Diversity of Extracellular Proteolytic Activities Among Prevotella Species from the Rumen

The current research was aimed at comparing proteolytic activities among ruminal Prevotella spp. Growth rates of Prevotella sp. 2202, Prevotella ruminicola D31d, P. brevis GA33, P. albensis M384, and P. bryantii B₁4 varied with N source, and no one N source produced the fastest growth in all species. Proteolytic activity was greatest with casein compared with peptides, AA, and NH₄Cl in all species. Proteolytic activity of Prevotella sp. 2202, P. brevis GA33, and P. bryantii B₁4 was modulated by N source. With gelatin co-polymerized SDS-PAGE, the extracellular activities of the Prevotella spp. showed wide variation in number, size, and type of proteases. Prevotella sp. 2202 and P. albensis M384 produced metalloproteases of low molecular weight (40 kDa). P. ruminicola D31d produced one cysteine protease (100–200 kDa) and two metalloproteases (90–100 kDa). P. brevis GA33 generated a diffuse clearing zone (95–160 kDa) containing serine, cysteine, and metalloproteases. P. bryantii B₁4 produced a metalloprotease greater than 200 kDa in size. The molecular sizes provided are estimations and served only to differentiate among the bacterial species in this study. Large variations in proteolytic activities among species and the known genetic diversity of the Prevotella taxon suggested that targeting this bacterial assemblage for genetic manipulation in order to alter the bacterial impact on ruminal protein degradation would be difficult. Received: 12 January 1999 / Accepted: 19 May 1999     

Lysogeny among mycobacteria

Our investigations to detect naturally lysogenic strains of mycobacteria were limited to 1 strain ofMycobacterium smegmatis, 4 strains ofMycobacterium borstelense var.niacinogenes, and to 5 strains ofMycobacterium marinum (Syn:Mycobacterium balnei), all together 10 strains. They were chosen because as a sign of lysis they secrete a large quantity of cytoplasmatic components (nucleic acids proteins, amino acids etc.) into the fluid medium (for instance phosphate buffer), in which they are suspended. In a first series of experiments culture filtrates were tested on 84 strains of slowly and rapidly growingMycobacterium species as indicator strains. Using this method free phage particles were only found in the culture filtrate of 1 strain,Mycobacterium smegmatis SN 46, isolated from a patient with achalasia. Phage particles could not be found in the filtrates of the other 9 probably lysogenic strains. In a second series of experiments more closely related indicator strains were used. The 10 probably lysogenic strains were cultured in bovine serum or antiphage-antiserum containing medium and single selected colony cultures a small part of which showed sensitivity to the filtrates. The released and adapted phages, designated as B₂₄, B₃₀, B₃₂, B₃₃, B₃₄ and B₃₅ have a very narrow host range. The plaques are very small and turbid. On electron micrographs the temperate phages B₂₄, B₃₀ and B₃₅ exhibit the typical head-tail morphology. The head of the temperateborstelense var.niacinogenes phage B₃₀ is 45 nm in diameter, the tength of tail is about, 120nm. The average dimensions of the long head ofsmegmatis phage B₂₄ are 40 × 80 nm, the tail is about 160 nm long. The balnei phage B₃₅ is very similar morphologically to phage B₃₀. The head is about 50 nm in diameter, the length of tail about 160 nm. The phage sensitive variants are not “carrier” strains. Their phage sensitivity is not a stable property. After several culture passages in serum-free medium the variants regain their phage immunity completely and release phages like the lysogenic parent strains. The sensitive variants must therefore be considered to be also lysogenic. TheMycobacterium borstelense var.niacinogenes phages are serologically very related. Dedicated to Academician Ivan Málek on the occasion of his 60th birthday     

Non-specific DNAases from the rumen bacteriumPrevotella bryantii

Extracellular non-specific nucleases were observed in some strains belonging to the ruminal species of the genusPrevotella, mostlyP. brevis andP. bryantii. The nuclease fromP. bryantii appeared to be extracellular; it mediates the degradation of the supercoiled plasmid DNAvia an open circle intermediate. The cleavage is not site specific although a preference for certain cleavage sites does seem to exist. Our attempts to clone the wild-typeP. bryantii B₁4 nuclease inE. coli strain ER1992 that reports on the DNA damage sustained, were unsuccessful probably due to excessive intracellular nuclease activity that killed the cells bearing the gene for the nuclease. On the other hand, the nuclease from a related strain TC1-1, which has a less active enzyme of the same type, was successfully cloned.     

