Novel L-amino acid oxidase with algicidal activity against toxic cyanobacterium Microcystis aeruginosa synthesized by a bacterium Aquimarina sp

A brownish yellow pigmented bacterial strain, designated antisso-27, was recently isolated from a water area of saltpan in Southern Taiwan. Phylogenetic analyses based on 16S rRNA gene sequences indicate that strain antisso-27 belongs the genus Aquimarina in the family Flavobacteriacea and its only closest neighbor is Aquimarina spongiae (96.6%). Based on screening for algicidal activity, strain antisso-27 exhibits potent activity against the toxic cyanobacterium Microcystis aeruginosa. Both the strain antisso-27 bacterial culture and its culture filtrate show algicidal activity against the toxic cyanobacterium, indicating that an algicidal substance is released from strain antisso-27. The algicidal activity of strain antisso-27 occurs during the late stationary phase of bacterial growth. Strain antisso-27 can synthesize an algicidal protein with a molecular mass of 190 kDa, and its isoelectric point is approximately 9.4. This study explores the nature of this algicidal protein such as l-amino acid oxidase with broad substrate specificity. The enzyme is most active with l-leucine, l-isoleucine, l-methionine and l-valine and the hydrogen peroxide generated by its catalysis mediates algicidal activity. This is the first report on an Aquimarina strain algicidal to the toxic M. aeruginosa and the algicidal activity is generated through its enzymatic activity of l-amino acid oxidase.     

Characterization of an algicidal bacterium Brevundimonas J4 and chemical defense of Synechococcus sp. BN60 against bacterium J4

As part of efforts to enhance the strategies explored to eliminate the adverse impacts of cyanobacterial blooms, we isolated an algicidal bacterium, J4, from Lake Taihu. Analysis of 16S rDNA sequence revealed that strain J4 belonged to the genus Brevundimonas. Bacterium J4 exhibited algicidal activity mainly through excretion of extracellular algicidal compounds that were further extracted with methanol and purified by silica gel chromatography and high performance liquid chromatography (HPLC). The compounds showed thermal stability, strong polarity and water solubility in J4 cultures. Study on the algicidal activity of J4 against two dominant cyanobacterial bloom-forming species in Lake Taihu showed that J4 exhibited lower algicidal rate against Synechococcus sp. BN60 (48.6%, t = 6 days) than against Microcystis aeruginosa 9110 (91.8%, t = 6 days). Additionally, rapid reduction in cell density of J4 was observed in co-cultures of Synechococcus sp. BN60 and bacterium J4 but not observed in co-cultures of M. aeruginosa 9110 and bacterium J4 during algicidal process, which was the main reason why the algicidal rate of J4 against BN60 was lower than against 9110. The reduction in cell density of J4 resulted from inducible production of antimicrobial-like compound secreted by Synechococcus sp. BN60 in co-cultures of Synechococcus sp. BN60 and bacterium J4, which reflected a kind of chemical defense from cyanobacteria (BN60) against algicidal bacteria (J4). However, M. aeruginosa 9110 had no chemical defense against J4, suggesting that whether cyanobacterial chemical defense occurs or not between cyanobacteria and algicidal bacteria depends on specific cyanobacteria–algicidal bacteria pairs. These results show that not only one-sided algicidal effect but also two-sided reciprocal inhibition interactions exist between algicidal bacteria and cyanobacteria, indicating the complexity of cyanobacteria–algicidal bacteria interactions in Lake Taihu and the need to take the cyanobacterial defensive responses into consideration when assessing potential use of algicidal bacteria.     

