Molecular heterogeneity of the Bdellovibrios: evidence of two new species

Predatory Bacteria in the Treatment of Infectious Diseases and Beyond

Antimicrobial resistance (AMR) is an increasing problem worldwide, with significant associated morbidity and mortality. Given the slow production of new antimicrobials, non-antimicrobial methods for treating infections with significant AMR are required. This review examines the potential of predatory bacteria to combat infectious diseases, particularly those caused by pathogens with AMR. Predatory bacteria already have well-known applications beyond medicine, such as in the food industry, biocontrol, and wastewater treatment. Regarding their potential for use in treating infections, several in vitro studies have shown their potential in eliminating various pathogens, including those resistant to multiple antibiotics, and they also suggest minimal immune stimulation and cytotoxicity by predatory bacteria. In vivo animal studies have demonstrated safety and efficacy in reducing bacterial burden in various infection models. However, results can be inconsistent, suggesting dependence on factors like the animal model and the infecting bacteria. Until now, no clinical study in humans exists, but as experience with predatory bacteria grows, future studies including clinical studies in humans could be designed to evaluate their efficacy and safety in humans, thus leading to the potential for approval of a novel method for treating infectious diseases by bacteria.

Predatory bacteria as potential biofilm control and eradication agents in the food industry

Biofilms are a major concern within the food industry since they have the potential to reduce productivity in situ (within the field), impact food stability and storage, and cause downstream food poisoning. Within this review, predatory bacteria as potential biofilm control and eradication agents are discussed, with a particular emphasis on the intraperiplasmic Bdellovibrio-and-like organism (BALO) grouping. After providing a brief overview of predatory bacteria and their activities, focus is given to how BALOs fulfill four attributes that are essential for biocontrol agents to be successful in the food industry: (1) Broad spectrum activity against pathogens, both plant and human; (2) Activity against biofilms; (3) Safety towards humans and animals; and (4) Compatibility with food. As predatory bacteria possess all of these characteristics, they represent a novel form of biofilm biocontrol that is ripe for use within the food industry.

Environmental Regulation of the Distribution and Ecology of Bdellovibrio and Like Organisms

The impact of key environmental factors, salinity, prey, and temperature, on the survival and ecology of Bdellovibrio and like bacteria (BALOs), including the freshwater/terrestrial, non-halotolerant group and the halophilic Halobacteriovorax strains, has been assessed based on a review of data in the literature. These topics have been studied by numerous investigators for nearly six decades now, and much valuable information has been amassed and reported. The collective data shows that salinity, prey, and temperature play a major role in, not only the growth and survival of BALOs, but also the structure and composition of BALO communities and the distribution of the predators. Salinity is a major determinant in the selection of BALO habitats, distribution, prey bacteria, and systematics. Halophilic BALOs require salt for cellular functions and are found only in saltwater habitats, and prey primarily on saltwater bacteria. To the contrary, freshwater/terrestrial BALOs are non-halotolerant and inhibited by salt concentrations greater than 0.5%, and are restricted to freshwater, soils, and other low salt environments. They prey preferentially on bacteria in the same habitats. The halophilic BALOs are further separated on the basis of their tolerance to various salt concentrations. Some strains are found in low salt environments and others in high salt regions. In situ studies have demonstrated that salinity gradients in estuarine systems govern the type of BALO communities that will persist within a specific gradient. Bacterial prey for BALOs functions more than just being a substrate for the predators and include the potential for different prey species to structure the BALO community at the phylotype level. The pattern of susceptibility or resistance of various bacteria species has been used almost universally to differentiate strains of new BALO isolates. However, the method suffers from a lack of uniformity among different laboratories. The use of molecular methods such as comparative analysis of the 16S rDNA gene and metagenomics have provided more specific approaches to distinguished between isolates. Differences in temperature growth range among different BALO groups and strains have been demonstrated in many laboratory experiments. The temperature optima and growth range for the saltwater BALOs is typically lower than that of the freshwater/terrestrial BALOs. The collective data shows not only that environmental factors have a great impact on BALO ecology, but also how the various factors affect BALO populations in nature.

