Electrochemical Sensing and Characterization of Aerobic Marine Bacterial Biofilms on Gold Electrode Surfaces

Reliable and accurate in situ sensors capable of detecting and quantifying troublesome marine biofilms on metallic surfaces are increasingly necessary. A 0.2 mm diameter gold electrochemical sensor was fully characterized using cyclic voltammetry in abiotic and biotic artificial seawater media within a continuous culture flow cell to detect the growth and development of an aerobic Pseudoalteromonas sp. biofilm. Deconvolution of the abiotic and biotic responses enable the constituent extracellular electron transfer and biofilm responses to be resolved. Differentiation of enhanced oxygen reduction kinetics within the aerobic bacterial biofilm is linked to enzyme and redox mediator activities.

Genetic examination of the marine bacterium Pseudoalteromonas luteoviolacea and effects of its metamorphosis-inducing factors

Pseudoalteromonas luteoviolacea is a globally distributed marine bacterium that stimulates the metamorphosis of marine animal larvae, an important bacteria-animal interaction that can promote the recruitment of animals to benthic ecosystems. Recently, different P. luteoviolacea isolates have been shown to produce two stimulatory factors that can induce tubeworm and coral metamorphosis; Metamorphosis-Associated Contractile structures (MACs) and tetrabromopyrrole (TBP) respectively. However, it remains unclear what proportion of P. luteoviolacea isolates possess the genes encoding MACs, and what phenotypic effect MACs and TBP have on other larval species. Here, we show that 9 of 19 sequenced P. luteoviolacea genomes genetically encode both MACs and TBP. While P. luteoviolacea biofilms producing MACs stimulate the metamorphosis of the tubeworm Hydroides elegans, TBP biosynthesis genes had no effect under the conditions tested. Although MACs are lethal to larvae of the cnidarian Hydractinia symbiologicarpus, P. luteoviolacea mutants unable to produce MACs are capable of stimulating metamorphosis. Our findings reveal a hidden complexity of interactions between a single bacterial species, the factors it produces and two species of larvae belonging to different phyla.

Characterization of Properties and Transglycosylation Abilities of Recombinant α-Galactosidase from Cold-Adapted Marine Bacterium Pseudoalteromonas KMM 701 and Its C494N and D451A Mutants

A novel wild-type recombinant cold-active α-d-galactosidase (α-PsGal) from the cold-adapted marine bacterium Pseudoalteromonas sp. KMM 701, and its mutants D451A and C494N, were studied in terms of their structural, physicochemical, and catalytic properties. Homology models of the three-dimensional α-PsGal structure, its active center, and complexes with D-galactose were constructed for identification of functionally important amino acid residues in the active site of the enzyme, using the crystal structure of the α-galactosidase from Lactobacillus acidophilus as a template. The circular dichroism spectra of the wild α-PsGal and mutant C494N were approximately identical. The C494N mutation decreased the efficiency of retaining the affinity of the enzyme to standard p-nitrophenyl-α-galactopiranoside (pNP-α-Gal). Thin-layer chromatography, matrix-assisted laser desorption/ionization mass spectrometry, and nuclear magnetic resonance spectroscopy methods were used to identify transglycosylation products in reaction mixtures. α-PsGal possessed a narrow acceptor specificity. Fructose, xylose, fucose, and glucose were inactive as acceptors in the transglycosylation reaction. α-PsGal synthesized -α(1→6)- and -α(1→4)-linked galactobiosides from melibiose as well as -α(1→6)- and -α(1→3)-linked p-nitrophenyl-digalactosides (Gal₂-pNP) from pNP-α-Gal. The D451A mutation in the active center completely inactivated the enzyme. However, the substitution of C494N discontinued the Gal-α(1→3)-Gal-pNP synthesis and increased the Gal-α(1→4)-Gal yield compared to Gal-α(1→6)-Gal-pNP.

Feeding and growth of the marine heterotrophic nanoflagellates, Procryptobia sorokini and Paraphysomonas imperforata on a bacterium, Pseudoalteromonas sp. with an inducible defence against grazing

Heterotrophic marine nanoflagellates are important grazers on bacteria in the water column. Some marine bacteria appear more resistant to grazing than do others. Marine nanoflagellates can be grown in the laboratory in batch cultures fed specific bacterial isolates. In some cultures, the flagellates appear unable to completely deplete the bacterial prey even when the bacterial strain otherwise is an excellent prey. This may indicate that some marine bacteria are able to induce defence mechanisms if they are grazed by nanoflagellates. Four morphologically distinct marine heterotrophic nanoflagellates, of which 3 were still identified as Procryptobia sorokini (Kinetoplastea) and one as Paraphysomonas imperforata (Chrysophyceae) were isolated from a coastal location along with 3 isolates of the marine bacterium Pseudoalteromonas sp. Flagellate growth and grazing on bacterial prey were analysed in batch cultures. Pseudoalteromonas was a suitable prey for all 4 flagellate isolates. They grazed and grew on Pseudoalteromonas as sole prey with maximal cell-specific growth rates of 0.1–0.25 h^-1 and gross growth efficiencies of 38–61%. Exposure to dense flagellate cultures or their supernatants did, however, cause a fraction of the Pseudoalteromonas cells to aggregate and the bacterium became apparently resistant to grazing. Concentrations of suspended Pseudoalteromonas cells were therefore not decreased below 1,700–7,500 cells μL^-1 by any of the flagellate isolates. These results indicate that Pseudoalteromonas sp. can be an excellent prey to marine nanoflagellates but also that is in possession of inducible mechanisms that protect against flagellate grazing.