Degradation and Utilization of Xylans by the Rumen AnaerobePrevotella bryantii(formerlyP. ruminicolasubsp.brevis) B14

Freshly harvested whole cells from cultures ofP. bryantiiB₁4 grown with oat spelt xylan (OSX) as an energy source showed less than 25% of the enzyme activity against OSX, and less than 15% of the activity against birchwood xylan (BWX) and carboxymethylcellulose, that was detectable in sonicated cell preparations. This indicates that much of this hydrolytic activity is either periplasmic, membrane-associated or intracellular and may be concerned with the processing of transported oligosaccharides.P. bryantiiB₁4 cultures were able to utilise up to 45% and 51% of the total pentose present in OSX and BWX, respectively, after 24 h, but could utilize 84% of a water-soluble fraction of BWX. Analysis of the xylan left undegraded after incubation withP. bryantiishowed that while xylose and arabinose were removed to a similar extent, uronic acids were utilized to a greater extent than xylose. Predigestion of xylans with two cloned xylanases from the cellulolytic rumen anaerobeRuminococcus flavefaciensgave little increase in overall pentose utilization suggesting that externalP. bryantiixylanases are as effective as the clonedR. flavefaciensenzymes in releasing products that can be utilised byP. bryantiicells. The xylanase system ofP. bryantiiis able to efficiently utilise not only xylo-oligosaccharides but also larger water-soluble xylan fragments.     

Identification and characterization of bacteriophages specific to the catfish pathogen,Edwardsiella ictaluri

Aims: To identify and characterize bacteriophages specific for Edwardsiella ictaluri, the causative agent for enteric septicemia of catfish (ESC). Methods and Results: Two bacteriophages were isolated that infect Edw. ictaluri. They both produce clear plaques, have icosahedral heads with a non‐rigid tail, and are tentatively classified as Siphoviridae. Phages ΦeiDWF and ΦeiAU are dsDNA viruses with approximate genome sizes of 40 and 45 kb, respectively. The addition of 500 μmol l^?1 CaCl₂ enhanced phage titres. Both phages have a latent period of 40 min and an estimated burst size of 270. Every Edw. ictaluri strain tested was susceptible to phage infection with variable plaquing efficiencies and with no evidence of lysogeny, with no plaques detected on other bacterial species. Conclusions: Two unique bacteriophages were isolated that show host‐specificity for Edw. ictaluri, have temperature and metal cation‐dependent infectivity, and are tentatively placed within the family Siphoviridae. Significance and Impact of the Study: This is the first report of bacteriophages specific to Edw. ictaluri, an important fish pathogen affecting farm‐raised channel catfish. Initial characterization of these bacteriophages has demonstrated their potential use as biotherapeutic and diagnostic agents associated with ESC.     

Ribosomal RNA genes from Prevotella bryantii: organization and heterogeneity

FiveP. bryantii B₁4 16S rRNA gene copies and their flanking regions were cloned and analyzed. A genomic library was constructed and screened with oligonucleotide DNA probe specific for 16S rRNA gene ofP. bryantii. Five out of six different copies of 16S RNA gene were recovered and sequenced. Only minor differences (0.3–1.2%) between copies were detected within the 1541 bp long sequence. The impact of the sequence variability of 16S rRNA gene copies on phylogenetic positioning ofP. bryantii was determined. All five sequences from clonedP. bryantii B₁4 16S rRNA genes were placed in the same operational taxonomy unit. Control regions of all five analyzed rRNA operatons were almost identical and three candidate for promoter sequences were identified by Neutral Network Promoter Prediction. Spacer regions between 16S-rRNA and 23S rRNA genes in all five cloned copies were 543 bp long and genes for tRNA^lle and tRNA^Ala were identified inside this regions.     