Description of Pseudobacteriovorax antillogorgiicola gen. nov., sp. nov., a bacterium isolated from the gorgonian octocoral Antillogorgia elisabethae, belonging to the family Pseudobacteriovoracaceae fam. nov., within the order Bdellovibrionales

A bacterial strain designated RKEM611T was isolated from the octocoral Antillogorgia elisabethae, collected off the coast of San Salvador, The Bahamas. The strain is Gram-stain-negative, an obligate aerobe, and pleomorphic. It requires NaCl for growth and exhibits optimal growth at 1–2 % (w/v) NaCl, 30–37 °C and pH 6.0–8.0. The predominant cellular fatty acids are C16 : 1ω5c and C16 : 0; the major respiratory quinone is menaquinone MK-6, and the DNA G+C content is 46.3 mol%. Based on phylogenetic analysis of the 16S rRNA gene, in addition to phenotypic characteristics, RKEM611T represents a novel species and genus of a novel family within the order Bdellovibrionales . The names Pseudobacteriovoracaceae fam. nov. and Pseudobacteriovorax antillogorgiicola gen., nov., sp., nov. are proposed. Isolate RKEM611T ( = NCCB 100521T = LMG 28452T) is the type strain.

Reclassification of Bacteriovorax marinus as Halobacteriovorax marinus gen. nov., comb. nov. and Bacteriovorax litoralis as Halobacteriovorax litoralis comb. nov.; description of Halobacteriovoraceae fam. nov. in the class Deltaproteobacteria

The taxonomic status of saltwater Bdellovibrio-like prokaryotic predators has been revised to assign species to Halobacteriovorax gen. nov. A reclassification of Bacteriovorax marinus as Halobacteriovorax marinus comb. nov. (type strain ATCC BAA-682(T) = DSM 15412(T)) and Bacteriovorax litoralis as Halobacteriovorax litoralis comb. nov. (type strain ATCC BAA-684(T) = DSM 15409(T)) is proposed. This revision is necessary because a previous proposal to retain saltwater isolates as species of Bacteriovorax and reclassify Bacteriovorax stolpii as Bacteriolyticum stolpii was not approved. The type species of a genus cannot be reassigned to another genus. Bacteriovorax stolpii is thus retained as the type species of Bacteriovorax and Halobacteriovorax marinus is the type species of Halobacteriovorax and of Halobacteriovoraceae fam. nov.

Abundance, diversity and seasonal dynamics of predatory bacteria in aquaculture zero discharge systems

Standard aquaculture generates large-scale pollution and strains water resources. In aquaculture using zero discharge systems (ZDS), highly efficient fish growth and water recycling are combined. The wastewater stream is directed through compartments in which beneficial microbial activities induced by creating suitable environmental conditions remove biological and chemical pollutants, alleviating both problems. Bacterial predators, preying on bacterial populations in the ZDS, may affect their diversity, composition and functional redundancy, yet in-depth understanding of this phenomenon is lacking. The dynamics of populations belonging to the obligate predators Bdellovibrio and like organisms (BALOs) were analyzed in freshwater and saline ZDS over a 7-month period using QPCR targeting the Bdellovibrionaceae, and the Bacteriovorax and Bacteriolyticum genera in the Bacteriovoracaeae. Both families co-existed in ZDS compartments, constituting 0.13-1.4% of total Bacteria. Relative predator abundance varied according to the environmental conditions prevailing in different compartments, most notably salinity. Strikingly, the Bdellovibrionaceae, hitherto only retrieved from freshwater and soil, also populated the saline system. In addition to the detected BALOs, other potential predators were highly abundant, especially from the Myxococcales. Among the general bacterial population, Flavobacteria, Bacteroidetes, Fusobacteriaceae and unclassified Bacteria dominated a well mixed but seasonally fluctuating diverse community of up to 238 operational taxonomic units, as revealed by 16S rRNA gene sequencing.