A freshwater bacterial strain,Shewanella sp. Lzh-2, isolated from Lake Taihu and its two algicidal active substances,hexahydropyrrolo[1,2-a]pyrazine-1,4-dione and 2, 3-indolinedione

Cyanobacterial blooms have become a serious problem in Lake Taihu during the last 20 years, and Microcystis aeruginosa and Synechococcus sp. are the two dominant species in cyanobacterial blooms of Lake Taihu. A freshwater bacterial strain, Shewanella sp. Lzh-2, with strong algicidal properties against harmful cyanobacteria was isolated from Lake Taihu. Two substances with algicidal activity secreted extracellularly by Shewanella sp. Lzh-2, S-2A and S-2B, were purified from the bacterial culture of strain Lzh-2 using ethyl acetate extraction, column chromatography, and high performance liquid chromatography (HPLC) in turn. The substances S-2A and S-2B were identified as hexahydropyrrolo[1,2-a]pyrazine-1,4-dione and 2, 3-indolinedione (isatin), respectively, based on liquid chromatography-mass spectrometry (LC-MS), gas chromatography-mass spectrometry (GC-MS), and hydrogen-nuclear magnetic resonance (H-NMR) analyses, making this the first report of their algicidal activity toward cyanobacteria. S-2A (hexahydropyrrolo[1,2-a]pyrazine-1,4-dione) had no algicidal effects against Synechococcus sp. BN60, but had a high level of algicidal activity against M. aeruginosa 9110. The LD50 value of S-2A against M. aeruginosa 9110 was 5.7 μg/ml. S-2B (2, 3-indolinedione) showed a potent algicidal effect against both M. aeruginosa 9110 and Synechococcus sp. BN60, and the LD50 value of S-2B against M. aeruginosa 9110 and Synechococcus sp. BN60 was 12.5 and 34.2 μg/ml, respectively. Obvious morphological changes in M. aeruginosa 9110 and Synechococcus sp. BN60 were observed after they were exposed to S-2A (or S-2B) for 24 h. Approximately, the algicidal activity, the concentration of S-2A and S-2B, and the cell density of Lzh-2 were positively related to each other during the cocultivation process. Overall, these findings increase our knowledge about algicidal substances secreted by algicidal bacteria and indicate that strain Lzh-2 and its two algicidal substances have the potential for use as a bio-agent in controlling cyanobacterial blooms in Lake Taihu.     

Wheat Bran Enhances the Cytotoxicity of Immobilized Alcaligenes aquatilis F8 against Microcystis aeruginosa

Algicidal bacteria offer a promising option for killing cyanobacteria. Therefore, a new Alcaligenes aquatilis strain F8 was isolated to control Microcystis aeruginosa in this study. The algicidal activity of strain F8 was dependent on the cell density of M. aeruginosa, and the maximal algicidal rate of the free bacterium reached 88.45% within 72 h. With a view to its application to the control of M. aeruginosa in the natural environment, strain F8 was immobilized in sodium alginate beads, but immobilization of the strain decreased its algicidal rate compared to that of the free bacterium. However, addition of wheat bran to the sodium alginate matrix used to immobilize strain F8 not only eliminated the adverse effects of immobilization on the bacteria but also resulted in an 8.83% higher algicidal rate of the immobilized than free bacteria. Exclusion and recovery methods were used to identify key ingredients of wheat bran and gain insight into the mechanism underlying the observed enhancement of algicidal activity. This analysis indicated that certain factors in wheat bran, including vitamins B₁, B₂, B₉, and E were responsible for promoting bacterial growth and thereby improving the algicidal rate of immobilized strain F8. Our findings indicate that wheat bran is able to improve the algicidal efficiency of A. aquatilis strain F8 for killing M. aeruginosa and is a good source of not only carbon and nitrogen but also vitamins for bacteria.     

Growth inhibition of unicellular and colonial Microcystis strains (Cyanophyceae) by compounds isolated from rice (Oryza sativa) hulls

The algicidal effects of crude and pure rice hull extracts on the growth of Microcystis aeruginosa were investigated using cultured unicellular and colonial strains. Upon treatment with rice hull crude extract (RHE), growth inhibition of unicellular M. aeruginosa was much higher than that of colonial M. aeruginosa. However, purified compounds from the crude extract, β-sitosterol-β-d-glucoside and dicyclohexanyl orizane, powerfully inhibited the growth of colonial M. aeruginosa cells. At the same concentrations, the two compounds were almost equipotent (66% and 80% growth inhibition for colonial M. aeruginosa, respectively; P < 0.05). As rice hulls are readily obtainable, and as extracts show high algicidal activity (targeting colonial algae rather than unicellular organisms) at low concentrations, the results suggest that some pure compounds extracted from rice hulls, such as β-sitosterol-β-d-glucoside and dicyclohexanyl orizane, may serve as environmentally friendly agents for controlling the growth of toxic colonial M. aeruginosa in eutrophic waters.     