Phenotypic Characterization of Polysaccharidases Produced by Four Prevotella Type Strains

Four ruminal Prevotella type strains, P. ruminicola JCM8958^T, P. bryantii B₁4^T, P. albensis M384^T, and P. brevis ATCC19188^T, were characterized for polysaccharide-degrading activities with the reducing sugar release assay and zymogram analyses. Carboxymethylcellulase, xylanase, and polygalacturonate (PG)-degrading enzyme activities were determined in cultures grown on oat spelt xylan, xylose, arabinose, cellobiose, and glucose as sole growth substrates. P. ruminicola and P. albensis showed carboxymethylcellulase induction patterns. When xylan was supplied as a sole growth substrate, xylanase activities produced by P. bryantii and P. albensis were at least 18- and 11-fold higher, respectively, than during growth on other carbohydrates, suggesting that the regulation of the xylanases was highly specific to xylan. All strains constitutively produced PG-degrading enzymes. The corresponding activity of P. bryantii was more than 40-fold higher than in other strains. Zymogram analyses routinely detected the presence of high-molecular-weight (100–170 kDa) polysaccharide-degrading enzymes in ruminal Prevotella. Characteristics of the polysaccharide-degrading activities showed diversity of ruminal Prevotella species. Received: 29 November 1999 / Accepted: 1 February 2000     

Cleavage of di- and tripeptides by Prevotella ruminicola

The final step in the conversion of protein to amino acids by the common Gram-negative rumen bacterium, Prevotella (formerly Bacteroides) ruminicola , is the cleavage of di- and tripeptides. Dipeptidase and tripeptidase activities were predominantly cytoplasmic, and toluene treatment increased the rate of Ala₂ and Ala₃ hydrolysis by whole cells, suggesting that transport limited the rate of hydrolysis of extracellular di- and tripeptides. The hydrolysis of Ala₂ and Ala₃ by whole cells was not affected by protonophores, ionophores or dicyclohexylcarbodiimide, but Ala₂ hydrolysis by EDTA-treated cells was inhibited by the Ca²⁺/H⁺ ionophore, tetronasin. Ala₃ hydrolysis was not affected by protonophores or ionophores in EDTA-treated cells. The dipeptidase of strain M384 was inhibited > 99% by 1,10-phenanthroline and 39% by EDTA but not other protease inhibitors, consistent with the enzyme being a metalloprotease. Tripeptidase was insensitive to protease inhibitors, except for a 33% inhibition by EDTA. Cleavage of tripeptides occurred at the bond adjacent to the N-terminal amino acid. Distinct di-, tri- and oligopeptidase peaks were obtained by anion-exchange liquid chromatography of disrupted cells. Banding patterns on native PAGE using activity staining also indicated that P. ruminicola M384 had separate single dipeptidase and tripeptidase enzymes which hydrolysed a range of peptides. The dipeptidase of strain M384 was different from other strains of P. ruminicola: strains GA33 and B₁4 had activities which ran at the same R_f; strain GA33 had another band of lower activity; strain 23 had two bands different from those of the other strains. The tripeptidases ran at the same R_f for the different strains. Dipeptidase activity of all strains was inhibited by 1,10-phenanthroline on gels. Gel permeation chromatography indicated that the M_r of the dipeptidases from strains M384 and B₁4 were 115 000 and 114 500 respectively, and 112 500 and 121 500 for the corresponding tripeptidases. Thus the metabolism of small peptides by P. ruminicola involves separate permeases and intracellular peptidases for di- and tripeptides.     