A small predatory core genome in the divergent marine Bacteriovorax marinus SJ and the terrestrial Bdellovibrio bacteriovorus

Bacteriovorax marinus SJ is a predatory delta-proteobacterium isolated from a marine environment. The genome sequence of this strain provides an interesting contrast to that of the terrestrial predatory bacterium Bdellovibrio bacteriovorus HD100. Based on their predatory lifestyle, Bacteriovorax were originally designated as members of the genus Bdellovibrio but subsequently were re-assigned to a new genus and family based on genetic and phenotypic differences. B. marinus attaches to gram-negative bacteria, penetrates through the cell wall to form a bdelloplast, in which it replicates, as shown using microscopy. Bacteriovorax is distinct, as it shares only 30% of its gene products with its closest sequenced relatives. Remarkably, 34% of predicted genes over 500 nt in length were completely unique with no significant matches in the databases. As expected, Bacteriovorax shares several characteristic loci with the other delta-proteobacteria. A geneset shared between Bacteriovorax and Bdellovibrio that is not conserved among other delta-proteobacteria such as Myxobacteria (which destroy prey bacteria externally via lysis), or the non-predatory Desulfo-bacteria and Geobacter species was identified. These 291 gene orthologues common to both Bacteriovorax and Bdellovibrio may be the key indicators of host-interaction predatory-specific processes required for prey entry. The locus from Bdellovibrio bacteriovorus is implicated in the switch from predatory to prey/host-independent growth. Although the locus is conserved in B. marinus, the sequence has only limited similarity. The results of this study advance understanding of both the similarities and differences between Bdellovibrio and Bacteriovorax and confirm the distant relationship between the two and their separation into different families.

Bdellovibrio exovorus sp. nov., a novel predator of Caulobacter crescentus

The life cycle, prey range and taxonomic status of a Bdellovibrio-like organism, strain JSS(T), were studied. Strain JSS(T) was isolated from sewage in London, Ontario, Canada, in enrichment culture with Caulobacter crescentus prey cells. During predation, this strain remained attached to the outside of a stalked C. crescentus cell. No periplasmic growth stage was observed and no bdelloplast was formed. The stalked cells of C. crescentus retained their shape and, after predation, were devoid of cytoplasmic content, as shown by transmission electron microscopy. A periplasmic growth stage has been a definitive character in the description of members of the genera Bdellovibrio, Bacteriovorax, Bacteriolyticum and Peredibacter. This is the first description of an epibiotic predator in this group of prokaryotic predators. The G+C content of the genomic DNA of strain JSS(T) was 46.1 mol%. 16S rRNA gene sequence analysis showed that this strain was related to Bdellovibrio bacteriovorus strains HD100(T), 109J, 114 and 127 (90-93 % similarity). Phylogenetic analysis based on 16S rRNA gene sequences grouped strain JSS(T) with the Bdellovibrio cluster, but at a distance from other Bdellovibrio isolates. On the basis of features of the life cycle and phylogenetic data, it was concluded that strain JSS(T) merits classification as the type strain of a novel species, for which the name Bdellovibrio exovorus sp. nov. is proposed (type strain JSS(T) =ATCC BAA-2330(T) = DSM 25223(T)).

Global survey of diversity among environmental saltwater Bacteriovoracaceae

Halophilic Bacteriovorax (Bx), formerly known as the marine Bdellovibrio, are Gram-negative, predatory bacteria found in saltwater systems. To assess their genetic diversity and geographical occurrence, the small subunit rRNA (ssu-rRNA) gene sequences were analysed from 111 marine, salt lake and estuarine isolates recovered from 27 locations around the world. Phylogenetic analysis of these isolates using Geobacter as the outgroup revealed eight distinct ribotype clusters each with at least two isolates. Each cluster was composed of isolates with >or= 96.5% similarity in ssu-rRNA sequences. Three single isolate outliers were observed. Many of the Bx ribotypes were widely dispersed among different types of ecosystems (e.g. cluster III was recovered from the Great Salt Lake, the Atlantic Ocean, Pacific Ocean, Chesapeake Bay and gills of aquarium fish). However, cluster V was only recovered from a single ecosystem, estuaries. Cluster V was originally detected in the Chesapeake Bay and subsequently in the Pamlico Sound/Neuse River system. Principal coordinate analysis revealed that the sequences of the isolates from different environments were distinct from each other. The results of this study reveal the saltwater Bx to be phylogenetically and environmentally more diverse than was previously known.

