the rest had divided more than once. Division of infected cells frequently produced one infected and one uninfected daughter. About half of the L cells infected with 15 ID50 of C. psittaci divided at least once before most of them detached from their substrate before observation on day 3. Less than 10% of the L cells infected with 75 ID50 of C. psittaci divided before they were lost from their substrate by day 2. Comparable results were obtained with single L cells infected with a lymphogranuloma venereum (440L) strain of C. trachomatis and with single HeLa 229 cells infected with C. psittaci. It was concluded that high multiplicities of infection of host cells with chlamydiae quickly bring cell division to a halt, whereas lower multiplicities slow but do not immediately stop the division of host cells. However, indefinitely multiplying clones of chlamydia-infected host cells were not observed. The method used here should be applicable to other studies on the division of cells in culture.

Toxicity of low and moderate multiplicities of Chlamydia psittaci for mouse fibroblasts (L cells)

When mouse fibroblasts (L cells) were infected in suspension or in monolayer with 10 to 100 50% infectious doses (ID(50)) of Chlamydia psittaci (6BC) per host cell, they showed signs of damage 24 to 48 h later. Host-cell injuries were termed multiplication dependent when both the ingestion and subsequent reproduction of C. psittaci were required; when only ingestion but not replication was needed, the injuries were considered to be multiplication independent. The time that the injury was first apparent, as well as its final magnitude, was proportional to the multiplicity of infection. When L cells ingested infectious or ultraviolet-inactivated C. psittaci, damage was manifested by failure to exclude trypan blue, by leakage of lactic dehydrogenase, by inhibition of reproduction as measured by ability to form colonies, by inhibition of protein and deoxyribonucleic acid synthesis, and eventually by cell disintegration. Infectious, but not ultraviolet-killed, chlamydiae stimulated host-cell glycolysis. Heat-killed chlamydiae were without measurable toxicity. The time of appearance of host-cell injury was always earlier, and its terminal magnitude always greater, with infectious inocula than with ultraviolet-inactivated ones. The multiplication-independent toxicity of ultraviolet-killed C. psittaci disappeared with inocula of less than 10 ID(50) per L cell, but an inoculum of only a single ID(50) of infectious chlamydiae per host cell injured most of the cells it infected, as evidenced by increased trypan blue staining and decreased efficiency of colony formation. The toxicity of multiplicities of infection between 10 and 100 ID(50) of infectious C. psittaci per host cell was the sum of both multiplication-dependent and -independent components. The effects of chloramphenicol and isoleucine deficiency on the ability of C. psittaci to injure L cells suggested that some synthesis of protein by both parasite and host may be essential for expression of multiplication-independent chlamydial toxicity. The failure of infectious chlamydiae to stimulate host-cell glycolysis in the presence of cycloheximide suggested that this multiplication-dependent consequence of chlamydial infection was also dependent on protein synthesis by the host.

Requirements for ingestion of Chlamydia psittaci by mouse fibroblasts (L cells)

Ingestion of 14C-amino acid-labeled Chlamydia psittaci (6BC) by mouse fibroblasts (L cells) was inhibited when the host cells were incubated for 30 min at 37 degrees C in Earle salts containing 10 mug of crystalline trypsin per ml. Tryptic digestion also inhibited the ingestion of 1-mum polystrene latex beads. Trypsin-treated L cells almost completely recovered their ability to ingest chlamydiae after 4 h at 37 degrees C in medium 199 with 5% fetal calf serum. Cycloheximide (10 mug/ml) blocked this recovery. Heating 14C-amino acid-labeled C. psittaci for 3 min at 60 degrees C inhibited its ingestion by L cells, whereas inactivating it with ultraviolet light was without effect on the ingestion rate. These results show that efficient ingestion of C. psittaci by L cells involves trypsin-labile sites on the host and heat-sensitive sites on the parasite. The failure of excess unlabeled infectious C. psittaci to promote the ingestion of 14C-labeled heat-inactivated chlamydiae suggests that direct interaction between these two sites must occur for uptake to proceed normally.