Morphological study of five bacteriophages of yellow-pigmented enterobacteria

Two bacteriophages isolated onEnterobacter cloacae (C2, C2F) and three isolated onErwinia herbicola (E3, E16P, E16B) were purified by D₂O gradient centrifugation. Phage-containing fractions were negatively stained and examined by electron microscopy. Phages C2, C2F, E3, and E16P showed an elongated head 153×51 nm and a short noncontractile tail 12 nm long terminated by at least two short fibers. These phages correspond to the rate taxonomic group C3. Big capsomeres composing the phage head were evidenced when phage suspensions in D₂O were stained. Phage E16B showed an elongated head 97×40.5 nm, and a contractile tail 89 nm long. This phage corresponds to the extremely rate group A3.     

The Glucomannokinase of the Gram-Negative Ruminal Bacterium,Prevotella bryantii B14, and its Sequence Conservation with Regulatory Glucokinases of Gram-Positive Bacteria

The glucomannokinase gene of Prevotella bryantii B₁4, a strictly anaerobic ruminal bacterium, was amplified with degenerate PCR primers. The degenerate PCR primers were based on the N-terminal amino acid residues of the purified glucomannokinase and the C-terminus of other bacterial glucokinases. The PCR product had a molecular weight of approximately 550 bp. Because the purified glucomannokinase was composed of dimers with a monomer molecular weight of 34.5 kDa, the PCR product accounted for approximately 60% of the glucomannokinase DNA sequence. The B₁4 sequence had significant similarity with the glucokinases of several aerobic, Gram-positive bacteria (Streptomyces coelicolor,Staphylococcus xylosus , Bacillus subtilis, Bacillus megaterium). Previous work indicated that the Gram-positive glucokinases and the B₁4 glucomannokinase have a role in catabolite repression. These presumptive regulatory kinases formed a cluster that was distinct from other bacterial glucokinases. Amino acid sequence analyses indicated that the regulatory glucokinase genes (including the P. bryantii B₁4 glucomannokinase gene) had a mean sequence similarity of 42 ± 2.4%. The regulatory kinases had some highly conserved regions with other bacterial glucokinases, but the mean similarity was lower (17 ± 2.0%). The role of regulatory kinases in catabolite repression has not been precisely defined, but sequence comparisons suggest a common theme may exist. Because P. bryantii B₁4 is a Gram-negative bacterium, it appears that regulatory glucokinases may be widely distributed in eubacteria and not restricted to Gram-positive species.     

Variations in the Ability of Ruminal Gram-Negative Prevotella Species to Resist Monensin

Gram-negative, ruminal Prevotella strains (n = 15) differed greatly in their sensitivity to the feed additive monensin. Strains that were repeatedly transferred with sublethal doses tolerated more monensin than those that were unadapted, but growth experiments indicated that the sensitivity range was as great as 2000-fold. Prevotella bryantii B₁4 grew with monensin concentrations as high as 20 μM, but P. ruminicola H15a, D31d, 20-63, E40a, and D42f never initiated growth if monensin was greater than 0.01 μM. Washed cell preparations that were energized with glucose lost intracellular potassium when monensin was added, and potassium depletion could also be used as an index of monensin sensitivity. Adapted cells of P. bryantii B₁4 had a half-maximal potassium depletion constant (K _d) of 3.2 μM, but the K _d values of P. ruminicola strains H15a, D31d, 20-63, E40a, and D42f were less than 0.04 μM. Maximal potassium depletion (K _max) values range from 90% to 40%, and monensin-adapted cells always had lower K _max values than unadapted cells. A linear regression of log K _d/K _max versus percentage decrease in optical density divided by monensin concentration had an r² of 0.75, and this regression indicated that potassium depletion from washed cells closely correlated with growth inhibition. P. bryantii B₁4 had a K _d/K _max ratio that was sevenfold greater than other Prevotella strains, and this result indicated that P. bryantii may be unusual in its ability to grow with very high concentrations of monensin. Received: 13 August 1999 / Accepted: 5 October 1999     