Diversity and evolution of Bdellovibrio-and-like organisms (BALOs), reclassification of Bacteriovorax starrii as Peredibacter starrii gen. nov., comb. nov., and description of the Bacteriovorax–Peredibacter clade as Bacteriovoracaceae fam. nov

A phylogenetic analysis of Bdellovibrio-and-like organisms (BALOs) was performed. It was based on the characterization of 71 strains and on all consequent 16S rRNA gene sequences available in databases, including clones identified by data-mining, totalling 120 strains from very varied biotopes. Amplified rDNA restriction analysis (ARDRA) accurately reflected the diversity and phylogenetic affiliation of BALOs, thereby providing an efficient screening tool. Extensive phylogenetic analysis of the 16S rRNA gene sequences revealed great diversity within the Bdellovibrio (>14 % divergence) and Bacteriovorax (>16 %) clades, which comprised nine and eight clusters, respectively, exhibiting more than 3 % intra-cluster divergence. The clades diverged by more than 20 %. The analysis of conserved 16S rRNA secondary structures showed that Bdellovibrio contained motifs atypical of the δ-Proteobacteria, suggesting that it is ancestral to Bacteriovorax. While none of the Bdellovibrio strains were of marine origin, Bacteriovorax included separate soil/freshwater and marine-specific groups. On the basis of their extensive diversity and the large distance separating the groups, it is proposed that Bacteriovorax starrii be placed into a new genus, Peredibacter gen. nov., with Peredibacter starrii A3.12T (=ATCC 15145T=NCCB 72004T) as its type strain. Also proposed is a redefinition of the Bdellovibrio and the Bacteriovorax–Peredibacter lineages as two different families, i.e. ‘Bdellovibrionaceae’ and a new family, Bacteriovoracaceae. Also, a re-evaluation of oligonucleotides targeting BALOs is presented, and the implications of the large diversity of these organisms and of their distribution in very different environments are discussed.

Reclassification of salt-water Bdellovibrio sp. as Bacteriovorax marinus sp. nov. and Bacteriovorax litoralis sp. nov

Bdellovibrios are unique, predatory bacteria with an intraperiplasmic growth and multiplication phase within their prey, which consists of many Gram-negative bacteria. Until recently, all bacteria that exhibited these traits were included in the genus Bdellovibrio. However, analysis of 16S rDNA sequences and other studies have demonstrated substantial genotypic, phenotypic and ecotypic diversity among the organisms in this genus (Baer et al., 2000; Snyder et al., 2002). This has resulted in reclassification of Bdellovibrio stolpii and Bdellovibrio starrii into the newly constructed genus Bacteriovorax (Baer et al., 2000). In this study, examination of marine isolates of Bdellovibrio (designated SJT, AQ and JS5T) has revealed them to be related more closely to the newly designated genus Bacteriovorax. Phylogenetic analysis of 16S rRNA gene sequences revealed that marine isolates SJT, AQ and JS5T clustered in a separate clade from Bdellovibrio bacteriovorus 100T as part of the clade that contains Bacteriovorax spp., indicating a much closer taxonomic relationship to the latter. DNA-DNA hybridization experiments also demonstrated <5 % similarity between Bdellovibrio bacteriovorus 100T and the marine isolates. Distinct differences between the salt-water group and Bdellovibrio spp. were also observed by determination of DNA G+C content, salinity growth testing and antibiotic sensitivity analysis. On the basis of the results from the studies described above, it is proposed that marine isolates SJT (=ATCC BAA-682T=DSM 15412T) and JS5T (=ATCC BAA-684T=DSM 15409T) should be classified within the genus Bacteriovorax as the type strains of Bacteriovorax marinus sp. nov. and Bacteriovorax litoralis sp. nov., respectively.

Taxonomic studies of predatory bdellovibrios based on 16S rRNA analysis, ribotyping and the hit locus and characterization of isolates from the gut of animals

The aim of our study was to obtain data for the molecular characterization of bdellovibrio bacteria, which were recently split into the genus Bdellovibrio and the newly designated genus Bacteriovorax. We determined the 16S rDNA sequences of five reference strains and performed a phylogenetic analysis including published 16S rRNA sequences of bdellovibrios. A comparison of the secondary structure showed significant differences in two regions of the 16S rRNAs of the species Bdellovibrio bacteriovorus, Bacteriovorax starrii, and Bacteriovorax stolpii. In addition, ribotyping techniques gave specific hybridization patterns and revealed that two rRNA operons are present in the investigated strains. A hybridization probe derived from the genetic locus hit, associated with the host independent (HI) phenotype of B. bacteriovorus, was found to be specific for this species. Sequence comparison of the hit locus revealed few base pair changes between host independent (HI) and host dependent (HD) strains. Ribotyping and hybridization experiments using the hit probe were applied to characterize bdellovibrio strains isolated from the gut of animals and humans and one isolate from sewage.