Isolation and algicidal characterization of <Emphasis Type="Italic">Bowmanella denitrificans</Emphasis> S088 against <Emphasis Type="Italic">Chlorella vulgaris</Emphasis>

One strain of algicidal bacterium, named as S088, was isolated from the intestine of healthy sea cucumbers (Stichopus horrens) in the South China Sea. Based on the analysis of its biochemical characteristics and 16S rDNA gene sequence, S088 was identified as Bowmanella denitrificans. Importantly, the algicidal activity of S088 on Chlorella vulgaris was characterized in this study. The initial densities of bacterial and algal cell showed strong influence on the removal rates of chlorophyll a. When the strain S088 was cultured under a complete darkness condition at 30 °C, its algicidal activity reached the highest level. Furthermore, it was found that the filtered supernatant from bacterial cultures had full algicidal activity, suggesting that the secreted compounds from S088 are involved in the observed algicidal action of S088. Moreover, the algicidal compounds were heat tolerant and had no cytotoxicity against fish cells, indicating that S088 would have a promising application as a safe probiotics for S. horrens. Finally, this is the first report about the algicidal activities in B. denitrificans.     

The potential use of bacterium strain R219 for controlling of the bloom-forming cyanobacteria in freshwater lake

Cyanobacterial blooms become a serious environmental threat to the freshwater ecosystem, and several physical and chemical methods have been developed for controlling the blooms. In order to develop a biocontrol agent for controlling the blooms, we isolated a bacterial strain R219 that exhibited strong algicidal activity against the dominant bloom-forming species of Microcystis aeruginosa from Lake Tai in China. Based on 16S rDNA sequence analysis we determined the strain R219 to be Pseudomonas aeruginosa by the virtue of its sharing about 99.8% similarity with reference strains in the DNA databases. Biochemical and morphological tests were used to support the accurate identification as that of the bacterium P. aeruginosa. We also tested culture filtrate and ethyl acetate extract of strain R219 and showed both of them exhibited strong algicidal effect on the growth of M. aeruginosa at mid-exponential phase when the R219 filtrate and ethyl acetate extract were applied at various cell densities. Moreover, the P. aeruginosa filtrate showed high potency in removal of the mixed species bloom-forming cyanobacteria collected directly from the Lake Tai. When adding the filtrate of the strain R219 to the mixed-species cyanobacteria, the content of chlorophyll-a of the algae were reduced by as much as 80–90%. Oral acute toxicity assessment for strain R219 demonstrated that all the mice that received the broth or filtrate in doses of 0.5 or 2.0 g kg^?1 were alive without any immediate behavioral changes within 14 days of administration of either broth or filtrate. These results indicate that the strain R219 may have potential for a use in controlling the bloom-forming cyanobacteria in freshwater ecosystems.     

Toxic Effect of a Marine Bacterium on Aquatic Organisms and Its Algicidal Substances against Phaeocystis globosa

Harmful algal blooms have caused enormous damage to the marine ecosystem and the coastal economy in China. In this paper, a bacterial strain B1, which had strong algicidal activity against Phaeocystis globosa, was isolated from the coastal waters of Zhuhai in China. The strain B1 was identified as Bacillus sp. on the basis of 16S rDNA gene sequence and morphological characteristics. To evaluate the ecological safety of the algicidal substances produced by strain B1, their toxic effects on marine organisms were tested. Results showed that there were no adverse effects observed in the growth of Chlorella vulgaris, Chaetoceros muelleri, and Isochrystis galbana after exposure to the algicidal substances at a concentration of 1.0% (v/v) for 96 h. The 48h LC₅₀ values for Brachionus plicatilis, Moina mongolica Daday and Paralichthys olivaceus were 5.7, 9.0 and 12.1% (v/v), respectively. Subsequently, the algicidal substances from strain B1 culture were isolated and purified by silica gel column, Sephadex G-15 column and high-performance liquid chromatography. Based on quadrupole time-of-flight mass spectrometry and PeakView Software, the purified substances were identified as prolyl-methionine and hypoxanthine. Algicidal mechanism indicated that prolyl-methionine and hypoxanthine inhibited the growth of P. globosa by disrupting the antioxidant systems. In the acute toxicity assessment using M. mongolica, 24h LC₅₀ values of prolyl-methionine and hypoxanthine were 7.0 and 13.8 g/L, respectively. The active substances produced by strain B1 can be considered as ecologically and environmentally biological agents for controlling harmful algal blooms.     