Formate utilization by members of the genus Methanobacterium

Washed cell suspensions of Methanobacterium formicicum MF, Methanobacterium bryantii M.o.H.G. and Methanobacterium strain FR-2 but not Methanobacterium bryantii M.o.H., were shown to produce hydrogen and methane from formate. Levels of dissolved gases (H₂ and CH₄) were continuously and simultaneously monitored within a closed reaction vessel using membrane inlet mass spectrometry. Growth on formate (0–50mM), measured by methane production and increase in absorbance, was observed for both M. formicicum MF and M. bryantii M.o.H.G. but not with Methanobacterium strain FR-2 or M. bryantii M.o.H.     

Bioinformatic evidence and characterization of novel putative large conjugative transposons residing in genomes of genera <Emphasis Type="Italic">Bacteroides</Emphasis> and <Emphasis Type="Italic">Prevotella</Emphasis>

Bioinformatic evidence of the presence of a large conjugative transposon in ruminal bacterium Prevotella bryantii B₁4^T is presented. The described transposon appears to be related to another large conjugative transposon CTnBST, described in Bacteroides uniformis WH207 and to the conjugative transposon CTn3-Bf, which was observed in the genome of Bacteroides fragilis strain YCH46. All three transposons share tra gene regions with high amino acid identity and clearly conserved gene order. Additionally, a second conserved region consisting of hypothetical genes was discovered in all three transposons and named the GG region. This region served as a specific sequence signature and made possible the discovery of several other apparently related hypothetical conjugative transposons in bacteria from the genus Bacteroides. A cluster of genes involved in sugar utilization and metabolism was discovered within the hypothetical CTnB₁4, to a certain extent resembling the polysaccharide utilization loci which were described recently in some Bacteroides strains. This is the first firm report on the presence of a large mobile genetic element in any strain from the genus Prevotella.     

Bacterial host strains that support replication of somatic coliphages

Somatic coliphages detected by Escherichia coli strain WG5 have been proposed as potential indicators of water quality. Their potential replication in the water environment is considered a drawback for their use as indicators. However, the contribution of replication outside the gut to the total numbers has never been quantified. It has not been determined either the fraction of bacterial strains that might support replication of phages detected by strain WG5 in the water environment. We examined the sensitivity of 291 host strains to 25 phages by streaking slants of the presumptive host strain onto an agar layer that contains bacteriophages, which gives a total of 7275 combinations (sensitivity tests). Only a 3.02% of the tests showed sensitivity. Additionally, six environmental strains were used as hosts to count phages in sewage and seawater. Phages isolated on these strains were used to infect strain WG5. The environmental strains detected 1 log₁₀ fewer phages than strain WG5 in sewage and seawater. The fraction of phages that were detected by the six strains and that also infected strain WG5 ranged from < 0.07% to < 2.0% of the total amount of bacteriophages detected by strain WG5 in the same samples. Our results confirm that less than 3% of naturally occurring hosts support replication of phages infecting E. coli. We conclude that the contribution of replication to the number of somatic coliphages detected in the aquatic environment is negligible. This revised version was published online in June 2006 with corrections to the Cover Date.     

Bacterial growth rate and growth pouch nodulation profile differences as possible ways of Bradyrhizobium japonicum strain screening for low P soils