Ultrastructural cytochemical evidence for the activation of lysosomes in the cytocidal effect of Chlamydia psittaci

The cytopathic effect of the polyarthritis strain of Chlamydia psittaci was studied in cultured bovine fetal spleen cells and found to be mediated by the release of lysosomal enzymes into the host cytoplasm during the late stages of chlamydial development. Ultrastructural cytochemical analysis and cell fractionation studies of infected cells revealed a close relationship between the stage of chlamydial development, fine structural features of the host, and localization of lysosomal enzyme activities. After adsorption, chlamydiae entered the host cells by endocytosis. The endocytic vacuoles containing individual chlamydiae and later the inclusion vacuoles containing the different chlamydial developmental forms were always free from lysosomal enzyme activity. Even after extensive multiplication of chlamydiae, lysosomal enzymes remained localized within lysosomes or their precursors in the host cell. Coincident with the process of chlamydial maturation, lysosomal enzymes were released into the host cytoplasm and were always associated with disintegration of host cell constituents and lysis. The chlamydiae appeared to be protected from this lysosomal enzyme activity by the inclusion membrane. After release from the inclusion, elementary bodies maintained their fine structural features, whereas all other chlamydial developmental forms lost their ultrasturctural integrity.

Formation and destruction of internal membranes in L cells infected with Chlamydia psittaci

L cells (mouse fibroblasts), uninfected and infected with Chlamydia psittaci (meningopneumonitis strain), were labeled with (14)C-amino acids, and their membranous organelles were separated by isopycnic equilibrium centrifugation of whole cell homogenates on discontinuous sucrose density gradients. Incorporation of labeled amino acids into host and parasitic proteins was differentiated on the basis of susceptibility to cycloheximide. Twenty hours after infection with C. psittaci, incorporation of newly synthesized proteins into the internal membranes of L cells was almost completely inhibited, and internal membranes made prior to infection were altered or destroyed. The unit membrane that at all times surrounds the cytoplasmic vacuole containing the multiplying chlamydiae was made by the host from membranes or membrane precursors present before infection. No proteins synthesized by C. psittaci became associated with host cell membranes. Destruction or modification of the internal membranes of the host cell may be an integral part of the chlamydial developmental cycle.

Interaction of L cells and Chlamydia psittaci: entry of the parasite and host responses to its development

The entry and development of Chlamydia psittaci in the L cell was studied by using purified, infectious parasites at high multiplicity. Entry of the parasite was accomplished by an act of phagocytosis by the host which was independent of an adsorption stage but was temperature-dependent. Kinetic studies of phagocytosis performed with (14)C-amino acid-labeled, purified parasites indicated that the rate of phagocytosis was directly proportional to the multiplicity of inoculation. Electron microscopy of cells infected at high multiplicity with purified infectious C. psittaci showed that phagocytosed chlamydiae were segregated in a host phagocytic vacuole throughout their developmental cycle which consisted of the transition of infecting elementary bodies to reticulate bodies dividing by binary fission, followed by the reemergence of a population of elementary bodies. The process of the transition was examined and a proposed sequence of intermediate bodies is presented. In isopycnic gradients of fractionated, infected L cells, chlamydial phagocytic vacuoles were apparent as a dense band distinct from lysosome and mitochondrion peaks, as indicated by acid phosphatase and cytochrome oxidase activities. Chlamydiae inactivated by heat or neutralized by antiserum were phagocytosed and appeared in lysosomes within 12 hr after infection according to electron microscopy; however, chlamydiae which were continuously inhibited in their development by chloramphenicol were retained intact in the cell for 24 hr without lysosomal response. The possibility of a lysosomal inhibitor on the native parasite is discussed.

Effect of ionizing irradiation on susceptibility of McCoy cell cultures to Chlamydia trachomatis

The effect of graded doses of irradiation (cobalt-60) on the morphology of McCoy cells was analyzed, and 4,000 to 5,000 r was selected as a satisfactory dose for production of giant cells. The susceptibility of radiation-induced giant cells to chlamydial infection was compared with that of nonirradiated cells by using three strains of Chlamydia trachomatis and one of C. psittaci. Monolayers of giant cells were more susceptible than normal McCoy cells as indicated by (i) greater numbers of inclusions (four- to eightfold) per unit area of monolayer, (ii) larger inclusions (fourfold greater in area), (iii) higher infective titers (1 log or more greater) of harvested cells, and (iv) greater ease of promoting a second cycle of growth. Graded doses of irradiation were applied also to mouse fibroblast (L) cells, and a similar increase in susceptibility to chlamydial infection was noted. It is concluded that giant cells produced by irradiation possess advantages over nonirradiated cells in culture for growth of Chlamydia.

