Early effects of Bdellovibrio infection on the syntheses of protein and RNA of host bacteria

Bdellovibrio bacteriovorus directly attacks Pseudomonas aeruginosa and Staphylococcus aureus Cystic fibrosis isolates

Bdellovibrio bacteriovorus is a predator bacterial species found in the environment and within the human gut, able to attack Gram-negative prey. Cystic fibrosis (CF) is a genetic disease which usually presents lung colonization by Pseudomonas aeruginosa or Staphylococcus aureus biofilms. Here, we investigated the predatory behavior of B. bacteriovorus against these two pathogenic species with: (1) broth culture; (2) "static" biofilms; (3) field emission scanning electron microscope (FESEM); (4) "flow" biofilms; (5) zymographic technique. We had the first evidence of B. bacteriovorus survival with a Gram-positive prey, revealing a direct cell-to-cell contact with S. aureus and a new "epibiotic" foraging strategy imaged with FESEM. Mean attaching time of HD100 to S. aureus cells was 185 s, while "static" and "flow" S. aureus biofilms were reduced by 74 (at 24 h) and 46% (at 20 h), respectively. Furthermore, zymograms showed a differential bacteriolytic activity exerted by the B. bacteriovorus lysates on P. aeruginosa and S. aureus. The dual foraging system against Gram-negative (periplasmic) and Gram-positive (epibiotic) prey could suggest the use of B. bacteriovorus as a "living antibiotic" in CF, even if further studies are required to simulate its in vivo predatory behavior.

Shedding light on microbial predator-prey population dynamics using a quantitative bioluminescence assay

This study assessed the dynamics of predation by Bdellovibrio bacteriovorus HD 100. Predation tests with two different bioluminescent strains of Escherichia coli, one expressing a heat-labile bacterial luciferase and the other a heat-stable form, showed near identical losses from both, indicating that protein expression and stability are not responsible for the "shutting-off" of the prey bioluminescence (BL). Furthermore, it was found that the loss in the prey BL was not proportional with the predator-to-prey ratio (PPR), with significantly greater losses seen as this value was increased. This suggests that other factors also play a role in lowering the prey BL. The loss in BL, however, was very consistent within nine independent experiments to the point that we were able to reliably estimate the predator numbers within only 1 h when present at a PPR of 6 or higher, Using a fluorescent prey, we found that premature lysis of the prey occurs at a significant level and was more prominent as the PPR ratio increased. Based upon the supernatant fluorescent signal, even a relatively low PPR of 10-20 led to approximately 5% of the prey population being prematurely lysed within 1 h, while a PPR of 90 led to nearly 15% lysis. Consequently, we developed a modified Lotka-Volterra predator-prey model that accounted for this lysis and is able to reliably estimate the prey and bdelloplast populations for a wide range of PPRs.

Combined application of bacterial predation and carbon dioxide aerosols to effectively remove biofilms

This study evaluated predation with Bdellovibrio bacteriovorous and CO(2) aerosol spraying to remove fluorescent Escherichia coli biofilms from silicon chips. Initial tests found that 7.5×10(5) viable E. coli cells were dispersed into the surrounding environment during aerosol treatment. The total number dispersed per test decreased to only 16 for predated biofilms. This is nearly 50,000-fold lower compared to untreated chips and 1000-fold lower compared to chips soaked in HEPES buffer only. Both scanning electron microscopy (SEM) and fluorescent microscopy analyses confirmed that predation alone did not completely eradicate the biofilm population. When used in conjunction with CO(2) aerosols, however, no fluorescent signals remained and the SEM pictures showed a pristine surface devoid of bacteria. Consequently, this study demonstrates these two methods can be used with each other to significantly remove biofilms from surfaces while also significantly reducing the likelihood of human exposure to potential pathogens during their removal.