Novel algicidal evidence of a bacterium Bacillus sp. LP-10 killing Phaeocystis globosa,a harmful algal bloom causing species

While searching for effective bio-agents to control harmful algal blooms (HABs), the bacterial strain LP-10, which has strong algicidal activity against Phaeocystis globosa (Prymnesiophyceae), was isolated from surface seawater samples taken from the East China Sea. 16S rDNA sequence analysis and morphological characteristics revealed the strain LP-10 belonged to the genus Bacillus. The lytic effect of Bacillus sp. LP-10 against P. globosa was both concentration- and time-dependent. Algicidal activities of different growth stages of the bacterial culture varied significantly. The lytic effect of different parts of the bacterial cultures indicated that the algal cells were lysed by algicidal active compounds in the cell-free filtrate. Analysis of the properties of the active compounds showed that they had a molecular weight of less than 1000 Da and that the active compounds were stable between −80 and 121 °C. The algicidal range assay indicated that five other algal species were also suppressed by strain LP-10, including: Alexandrium catenella, A. tamarense, A. minutum, Prorocentrum micans and Asterionella japonica. Our results suggested that the algicidal bacterium Bacillus sp. LP-10 could be a potential bio-agent to control the blooms of harmful algal species.     

Isolation and Identification of Algicidal Compound from Streptomyces and Algicidal Mechanism to Microcystis aeruginosa

The biological control of cyanobacterial harmful algal blooms (cyanoHABs) is important to promote human health, environmental protection, and economic growth. Active algicidal compounds and algicidal mechanisms should be identified and investigated to control cyanoHABs. In this study, the algicidal actinobacterium Streptomyces sp. L74 was isolated from the soil of a nearby pond which located in the center lake of Guanghzou Higher Education Mega Center. Results showed that the algicidal activities of cyanoHABs are mainly achieved via an indirect attack by producing algicidal compounds. All active algicidal compounds are hydrophilic substances that are heat and pH stable. In the present study, an active compound (B3) was isolated and purified by high-performance liquid chromatography and identified as a type of triterpenoid saponin (2-hydroxy-12-oleanene-3, 28-O-D-glucopyranosyl) with a molecular formula of C₄₂H₇₀O₁₃ as determined by infrared spectrometry, electrospray ionization mass spectrometry, and nuclear magnetic resonance. Active algicidal compounds from Streptomyces sp. L74 were shown to disrupt the antioxidant systems of Microcystis aeruginosa cells.     

Algicidal Effects of a Novel Marine Actinomycete on the Toxic Dinoflagellate <Emphasis Type="Italic">Alexandrium tamarense</Emphasis>

A marine actinomycete strain BS01 with algicidal activity to the toxic dinoflagellate, Alexandrium tamarense, was isolated from Xiamen Bay, China. Sequence analysis of 16S rDNA demonstrates that BS01 is closely related to the genus Brevibacterium of Actinomycetales. BS01 exhibited algicidal activity in an indirect manner. Additional organic nutrients, but not algal-derived dissolved organic matter, were necessary for the synthesis of yet unidentified algicidal compounds (molecular weight less than 100), which were heat tolerant, a stable in acidic or alkali conditions, and exhibited a wide range of algicidal activity. This is the first report of an actinomycete algicide to the toxic dinoflagellate A. tamarense. Our results indicate that BS01 could be a potential bio-agent for controlling harmful algal blooms.     