Effect of infection with the meningopneumonitis agent on deoxyribonucleic acid and protein synthesis by its L-cell host

Cycloheximide, which had already been shown to inhibit protein synthesis in Earle's L cells (mouse fibroblasts) without having any effect on the multiplication or protein synthesis in Chlamydia psittaci (strain meningopneumonitis) infecting these host cells, also caused greater than 90% inhibition of deoxyribonucleic acid (DNA) synthesis in L cells after a 3-hr exposure to the drug. L cells infected with the meningopneumonitis agent and treated with cycloheximide were used to follow meningopneumonitis-specific DNA synthesis during intracellular growth of the parasite. The rate at which labeled precursors were incorporated into parasite DNA doubled every 2 hr. The effect of meningopneumonitis infection on L-cell DNA and protein synthesis was investigated in logarithmically growing and in stationary-phase (nondividing) populations of L cells. Host-specific DNA and protein synthesis appeared to be inhibited in infected L cells when compared with logarithmically growing control cells, whereas no inhibition was apparent when the comparison was made with stationary-phase control cells. The maximal amount of protein and DNA synthesis that occurred in meningopneumonitis-infected L cells was equal to the amount of DNA and protein synthesized in logarithmically growing, uninfected L cells. A possible explanation of these results is given.

Stability of the nucleic acids of L cells after infection with the meningopneumonitis agent

The stability of host nucleic acids in L cells infected with Chlamydia psittaci (strain meningopneumonitis) was studied. The L cells were prelabeled with either (32)P-orthophosphate, (3)H-uridine, or (3)H-thymidine. After infection, the redistribution of each label among the different fractions of host and parasite was quantitatively determined and compared. There were no signs of accelerated degradation of host nucleic acid as the consequence of meningopneumonitis infection. Comparison of the specific activities of the meningopneumonitis nucleic acids with that of the acid-soluble fraction of host cell cytoplasm suggested that the major source of precursors for parasite nucleic acid synthesis was the common cytoplasmic pool of the infected host cell.

Inhibition of thymidine kinase activity and deoxyribonucleic acid synthesis in L cells infected with the meningopneumonitis agent

The activities of enzymes related to deoxyribonucleic acid (DNA) synthesis were studied in uninfected L cells and in L cells infected with Chlamydia psittaci (strain meningopneumonitis). The meningopneumonitis agent multiplied normally but failed to induce the synthesis of thymidine kinase in LM (TK(-)) cells which contain no thymidine kinase in the uninfected state. It was concluded that this microorganism has no thymidine kinase of its own and that it does not depend on the functioning of the host enzyme for synthesizing its DNA. Exposure of clone 5b L cells to the meningopneumonitis agent was followed by a decline in their thymidine kinase activity to nearly zero levels, whereas the levels of uridine kinase and thymidylate synthetase remained unchanged. Inhibition of thymidine kinase activity in L cells occurred soon after infection and required new protein synthesis by the meningopneumonitis agent. This inhibition occurred before inhibition of host DNA synthesis, but it was not an essential prelude to the latter inhibition. On the basis of this and previous investigations and in light of present knowledge of the mammalian cell cycle, it was postulated that the meningopneumonitis agent inhibits macromolecular synthesis in L cells by preventing the initiation of a new cell cycle.