A transcriptional "Scream" early response of E. coli prey to predatory invasion by Bdellovibrio

We have transcriptionally profiled the genes differentially expressed in E. coli prey cells when predatorily attacked by Bdellovibrio bacteriovorus just prior to prey cell killing. This is a brief, approximately 20–25 min period when the prey cell is still alive but contains a Bdellovibrio cell in its periplasm or attached to and penetrating its outer membrane. Total RNA was harvested and labelled 15 min after initiating a semi-synchronous infection with an excess of Bdellovibrio preying upon E. coli and hybridised to a macroarray spotted with all predicted ORFs of E. coli. SAM analysis and t-tests were performed on the resulting data and 126 E. coli genes were found to be significantly differentially regulated by the prey upon attack by Bdellovibrio. The results were confirmed by QRT-PCR. Amongst the prey genes upregulated were a variety of general stress response genes, potentially “selfish” genes within or near prophages and transposable elements, and genes responding to damage in the periplasm and osmotic stress. Essentially, the presence of the invading Bdellovibrio and the resulting damage to the prey cell elicited a small “transcriptional scream”, but seemingly no specific defensive mechanism with which to counter the Bdellovibrio attack. This supports other studies which do not find Bdellovibrio resistance responses in prey, and bodes well for its use as a “living antibiotic”.

Protein uptake into E. coli during Bdellovibrio infection. A process of reverse secretion?

Bdellovibrio bacteriovorus is a small bacterial parasite that infects other Gram-negative bacteria, resides in the periplasm of the host cell, and utilizes host macromolecules as a source of nutrients. Evidence is summarized suggesting that B. bacteriovorus secretes proteases and nucleases synthesized in its own cytoplasm that are targeted to the cytoplasm of the host cell. Possible mechanisms for this trans-trimembrane protein transport process are discussed.

Effect of Bdellovibrio bacteriovorus infection on the phosphoenolpyruvate:sugar phosphotransferase system in Escherichia coli: evidence for activation of cytoplasmic proteolysis

Intact cells of Bdellovibrio bacteriovorus strain 109J were found to be incapable of taking up 14C-methyl alpha-glucoside, mannitol or fructose, and extracts derived from these cells exhibited negligible activities of the protein components of the phosphoenolpyruvate:sugar phosphotransferase system (PTS). Escherichia coli strain ML35 cells exhibited high in vivo sugar uptake activities that were progressively lost over a period of 2 h at 30 degrees C following the entry of B. bacteriovorus into the periplasm of E. coli. In vitro complementation assays revealed that the E. coli PTS enzymes, enzyme I, HPr, and the glucose- and mannitol-specific enzymes II, were all lost almost in parallel with the disappearance of uptake activity. Thus, loss of activity in vivo was not due to membrane leakiness, energy depletion, or preferential inhibition or inactivation of any one protein component of the PTS. Instead, loss of PTS activity was attributed to digestion of the protein constituents of the system by proteases present in the cytoplasm of the host cell after bdellovibrio entry. Both ethylenediaminetetraacetate and phenylmethylsulphonyl fluoride partially protected against inactivation in vitro, and the two inhibitors together gave full protection, suggesting that both metallo- and seryl-proteases were responsible for the inactivation. Protease activity increased progressively with time following bdellovibrio entry and appeared to degrade the E. coli PTS enzymes in vivo. Preliminary evidence suggested that the proteases responsible for PTS enzyme degradation may be encoded by the B. bacteriovorus chromosome.

Protein composition of Bdellovibrio bacteriovorus and Escherichia coli membranes during their interaction

A comparative study of membrane proteins of Bdellovibrio bacteriovorus and host-bacteria Escherichia coli was performed by polyacrylamide gel electrophoresis in presence of sodium dodecyl sulphate. Infection of E. coli cells by bdellovibrions resulted in the loss of some high-molecular proteins and appearance of new ones in the host-bacteria membranes. The possible role of parasite proteases in degradation of host-bacteria membrane proteins is discussed.

Regulated breakdown of Escherichia coli deoxyribonucleic acid during intraperiplasmic growth of Bdellovibrio bacteriovorus 109J

During growth of Bdellovibrio bacteriovorus on [2-14C]deoxythymidine-labeled Escherichia coli, approximately 30% of the radioactivity was released to the culture fluid as nucleoside monophosphates and free bases; the remainder was incorporated by the bdellovibrio. By 60 min after bdellovibrio attack, when only 10% of the E. coli deoxyribonucleic acid (DNA) had been solubilized, the substrate cell DNA was degraded to 5 X 10(5)-dalton fragments retained within the bdelloplast. Kinetic studies showed these fragments were formed as the result of sequential accumulation of single- and then double-strand cuts. DNA fragments between 2 X 10(3) and 5 X 10(5) daltons were never observed. Chloramphenicol, added at various times after initiation of bdellovibrio intraperiplasmic growth on normal or on heated E. coli, which have inactivated deoxyribonucleases, inhibited further breakdown and solubilization of substrate cell DNA. Analysis of these intraperiplasmic culture deoxyribonuclease activities showed that bdellovibrio deoxyribonucleases are synthesized while E. coli nucleases are inactivated. It is concluded that continuous and sequential synthesis of bdellovibrio deoxyribonucleases of apparently differing specificities is necessary for complete breakdown and solubilization of substrate cell DNA, and that substrate cell deoxyribonucleases are not involved in any significant way in the degradation process.