Marine bacteria antagonistic to the harmful algal bloom species Alexandrium tamarense (Dinophyceae)

As part of efforts to enhance the strategies employed to manage and mitigate algal blooms and their adverse effects, algicidal bacteria have shown promise as potential suppressors of these events. Nine strains of bacteria algicidal against the toxic dinoflagellate, Alexandrium tamarense, were isolated from the East Sea area, China. Sequence analysis of 16S rDNA showed that all the algicidal bacteria belonged to the γ-proteobacteria subclass and the genera Pseudoalteromonas (strain SP31 and SP44), Alteromonas (strain DH12 and DH46), Idiomarina (strain SP96), Vibrio (strain DH47 and DH51) and Halomonas (strain DH74 and DH77). To assess the algicidal mode of these algicidal bacteria, bacterial cells and the filtrate from bacterial cultures were inoculated into A. tamarense cultures, and fluorescein diacetate vital stain was applied to monitor the growth of the algal cells. The results showed that all the algicidal bacteria exhibited algicidal activity through an indirect attack since algicidal activity was only detected in cell free supernatants but not the bacterial cells. This is the first report of bacteria from the genus Idiomarina showing algicidal activity to the toxic dinoflagellate A. tamarense and these findings would increase our knowledge of bacterial–algal interactions and the role of bacteria during the population dynamics of HABs.     

Involvement of an Extracellular Protease in Algicidal Activity of the Marine Bacterium Pseudoalteromonas sp. Strain A28

The marine bacterium Pseudoalteromonas sp. strain A28 was able to kill the diatom Skeletonema costatum strain NIES-324. The culture supernatant of strain A28 showed potent algicidal activity when it was applied to a paper disk placed on a lawn of S. costatum NIES-324. The condensed supernatant, which was prepared by subjecting the A28 culture supernatant to ultrafiltration with a 10,000-M_w-cutoff membrane, showed algicidal activity, suggesting that strain A28 produced extracellular substances capable of killing S. costatum cells. The condensed supernatant was then found to have protease and DNase activities. Two Pseudoalteromonas mutants lacking algicidal activity, designated NH1 and NH2, were selected after N-methyl-N′-nitrosoguanidine mutagenesis. The culture supernatants of NH1 and NH2 showed less than 15% of the protease activity detected with the parental strain, A28. The protease was purified to homogeneity from A28 culture supernatants by using ion-exchange chromatography followed by preparative gel electrophoresis. Paper-disk assays revealed that the purified protease had potent algicidal activity. The purified protease had a molecular mass for 50 kDa, and the N-terminal amino acid sequence was determined to be Ala-Thr-Pro-Asn-Asp-Pro. The optimum pH and temperature of the protease were found to be 8.8 and 30°C, respectively, by using succinyl-Ala-Ala-Pro-Phe-p-nitroanilide as a substrate. The protease activity was strongly inhibited by phenylmethylsulfonyl fluoride, diisopropyl fluorophosphate, antipain, chymostatin, and leupeptin. No significant inhibition was detected with EDTA, EGTA, phenanthroline or tetraethylenepentamine. These results suggest that Pseudoalteromonas sp. strain A28 produced an extracellular serine protease which was responsible for the algicidal activity of this marine bacterium.     

Extracellular lipase from <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> JCM5962(T): Isolation,identification, and characterization

The study was done to isolate, identify, and characterize a good lipolytic strain from soil. Lipolytic strain isolation was done using tributyrin agar medium. The biochemical testing and 16S rRNA gene sequencing analysis was done for identification. The enzyme was purified using ammonium sulfate precipitation and column chromatography. Results have shown a novel high lipolytic strain of P. aeruginosa JCM5962(T), isolated from soil of sugarcane field. The 16S rRNA sequence analysis confirmed the strain as P. aeruginosa JCM5962(T); further, the sequence was submitted to Genbank (KX946966.1). The isolate produced an extracellular lipase which was purified as single band of 31 kDa. Maximum lipase activity was observed at 50 °C and pH 8.0. Activity was enhanced in the presence of cobalt and benzene solvent, whereas mercury, sodium dodecyl sulfate, and chloroform inhibited it. The enzyme’s marked stability and activity at high temperature, alkaline pH and organic solvents suggest that this can be effectively used in a variety of applications in industries and as biotechnological tools.     