Prey range characterization, ribotyping, and diversity of soil and rhizosphere Bdellovibrio spp. isolated on phytopathogenic bacteria

Thirty new Bdellovibrio strains were isolated from an agricultural soil and from the rhizosphere of plants grown in that soil. Using a combined molecular and culture-based approach, we found that the soil bdellovibrios included subpopulations of organisms that differed from rhizosphere bdellovibrios. Thirteen soil and seven common bean rhizosphere Bdellovibrio strains were isolated when Pseudomonas corrugata was used as prey; seven and two soil strains were isolated when Erwinia carotovora subsp. carotovora and Agrobacterium tumefaciens, respectively, were used as prey; and one tomato rhizosphere strain was isolated when A. tumefaciens was used as prey. In soil and in the rhizosphere, depending on the prey cells used, the concentrations of bdellovibrios were between 3 x 10(2) to 6 x 10(3) and 2.8 x 10(2) to 2.3 x 10(4) PFU g(-1). A prey range analysis of five soil and rhizosphere Bdellovibrio isolates performed with 22 substrate species, most of which were plant-pathogenic and plant growth-enhancing bacteria, revealed unique utilization patterns and differences between closely related prey cells. An approximately 830-bp fragment of the 16S rRNA genes of all of the Bdellovibrio strains used was obtained by PCR amplification by using a Bdellovibrio-specific primer combination. Soil and common bean rhizosphere strains produced two and one restriction patterns for this PCR product, respectively. The 16S rRNA genes of three soil isolates and three root-associated isolates were sequenced. One soil isolate belonged to the Bdellovibrio stolpii-Bdellovibrio starrii clade, while all of the other isolates clustered with Bdellovibrio bacteriovorus and formed two distantly related, heterogeneous groups.

A conjugation procedure for Bdellovibrio bacteriovorus and its use to identify DNA sequences that enhance the plaque-forming ability of a spontaneous host-independent mutant

Wild-type bdellovibrios are obligate intraperiplasmic parasites of other gram-negative bacteria. However, spontaneous mutants that can be cultured in the absence of host cells occur at a frequency of 10(-6) to 10(-7). Such host-independent (H-I) mutants generally display diminished intraperiplasmic-growth capabilities and form plaques that are smaller and more turbid than those formed by wild-type strains on lawns of host cells. An analysis of the gene(s) responsible for the H-I phenotype should provide significant insight into the nature of Bdellovibrio host dependence. Toward this end, a conjugation procedure to transfer both IncQ and IncP vectors from Escherichia coli to Bdellovibrio bacteriovorus was developed. It was found that IncQ-type plasmids were capable of autonomous replication in B. bacteriovorus, while IncP derivatives were not. However, IncP plasmids could be maintained in B. bacteriovorus via homologous recombination through cloned B. bacteriovorus DNA sequences. It was also found that genomic libraries of wild-type B. bacteriovorus 109J DNA constructed in the IncP cosmid pVK100 were stably maintained in E. coli; those constructed in the IncQ cosmid pBM33 were unstable. Finally, we used the conjugation procedure and the B. bacteriovorus libraries to identify a 5.6-kb BamHI fragment of wild-type B. bacteriovorus DNA that significantly enhanced the plaque-forming ability of an H-I mutant, B. bacteriovorus BB5.

Bdellovibrio host dependence: the search for signal molecules and genes that regulate the intraperiplasmic growth cycle

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Serogrouping of Halophilic Bdellovibrios from Chesapeake Bay and Environs by Immunodiffusion and Immunoelectrophoresis