This work studied the effects of P fertilization on nodulation of field-grown soybean by two Bradyrhizobium strains (SMGS₁ and THA₇), and checked if differences between strains were consistent with bacterial growth and growth pouch nodulation ability in response to P availability. In the field, nodule dry weight and nitrogen fixation activity of inoculated soybean were studied on typical acid soils of Thaïland at the flowering (R₁) stage and at the end of grain filling. Grain yield, growth and phosphorus content were recorded. The bradyrhizobial strains were cultivated in culture medium, and growth parameters recorded. Nodulation patterns were observed during growth pouch experiments: infective root cells were inoculated with strains cultivated at two P concentrations in their culture media, namely 1 M and 1 mM. Ten days after inoculation, the position of each nodule was measured relative to the root tip (RT) mark, expressed relative to the smallest emerging root hairs-RT distance in the nodulation frequency profile, and the consistency of responses was tested. In the field, on P deficient soils, dry weight of nodules was higher with Bradyrhizobium japonicum strain SMGS₁ than with strain THA₇. P supply increased the number and dry weight of nodules for both strains, with a higher dry weight response for THA₇ than for SMGS₁. It also had a positive effect on tissue phosphorus status and grain yield at R₈ stage. In growth media, significant differences were recorded between strains under P-limiting conditions: The growth rate was higher for strain SMGS₁, as well as the maximal number of bacterial cells supported. With growth pouch, inoculating plants with bacteria grown in P-deficient medium resulted in a less intense nodulation of roots by THA₇, and with nodules appearing earlier on roots than in the case of SMGS₁. At 1 mM P, there was no significant difference between strains. Thus, strain THA₇ is more affected by P deficiency than strain SMGS₁. Although P was not supplied in the same way in the soil and in the growth pouch experiments, this consistency of behaviour between work scales indicates that phosphorus availability is a key component for a successful inoculation. Furthermore, the study of bacterial growth rates and nodulation profile represents an interesting step for bacterial screening for low P soils. [-11pt]     

明永冰川融水中一株裂解性低温噬菌体的分离及特征

【目的】高山冰川是一类独特的生态系统,本研究探索从明永冰川地区分离和培养低温菌噬菌体,并对其特征进行研究。【方法】利用已分离的低温菌为宿主,采用"双层平板法"从明永冰川融水中分离纯化低温菌噬菌体;对噬菌体及其宿主进行电镜形态观察,并进行噬菌体基因组限制性酶切片段长度多态性分析、衣壳蛋白组成分析及噬菌体生理特征研究。【结果】从明永冰川融水中分离获得一株裂解性低温噬菌体,命名为MYSP03(Mingyong Flavobacterium Siphoviridae Bacteriophage),其宿主菌MYB03鉴定为Flavobacterium菌株。噬菌体MYSP03为长尾型,无囊膜,头部具典型的正多面体立体对称结构,直径约72 nm;尾管长约240 nm,直径约10 nm;4℃时具侵染活性,在4℃-20℃范围内均可产生边缘清晰、透明的噬菌斑,最适感染温度约10℃,pH耐受范围较广,最适感染pH约9.4,对氯仿不敏感,基因组为双链DNA,大小约66 kb。     

Phages C-2 and J: IncC and IncJ plasmid-dependent phages, respectively

Phages C-2 and J were isolated from sewage. Phage C-2 was filamentous and formed plaques on Salmonella typhimurium strains carrying various C plasmids. It also plated on Proteus mirabilis and Serratia marcescens strains carrying particular C plasmids, but failed to form plaques on lines of Escherichia coli K12 strains harbouring most of these plasmids, although in all cases, phage multiplication on the strains was demonstrated. No phage increase occurred in any strain which lacked a C plasmid or contained plasmids of other incompatibility groups. The phage was sensitive to chloroform and, unlike other filamentous bacterial viruses, adsorbed to shafts of conjugative pili. It had a disc-like structure at the end which attached to the pilus. Phage C-2 had a buoyant density of 1 . 30 g cm-3 and a single-stranded circular DNA genome of 3 . 0 MDal. Phage J had an hexagonal head with an inter-apical distance of 40 nm and a short noncontractile tail. It was resistant to chloroform and diethyl ether. The phage formed plaques or propagated on E. coli strains harbouring some IncC plasmids and all IncJ and IncD plasmids tested. The phage did not form plaques but propagated on P. mirabilis and Ser. marcescens strains carrying these plasmids. It did not plate or propagate on S. typhimurium strains harbouring the plasmids. The plaques were very hazy and variable in size. The phage attached sparsely, at a site which appeared to be located at the base of the tail, to sides of conjugative pili.     