Enhanced species-specific chemical control of harmful and non-harmful algal bloom species by the thiazolidinedione derivative TD49

Culture experiments involving 23 algae strains were conducted to evaluate the algicidal effects of a newly developed algicidal thiazolidinedione (TD) derivative (TD49) on non-harmful and harmful algal bloom (HAB) species. We also assessed the effect of various concentrations of TD49 on various growth phases (lag, logarithmic, and stationary) of the harmful algae Heterocapsa circularisquama (Dinophyceae) and Heterosigma akashiwo (Raphidophyceae; hereafter, Heterosigma) and the non-harmful diatoms Skeletonema costatum and Chaetoceros didymus. The inhibitory ratios (%) for H. circularisquama and Heterosigma at 2.0 μM TD49 were significantly higher than those at other concentrations, and the inhibitory ratio varied depending on growth phase and species as follows: logarithmic?≥?stationary?>?lag phase for H. circularisquama and logarithmic?≥?lag?>?stationary phase for Heterosigma. Although the inhibitory ratios for C. didymus were similar to those for the two harmful algae (H. circularisquama and Heterosigma), inhibitory effects on S. costatum were not apparent at >2.0 μM in any growth phase. The algicidal activity of TD49 on the harmful and non-harmful algae was as follows: unarmored HAB species?>?armored HAB species?>?diatom species?>?cryptophyte species. TD49 was algicidal to most HABs but had a little inhibitory effect on some non-harmful algae, implying that TD49 has selective algicidal activity. Our results indicate that TD49 is potentially of use in the control of HAB species within semi-enclosed bays.     

Dynamics of cyanophage-like particles and algicidal bacteria causing Microcystis aeruginosa mortality

The dynamics of cyanophage-like particles and algicidal bacteria that infect the bloom-forming cyanobacterium Microcystis aeruginosa was followed in a hyper-eutrophic pond from September 1998 to August 1999. The densities of M. aeruginosa ranged between 4.0 × 10⁵ and 1.9 × 10⁷ cells ml⁻¹, whereas those of algicidal bacteria were between 4.0 and 5.1 × 10² plaque-forming units (PFU) ml⁻¹ and those of cyanophage-like particles were between <5.0 × 10² and 7.1 × 10³ PFU ml⁻¹. A significant relationship was found between the densities of algicidal bacteria and M. aeruginosa (r = 0.81, n = 69, P < 0.001), suggesting that the dynamics of the algicidal bacteria may regulate the abundance of M. aeruginosa. Occasional peaks of density of cyanophage-like particles were detected in October, June, and August, when sharp declines in M. aeruginosa cell densities were also observed. The densities of cyanophage-like particles became undetectable when the abundance of M. aeruginosa was low, suggesting the density-dependent infection of M. aeruginosa by cyanophage-like particles. Thus, we suggest that infections of both algicidal bacteria and cyanophage-like particles are important biological agents that decompose blooms of M. aeruginosa in freshwater environments. Received: August 31, 2000 / Accepted: December 6, 2000     

Complete genome sequence of plant growth promoting Pseudomonas aeruginosa AJ D 2 an isolate from monocropic cotton rhizosphere

A plant growth promoting Pseudomonas aeruginosa AJD 2 was isolated from monocropic cotton rhizosphere of Maharashtra state, India. The strain was identified as per physiological, biochemical and 16S rRNA gene sequencing (Accession number MG234531). The strain possess multiple functional plant growth promoting traits and antifungal activity. The genome was extracted, purified and library of avg.515 bp was prepared and sequenced by over Illumina platform. The sequenced genome was studied by using CLC workbench and NCBI pipeline using Pseudomonas aeruginosa PAO1 and Pseudomonas aeruginosa YL84 as reference assembler. The size of the genome is 6.1 Mb with 5802 genes within it. The study over strain may give an insight into its plant growth promotion mechanism.     