Little has been reported on the serological relationship of halophilic bdellovibrios (Bd). Immunodiffusion analysis performed with rabbit or mouse Bd antisera developed against eight halophilic Bd isolates and one terrestrial Bd isolate, when reacted with soluble antigen preparations of 45 isolates of halophilic Bd, allowed separation into seven serogroups, which were distinct from the terrestrial isolate. Soluble antigen preparations of prey bacteria, Vibrio parahaemolyticus P-5 (P-5) and Escherichia coli ML 35 (ML 35), exhibited no reactivity with the antisera by immunodiffusion. Immunoelectrophoresis revealed the presence of three distinct antigens in homologous reactions and one shared antigen in heterologous Bd reactions. Shared antigens were noted between halophilic and terrestrial Bd, in addition to between halophilic Bd strains, indicating the possible existence of an antigen(s) which may be shared among all Bd. Again, no shared antigen was noted when P-5 or ML 35 was allowed by immunoelectrophoresis to react with the antisera. Prey susceptibility testing of the seven distinct groups of halophilic Bd, using 20 test prey, produced essentially identical spectra for each group, indicating that this was not a useful technique in delineating the Bd. While immunoelectrophoresis was able to demonstrate an antigen common to all Bd tested, immunodiffusion was able to delineate strains on the basis of a “serogroup specific” antigen. This suggests that immunological tools may serve as important means to study the taxonomy of halophilic Bd, as well as in the formation of a clearer taxonomic picture of the genus Bdellovibrio.

Detection of polyphosphates and enzymes of polyphosphate metabolism in Bdellovibrio bacteriovorus

Bdellovibrio bacteriovorus cells, parasitizing in E. coli, contain a considerable amount of inorganic polyphosphates, 55% of the total pool of which is due to the most polymeric acid-insoluble polyphosphates. B. bacteriovorus contains enzymes participating both in the synthesis and consumption of polyphosphates, i.e. 1,3-diphosphoglycerate: polyphosphate phosphotransferase, polyphosphate glucokinase, polyphosphatase, tripolyphosphatase, pyrophosphatase, acid and alkaline phosphatases. The possible role of high-molecular polyphosphates in the vital activity of the bacterial parasite B. bacteriovorus is discussed.

Multiple forms of urease in cytoplasmic fractions of Ureaplasma urealyticum

The urease activity of Ureaplasma urealyticum was found to be located in the cytoplasmic fraction and consisted of multiple stable enzyme forms representing at least four biotypes.

Antigenicity of bdellovibrios

Antigenic relationships between 12 locally isolated bdellovibrios and 3 established reference strains (109D, 6-5-S, and UKi2) were investigated. Antigenicity of the strains was examined by use of the micro-complement fixation test, the serum and complement bactericidal test, and the immunodiffusion test. Antisera were prepared against one of the local strains (MS7) and against one of the established reference strains (UKi2). The complement fixation titers suggest a close relationship among all strains. Immunodiffusion tests produced lines of identity between the homologous strain MS7 and all other strains. It is suggested on the basis of these results that bdellovibrio may possess a common antigen.

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.

Lethal effect of fresh sea water on Vibrio parahaemolyticus and isolation of Bdellovibrio parasitic against the organism

Halophilic Bdellovibrio, which is parasitic and lytic to Vibrio pharahaemolyticus, was ioslated from fresh sea water in the winter. It had a lethal effect on V. parahaemolyticus. The optimum temperature ofr multiplication ranged from 25 C to 30 C and growth was not observed at 35 C. Plaque numbers of the isolate reached a maximum in 17 hr under conditions of shaking at 25 C in autoclaved sea water supplemented with V. parahaemolyticus cells, and were as high as ten times the number of host cells. With respect to the host-suspended medium, the isolate multiplied in natural sea water ten times more than in Herbst's artificial sea water but did not grow in saline. V. parahaemolyticus, Vibrio alginolyticus and several species in the Vibrio genus were susceptible to the parasite on the basis of plaque formation but Escherichia coli and Staphylococcus aureus were not.

Application of the deoxyribonucleic acid/ribonucleic acid hybridization technique in Bdellovibrio as a model for studying ribonucleic acid turnover in host-parasite systems

The kinetics of host ribonucleic acid (RNA) degradation and its resynthesis into Bdellovibrio-specific polyribonucleotides has been studied. The kinetics of RNA turnover was followed during a one-step synchronous growth cycle of Bdellovibrio growing within 32-po4-Labeled Escherichia coli host cells. The species of labeled RNA present at any given time was ascertained through the specificity of the deoxyribonuclei acid (DNA)/RNA hybridization technique. At nearsaturating levels of RNA and at zero time, 7% of the host DNA sequences and only 0.04% of the Bdellovibrio DNA became hybridized with 32-P-labeled host cell RNA (greater than 99% host specific). At the end of the burst, 98% of the labeled RNA sequences were specific for Bdellovibrio DNA. About 74% of the initial labeled host cell RNA became turned over into Bdellovibrio-specific sequences. We provide data indicating that host cell ribosomal RNA is assimilated by Bdellovibri. Degradation of host cell RNA occurs in a gradual fashion over most of the Bdellovibrio developmental growth cycle. This application of the DNA/RNA hybridization technique and its general concept should be of value in elucidating the kinetics of nucleic acid turnover in other types of host-parasite systems.