Biosynthesis of arginine in L cells infected with chlamydiae

Three members of the genus Chlamydia were examined for their ability to synthesize arginine, an ability their L cell (mouse fibroblasts) hosts lacked. C. psittaci (strain 6BC) multiplied in arginine-free medium 199 without significant decrease in titer and incroporated (14)C-glutamate and (14)C-ornithine into the arginine fraction of its protein. In arginine-free media, C. trachomatis (strain mouse pneumonitis) and C. psittaci (strain meningopneumonitis) grew to only 1 to 10% of the titer obtained in arginine-containing media. The decreased ability of these two strains to multiply in arginine-free media was paralleled by a decreased ability of infected host cells to incorporate (14)C-glutamate into protein arginine. These results suggest that chlamydiae either synthesize arginine themselves, or, in some unknown manner, cause their host cells to do so.

Separation of protein synthesis in meningopneumonitisgent from that in L cells by differential susceptibility to cycloheximide

Cycloheximide had no effect on multiplication of the meningopneumonitis agent in L cells in concentrations which eliminated over 90% of the protein synthesis in the host cells. Infected L cells treated with cycloheximide, however, incorporated labeled amino acids into the trichloroacetic acid-insoluble fraction. This incorporation was attributed to the biosynthetic activity of the meningopneumonitis agent. Synthesis of meningopneumonitis protein was abolished by chloramphenicol and chlortetracycline, inhibitors of bacterial protein synthesis, at concentrations which did not inhibit protein synthesis in L cells. Protein synthesis in the meningopneumonitis agent was sustained at a high rate when the host cells remained viable and declined as the L cells died. Overall host protein synthesis was not inhibited by multiplication of the meningopneumonitis agent.

Use of tetrazolium salts for electron transport studies in meningopneumonitis. 3. Separation and examination of large and small particles

Purified suspensions of meningopneumonitis can be separated on potassium tartrate gradient into populations which are 80 to 90% large particles and those which are 90% small particles. Examination of the tetrazole reduction of both particle types indicates that the small particle has associated with it all of the enzymatic activity of the preparation; it also has associated with it most of the infectivity as well.

Autoradiographic study of deoxyribonucleic acid synthesis in L cells infected with the agent of meningopneumonitis

Moore, Dorothy E. (University of Chicago, Chicago, Ill.), and James W. Moulder. Autoradiographic study of deoxyribonucleic acid synthesis in L cells infected with the agent of meningopneumonitis. J. Bacteriol. 92:1128-1132. 1966.-L cells infected with the agent of meningopneumonitis were labeled with H(3)-cytidine at 5-hr intervals after infection, and cell samples were fixed every 5 hr after labeling. These preparations were then digested with ribonuclease, stained by the Feulgen procedure, and examined by autoradiography. Labeled meningopneumonitis inclusions were first seen 15 hr after infection. Deoxyribonucleic acid (DNA) was synthesized in both L-cell nuclei and meningopneumonitis agent for as long as 40 hr after infection. Nuclear DNA synthesis was unaffected until 25 hr after infection, at which time synthesis of agent DNA reached its peak. After 25 hr, both meningopneumonitis and L cell DNA synthesis declined.

Availability of bases and nucleosides as precursors of nucleic acids in L cells and in the agent of meningopneumonitis

Tribby, Ilse I. E. (University of Chicago, Chicago, Ill.), and James W. Moulder. Availability of bases and nucleosides as precursors of nucleic acids in L cells and in the agent of meningopneumonitis. J. Bacteriol. 91:2362-2367. 1966.-Uninfected L cells and the meningopneumonitis agent propagated in L cells utilized exogenous adenine, guanine, and their ribonucleosides and deoxyribonucleosides for synthesis of both deoxyribonucleic acid (DNA) and ribonucleic acid. Cytosine, cytidine, and uridine were also incorporated into the nucleic acids of both host and parasite. L cells and the meningopneumonitis agent incorporated uracil, thymine, and deoxyuridine very poorly. L cells utilized thymidine and deoxycytidine almost exclusively for DNA synthesis, but the meningopneumonitis agent did not incorporate these nucleosides at all. Since the L cell had previously been shown to convert added thymidine to its nucleotides, mainly the triphosphate, it was concluded that the meningopneumonitis agent can utilize neither the thymidine nor the thymidine nucleotides of the L-cell pool, and that it can probably synthesize the thymidine triphosphate needed for DNA synthesis from the uridine of the L-cell pool.