Intraperiplasmic growth of Bdellovibrio bacteriovorus 109J: attachment of long-chain fatty acids to escherichia coli peptidoglycan

During the initial stages of intraperiplasmic growth of Bdellovibrio bacteriovorus on Escherichia coli, the peptidoglycan of the E. coli becomes acylated with long-chain fatty acids, primarily palmitic acid (60%) and oleic acid (20%). The attachment of the fatty acids to the peptidoglycan involves a carboxylic-ester bond, i.e., they were removed by treatment with alkaline hydroxylamine. Their linkage to the peptidoglycan does not involve a protein molecule. When the bdelloplast peptidoglycan was digested with lysozyme, the fatty acid-containing split products behaved as lipopeptidoglycan, i.e., they were extracted into the organic phase of 1-butanol:acetic acid:water (4:15) two-phase system; all of the lysozyme split products generated from normal E. coli peptidoglycan were extracted into the water phase. It is suggested that the function of the acylation reaction is to help stabilize the bdelloplast outer membrane against osmotic forces. In addition, a model is presented to explain how a bdellovibrio penetrates, stabilizes, and lyses a substrate cell.

Intraperiplasmic growth of Bdellovibrio bacteriovorus on heat-treated Escherichia coli

Heat treatment (55 degrees C for 40 min) of cell suspensions in buffer (ca. 3 x 10(9) cells per ml) of Escherichia coli ML35 caused a 4- to 4.5-log loss of cell viability. Similar results were found for several other E. coli strains that were examined. As a result of this heat treatment, 260-nm- and 280-nm-absorbing materials were released into the suspending buffer, along with about 10% of the total cellular radioactivity, when cells uniformly labeled with (14)C were used. In comparison with untreated cells, heat-treated E. coli ML35 cells showed (i) no significant changes in macromolecular composition other than ca. 22% less RNA content, (ii) an increased permeability to o-nitrophenyl-beta-d-galactopyranoside (a compound to which untreated cells are impermeable), (iii) almost complete loss of respiratory potential, and (iv) substantial losses of numerous glycolytic enzyme activities in cell extracts prepared from these cells. Intraperiplasmic development of Bdellovibrio bacteriovorus 109J with heat-treated E. coli ML35 as substrate cells appeared normal when observed microscopically, although bdellovibrio attachment and resultant bdelloplast formation were slightly retarded. No significant changes were observed in cell yields or in the ratios and contents of DNA, RNA, or protein between bdellovibrios harvested from untreated cells and those from heat-treated substrate cells after single-developmental-cycle growth on these cells. The average Y(ATP) values for intraperiplasmic growth on untreated and heat-treated substrate cells were 16.0 and 17.9, respectively. It is concluded that intraperiplasmic bdellovibrio growth on gently heat-treated E. coli substrate cells is very similar to growth on untreated substrate cells, even though the former substrate cells are nonviable and substantially impaired in many metabolic activities.

Glycolytic and tricarboxylic acid cycle enzyme activities during intraperiplasmic growth of Bdellovibrio bacteriovorus on Escherichia coli

Selected enzyme activities were measured in extracts of the total cell pellets obtained at various times during aerobic intraperiplasmic growth of Bdellovibrio bacteriovorus 109J on anaerobically grown Escherichia coli substrate cells. Initially, the glycolytic enzyme activities were associated with the input of E. coli and the tricarboxylic acid cycle enzyme activities with the input of bdellovibrios. During the first 90 min of Bdellovibrio development, the glycolytic activities declined about 25 to 60%, whereas the tricarboxylic acid cycle activities increased about 10%. Between 110 and 180 min, the glycolytic activities decreased to trace levels and tricarboxylic acid cycle activities increased about 50 to 90%. Both bdellovibrio cell extracts and the cell-free growth menstruum (obtained after bdellovibrio growth on E. coli) caused the inactivation of glycolytic enzymes in E. coli extracts.