Energy metabolism of Bdellovibrio bacteriovorus. I. Energy production, ATP pool, energy charge

Bdellovibrio bacteriovorus, strain Bd. 109 Sa, generates ATP mainly by oxidative phosphorylation during electron transport. During exponential growth the ATP pool is constant (9 mmoles/100 mugN) indicating that energy-producing and energy-consuming reactions are well balanced. The ratio of substrate respiration/endogenous respiration is approx. 2.5/1. Energy charge is constant both in endogenous and substrate respiration at values of 0.62 to 0.64. During endogenous respiration (starvation) the ATP pool oscillates at regular intervals. ATP over-production is started after the ATP pool has decreased to a minimum level of 6 nmoles/100 mug N. The alternating over- and under-production of ATP is interpreted as a special regulation which enables the organism to make economic use of its own cellular materials. Addition of substrate (glutamate) to starving cells does not influence the type of ATP pool oscillation as observed in endogenous respiration. The parasitic strain Bd. 109 Pa exhibits the same periodicity of ATP overproduction as does it saprophytic derivative, Bd. 109 Sa. Decrease of viability during starvation is paralleled by a decrease of the ATP pool.

Incorporation of long-chain fatty acids of the substrate organism by Bdellovibrio bacteriovorus during intraperiplasmic growth

Data are presented showing that a large proportion of the fatty acids of Bdellovibrio bacteriovorus grown intraperiplasmically are derived unaltered from the fatty acids of its substrate organism. Those fatty acids of the bdellovibrio not homologous with those of the substrate organism are derived mainly by metabolic alteration of preexisting fatty acids in the latter. De novo synthesis from acetate occurs only to a small extent. These characteristics of bdellovibrio physiology are in part responsible for its minimal energy expenditure for intraperiplasmic growth. The data presented also indicate that B. bacteriovorus is capable of hydrogenating unsaturated fatty acids, of beta-oxidation of fatty acids, and of regulating the proportion of saturated and unsaturated fatty acids in the lipids.

Altered proteins with triosephosphate isomerase activity in suppressor-containing strains of Bacillus subtilis

Suppressor mutations in Bacillus subtilis cause the synthesis of a new protein with the enzymatic activity of l-leucine dehydrogenase and two groups of new proteins with the activity of triosephosphate isomerase. The new isoenzymes of triosephosphate isomerase are separable by zone electrophoresis and differ among themselves in elution behavior upon gel permeation chromatography. One group has an apparent average molecular weight of 120,000 to 135,000, which is more than twice that of the wild-type enzyme. Another group appears to be even higher in molecular weight. These data are consistent with the working hypothesis that the new isoenzymes are produced by extension of growing polypeptide chains through one or more chain-terminating triplets, although other mechanisms resulting in alteration of shapes, charges, or associations of the enzymes are not excluded.

Isolation and characterization of temperature-sensitive mutants of host-dependent Bdellovibrio bacteriovorus 109D