Bacteriophages drive strain diversification in a marine Flavobacterium: implications for phage resistance and physiological properties

Genetic, structural and physiological differences between strains of the marine bacterium Cellulophaga baltica MM#3 (Flavobacteriaceae) developing in response to the activity of two virulent bacteriophages, ΦS_M and ΦS_T, was investigated during 3 weeks incubation in chemostat cultures. A distinct strain succession towards increased phage resistance and a diversification of the metabolic properties was observed. During the incubation the bacterial population diversified from a single strain, which was sensitive to 24 tested Cellulophaga phages, into a multistrain and multiresistant population, where the dominant strains had lost susceptibility to up to 22 of the tested phages. By the end of the experiment the cultures reached a quasi steady state dominated by ΦS_T‐resistant and ΦS_M + ΦS_T‐resistant strains coexisting with small populations of phage‐sensitive strains sustaining both phages at densities of > 10⁶ plaque forming units (pfu) ml^?1. Loss of susceptibility to phage infection was associated with a reduction in the strains' ability to metabolize various carbon sources as demonstrated by BIOLOG assays. This suggested a cost of resistance in terms of reduced physiological capacity. However, there was no direct correlation between the degree of resistance and the loss of metabolic properties, suggesting either the occurrence of compensatory mutations in successful strains or that the cost of resistance in some strains was associated with properties not resolved by the BIOLOG assay. The study represents the first direct demonstration of phage‐driven generation of functional diversity within a marine bacterial host population with significant implications for both phage susceptibility and physiological properties. We propose, therefore, that phage‐mediated selection for resistant strains contributes significantly to the extensive microdiversity observed within specific bacterial species in marine environments.     

Growth promotion of Chlorella ellipsoidea by co-inoculation with Brevundimonas sp. isolated from the microalga

Eight bacterial strains identified as P1, P2, Y1, Y2, W1, W2, G, and R were isolated from a long-term laboratory culture of the green alga Chlorella ellipsoidea. Although it is unknown how these bacterial strains have been maintained with the C. ellipsoidea culture, all appeared to promote the growth of C. ellipsoidea. Co-inoculation of each bacterial strain with C. ellipsoidea resulted in 0.5–3 times greater algal growth than that of C. ellipsoidea alone. The most effective bacterium (i.e., strain P1) was selected and further characterized. Biochemical analysis and transmission electron microscopy revealed that strain P1 is closely related to the genus Brevundimonas. Sequence analysis of the 16S rRNA of strain P1 showed 99.9 and 99.4% nucleotide sequence identity to that of B. nasdae and B. vesicularis, respectively. In addition to the growth promotion of C. ellipsoidea by strain P1, the growth of strain P1 was also significantly enhanced by co-culturing with C. ellipsoidea, indicating a symbiotic relationship between the bacterium and alga. Scanning electron microscopy showed the direct adhesion of strain P1 cells to the surface of C. ellipsoidea cells, as well as the development of abundant crinkles on the surface of co-cultured C. ellipsoidea cells. Handling editor: J. Padisak     

BVPaP-3, a T7-Like Lytic Phage of <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis>: Its Isolation and Characterisation

The increasing emergence of antibiotic-resistant bacteria has produced a growing interest among scientists in bacteriophages as alternative antimicrobial agents. This article reports a lytic phage against an antibiotic-resistant strain of Pseudomonas aeruginosa. Phage BVPaP-3 is a member of the Podoviridae family and morphologically similar to the T7-like phage gh-1. The phage has a hexagonal head of 58–59 nm in diameter and a short tail of 10 × 8 nm. It is stable at a wide range of pH (6–10) and temperatures (4–40°C). Its optimal growth temperature is 37°C and the adsorption rate constant is 1.19 × 10⁻⁹. Latent and eclipse periods are 20 and 15 min, respectively, and the burst size is 44 after 35 min at 37°C. The phage has a DNA size of 41.31 kb and a proteome of 11 proteins. The major protein is 33 kDa in size.