Ribonucleic acid destruction and synthesis during intraperiplasmic growth of Bdellovibrio bacteriovorus

During growth of Bdellovibrio bacteriovorus on (2-14C)uracil-labeled Escherichia coli approximately 50% of the radioactivity is incorporated by the bdellovibrio and most of the remainder is released as free nucleic acid bases. Kinetic studies showed that 50 and 30S ribosomal particles and 23 and 16S ribosomal ribonucleic acid (RNA) of E. coli are almost completely degraded by the first 90 min in a 210- to 240-min bdellovibrio developmental cycle. Synthesis of bdellovibrio ribosomal RNA was first detected after 90 min. The specific activity and the ratio of radioactivity in the bases of the synthesized bdellovibrio RNA was essentially the same as those of the substrate E. coli. The total radioactivity of the bdellovibrio deoxyribonucleic acid (DNA) exceeded that in the DNA of the substrate E. coli cell, and the ratio of radioactivity of cytosine to thymine residues differed. Intraperiplasmic growth of B. bacteriovorus in the presence of added nucleoside monophosphates (singly or in combination) significantly decreased the uptake of radioactivity from (2-14C)uracil-labeled E. coli; nucleosides or nucleic acid bases did not. It is concluded that the RNA of the substrate cell, in the form of nucleoside monophosphates, is the major or exclusive precursor of the bdellovirbrio RNA and also serves as a precursor for some of the bdellovibrio DNA.

Interaction between Bdellovibrio bacteriovorus and the cytoplasmic membrane of Escherichia coli B

Adsorption of Bdellovibrio bacteriovours (Bdv) on the surface of Escherichia coli is accompanied by a sharp decrease in the initial rate of entry of alpha-methylglucoside-C-14 and thiomethlgalactopyranoside-C-14 into the host cell. Interaction between the parasite and E. coli leads to the rapid departure of previously accumulated labeled glucosides and beta-galactosides from the bacteria. Meanwhile the ATPcontent in E. coli falls sharply. Adsorption Bdv E.coli spheroplasts was established as a fact. The possible mechanisms of interaction between Bvd and the host cell at the cytoplasmic membrane level are discussed.

Kinetics of deoxyribonucleic acid destruction and synthesis during growth of Bdellovibrio bacteriovorus strain 109D on pseudomonas putida and escherichia coli

During the growth of Bdellovibrio bacteriovorus on Pseudomonas putida or Escherichia coli in either 10(-3)m tris(hydroxymethyl)aminomethane or in dilute nutrient broth, the host deoxyribonucleic acid (DNA) was rapidly degraded, and by 30 to 60 min after the initiation of the bdellovibrio development cycle essentially all host DNA became nonbandable in CsCl gradients. At this stage the host DNA degradation products were nondiffusable, and there was no appreciable pool of low-molecular-weight (cold acid soluble) DNA fragments in the cells or in the suspending medium. Bdellovibrio DNA synthesis occurred only after degradation of host DNA to a nonbandable form was complete. The synthesis occurred in a continuous fashion with P. putida as the host and in two separate periods with E. coli as host. By using E. coli containing a (3)H-thymidine label, it was shown that 73%, on the average, of the thymine residues of host DNA were incorporated into bdellovibrio DNA when E. coli was the only source of nutrient. In the presence of dilute nutrient broth, the host cells still served as the major source of precursors for bdellovibrio DNA synthesis, with only 20% of the precursors arising from the exogenous nutrients. The data indicate an efficient and controlled utilization of host DNA by the bdellovibrio. The host DNA is apparently degraded early in the developmental cycle to oligonucleotides of intermediate molecular weight from which the biosynthetic monomers are generated only as they become needed for bdellovibrio DNA synthesis.

Three-membered parasitic system: a bacteriophage, Bdellovibrio bacteriovorus, and Escherichia coli

Two bacteriophages for Bdellovibrio bacteriovorus were isolated. One of the phages (VL-1) was isolated on a host-independent Bdellovibrio strain, and the other (VL-2) was isolated on a host-dependent strain. Both phages grew on host-dependent as well as on host-independent Bdellovibrio strains. The development of the phages in host-dependent bdellovibrios occurred only when the phage-infected bdellovibrios parasitized cells of other bacteria. In the absence of other bacteria, the phages adsorbed to the bdellovibrios and killed them and in the process lost their own plaque-forming ability.