A variety of temperature-sensitive mutants of host-dependent Bdellovibrio bacteriovorus 109D were selected after ethyl methane sulfonate mutagenesis. Mutants that demonstrated plaque-forming ability reversion frequencies of 10(-8) to 10(-9) were chosen for further study. Representatives of these mutants were then characterized by phase-contrast and electron microscopy, temperature-shifted one-step growth experiments, attachment kinetics, and macromolecular capabilities. Representative mutants demonstrate various types of blockage corresponding to the previously described morphological stages of Bdellovibrio predatious life cycle, i.e., attachment blockage (109D153), penetration blockage (109D3 and 109D48), and blockage of intracellular growth (109D4 and 109D152). The time of release from temperature repression for the mutant classes was found to correspond to the apparent morphological stage of blockage via temperature-shifted, one-step growth experiments. Mutants characterized as exhibiting blockage in the penetration or intracellular stages of the infection cycle exhibited, at the permissive and nonpermissive temperatures, kinetics of attachment to Escherichia coli WP2 similar to those of the wild type. One mutant, 109D153, exhibited depressed attachment at the restrictive temperature even though the Bdellovibrio cells were motile. The extent of 38.5 C attachment of 109D153 to E. coli is at the same level as that of wild-type 109D to Bacillus subtilis, a gram-positive, non-host organism. Subsequent detachments were revealed in the wild-type 109D-B. subtilis or mutant 109D153-Escherichia coli (38.5 C) cultures. These studies reveal a biphasic attachment phenomenon in the early interaction of Bdellovibrio with its host. It appears that, at the restrictive temperature, 109D153 is capable only of the initial, nonspecific type of attachment.

Growth cycle of predacious Bdellovibrios in a host-free extract system and some properties of the host extract

Host-free growth and reproduction of a host-dependent strain of Bdellovibrio bacteriovorus incubated with an extract from host cells were studied. The morphological changes occurring in the cells were correlated with deoxyribonucleic acid (DNA) synthesis as measured by labeled nucleotide or orthophosphate incorporation. The host-free developmental cycle of Bdellovibrio is similar to that of the two-membered system; the early loss of flagella, the elongation into filaments, and multiple fission into flagellated progeny are typical for both host-free and intraperiplasmic development of bdellovibrios. Filament length and time of division appear to depend on the concentration of the host extract. Host extract was found to be heat stable and DNase stable, and Pronase sensitive and RNase sensitive. Addition of ribonucleic acid to the extract medium at various times during the Bdellovibrio growth cycle demonstrated that host extract is required continuously during the cycle for growth. The observations reported give a unified picture of Bdellovibrio development and allow for the suggestion that wild-type bdellovibrios depend upon the presence of some host factor for induction of DNA synthesis, whereas depletion of host factor triggers division. The ecological implications of such host dependence are discussed.

Respiration of Bdellovibrio bacteriovorus strain 109J and its energy substrates for intraperiplasmic growth

Measurements of oxidation rates, respiratory quotients (RQ), and release of (14)CO(2) from uniformly labeled substrates showed that glutamate, alpha-ketoglutarate, and synthetic and natural amino acid mixtures are oxidized by suspensions of Bdellovibrio bacteriovorus strain 109J. The oxidation of these substrates largely suppress the endogenous respiration of the Bdellovibrio cells and may or may not cause a small increase, 20 to 50%, in their rate of oxygen consumption. The failure of respired substrates to increase markedly the respiration rate of the Bdellovibrio cells over the endogenous value is discussed. Carbon from these substrates is incorporated into the Bdellovibrio cells during oxidation. Acetate is also oxidized, but its oxidation inhibits endogenous respiration by only about 40% and no acetate is assimilated. The RQ of the Bdellovibrio cells changes from a value characteristic of endogenous respiration to that characteristic of the oxidation of glutamate or of a balanced amino mixture very shortly after the attack of the Bdellovibrio cells on their prey, and the latter RQ is maintained during intraperiplasmic growth. Glutamate, or a mixture of amino acids in the external environment, contributes to the carbon dioxide produced by the Bdellovibrio cells growing intraperiplasmically. It is concluded from these data that amino acids, derived from the breakdown of the protein of the prey, serve as a major energy source during intraperiplasmic growth of B. bacteriovorus 108J. Insofar as they were tested, B. bacteriovorus strains 109D and A. 3. 12 were similar in respiration to strain 109J.

Isolation and preliminary characterization of bacteriophages for Bdellovibrio bacteriovorus

Ten bacteriophages that attack and lyse saprophytic strains of Bdellovibrio bacteriovorus were isolated. Morphological, serological, and host-range studies revealed that there were four different bdellovibrio phages present among the isolates. One of the phages lysed a strain of B. bacteriovorus that requires the presence of a suitable bacterial host for growth. The phage attached to the bdellovibrio cells in the absence of the bacterial host cells; lysis occurred only in the presence of host cells. The 19 saprophytic bdellovibrio strains employed in the phage host-range studies were grouped on the basis of their susceptibility to phage lysis.