Isolation and partial characterization of antimicrobial compounds from a new strain <Emphasis Type="Italic">Nonomuraea</Emphasis> sp. NM94

An actinomycete strain NM94 was isolated from a Saharan soil sample by a dilution agar plating method using chitin-vitamins B medium supplemented with penicillin. The strain presented the morphological and chemical characteristics of the genus Nonomuraea. On the basis of 16S rDNA analysis and physiological tests, this isolate was found to be quite different from the known species of Nonomuraea and might be new. The strain NM94 secreted several antibiotics on yeast extract malt extract glucose medium that were active against some Gram-positive bacteria, yeast, and fungi. The antibiotics were extracted with dichloromethane and detected by bioautography on silica gel plates using Mucor ramannianus and Bacillus subtilis as the test organisms. Among these antibiotics, a complex called 94A showed interesting antifungal activity. It was selected and purified by reverse-phase HPLC. This complex was composed of five compounds. Spectroscopic studies by infrared, mass, and ¹H NMR of the compounds were carried out. Initial results showed that these molecules differed from the known antibiotics produced by other Nonomuraea species.     

Protective activities of ribosomal ribonucleic acid and lipopolysaccharide of Pseudomonas aeruginosa: a comparative study

Ribosomal ribonucleic acid (RNA) and lipopolysaccharide (LPS) from P. aeruginosa were compared with respect to their protective activities in mice against an infection with P. aeruginosa. This study is concentrated on the protective activity of RNA. RNA isolated from purified ribosomes did not contain LPS as determined with the Limulus test. Injection of RNA with the adjuvant dimethyldioctadecylammonium bromide (DDA) protected mice against P. aeruginosa without inducing LPS-specific antibodies. C₃H/HeJ mice which are relatively insensitive to the protective activity of LPS could be protected with RNA. The protective activities of RNA and LPS from a mutant strain of P. aeruginosa, PAC 605, containing defective lipopolysaccharide, were compared with the protective activities of RNA and LPS from the parent strain, PAC IR. The protective activity of LPS from PAC 605 was 1000 fold lower than the protective activity of LPS from PAC IR. RNA preparations of both strains induced similar percentages of survival. The protective activity of ribosomal RNA from P. aeruginosa was nonspecific since mice were also protected against a heterologous serotype of P. aeruginosa and against Escherichia coli. RNA from ribosomes of P. aeruginosa, E. coli and the non-lipopolysaccharide containing Saccharomyces cerevisiae had similar protective activities. No protection was obtained with the ribonucleic acid from the E. coli phage MS 2. It is concluded that ribosomal RNA has protective activities distinct from those of LPS.     

Isolation,identification, and algicidal activity of marine bacteria against <Emphasis Type="Italic">Cochlodinium polykrikoides</Emphasis>

The aim of this study was to isolate and identify algicidal bacteria against the dinoflagellate Cochlodinium polykrikoides, and to determine the algicidal activity and algicidal range. During the declining period of C. polykrikoides blooms, seven algicidal bacteria were isolated. The algicidal bacteria against C. polykrikoides were enumerated using the most probable number (MPN) method. The number of algicidal bacteria was high (3.7 × 10³ mL⁻¹). Algicidal bacteria were identified on the basis of biochemical and chemotaxonomic characteristics, and analysis of 16S rDNA sequences. Seven algicidal bacteria isolated in this study belonged to the genera Bacillus, Dietzia, Janibacter, and Micrococcus. The most algicidal bacterium, designated Micrococcus luteus SY-13, is assumed to produce secondary metabolites. When 5% culture filtrate of this strain was applied to C. polykrikoides cultures, over 90% of C. polykrikoides cells were destroyed within 6 h. M. luteus SY-13 showed significant algicidal activities against C. polykrikoides and a wide algicidal range against various harmful algal bloom (HAB) species. Taken together, our results suggest that M. luteus SY-13 could be a candidate for controlling HABs.