Comparative expression analysis of immune-related factors in the sea cucumber Apostichopus japonicus

In order to preliminarily explore the joint involvement of different immune-related factors during the same immune process in Apostichopus japonicus, the transcriptional expression of Cu/Zn superoxide dismutase (Cu/Zn-SOD), catalase (CAT), c-type lysozyme (c-LYZ), i-type lysozyme (i-LYZ), cathepsin D, melanotransferrin (MTF), Toll, c-type lectin (c-LCT) and complement 3 (C3) during the development from fertilized eggs to juveniles and after challenging the juveniles with Vibrio splendidus, Pseudoalteromonas nigrifaciens, Shewanella baltica and Bacillus cereus, respectively, was measured using the method of quantitative real-time PCR (qRT-PCR), and then the correlations among different immune-related factors were analyzed. The results showed that the selected immune-related factors were expressed at all of the determined developmental stages and significantly up-regulated at doliolaria stage, suggesting the selected factors are indispensable immune components and the immune system might be broadly activated at doliolaria stage in A. japonicus. After challenged with four pathogenic bacteria, Cu/Zn-SOD, CAT, i-LYZ, cathepsin D, MTF, Toll, C3 were all significantly down-regulated at 4 h, indicating that some components of A. japonicus immune system might be inhibited at the beginning of pathogenic bacteria invasion. The immune-responsive analysis also showed that the significant regulation in Toll after challenged with four tested bacteria, that in MTF after challenged with S. baltica and that in C3 after challenged with P. nigrifaciens were all minus, suggesting Toll, MTF and C3 are probably the primary targets of pathogenic bacteria attack. Furthermore, the correlation analysis indicated that, all of the selected immune-related factors except cathepsin D might be in the same immune regulatory network during A. japonicus development, while all of the selected immune-related factors except c-LYZ might be in the same responsive regulatory network after challenged with four pathogenic bacteria. Altogether, A. japonicus immune system exhibited high complexity in regulation during organism development and after bacterial challenges.

Pseudoalteromonas piratica strain OCN003 is a coral pathogen that causes a switch from chronic to acute Montipora white syndrome in Montipora capitata

Reports of mass coral mortality from disease have increased over the last two decades. Montipora white syndrome (MWS) is a tissue loss disease that has negatively impacted populations of the coral Montipora capitata in Kāne'ohe Bay, Hawai'i. Two types of MWS have been documented; a progressive disease termed chronic MWS (cMWS), that can be caused by Vibrio owensii strain OCN002, and a comparatively faster disease termed acute MWS (aMWS), that can be caused by Vibrio coralliilyticus strain OCN008. M. capitata colonies exhibiting cMWS can spontaneously switch to aMWS in the field. In this study, a novel Pseudoalteromonas species, P. piratica strain OCN003, fulfilled Koch's postulates of disease causation as another etiological agent of aMWS. Additionally, OCN003 induced a switch from cMWS to aMWS on M. capitata in laboratory infection trials. A comparison of OCN003 and Vibrio coralliilyticus strain OCN008, showed that OCN003 was more effective at inducing the cMWS to aMWS switch in M. capitata than OCN008. This study is the first to demonstrate that similar disease signs on one coral species (aMWS on M. capitata) can be caused by multiple pathogens, and describes the first Pseudoalteromonas species that infects coral.

PfmA, a novel quorum-quenching N-acylhomoserine lactone acylase from Pseudoalteromonas flavipulchra

Many bacteria, such as Proteobacteria, Cyanobacteria and Bacteroidetes, use N-acylhomoserine lactones (AHLs) as quorum-sensing (QS) signal molecules for communication. Enzymatic degradation of AHLs, such as AHL acylase and AHL lactonase, can degrade AHLs (quorum quenching, QQ) to attenuate or disarm the virulence of pathogens. QQ is confirmed to be common in marine bacterial communities. Many genes encoding AHL acylases are found in marine bacteria and metagenomic collections, but only a few of these have been characterized in detail. We have reported that the marine bacterium Pseudoalteromonas flavipulchra JG1 can degrade AHLs. In the present study, a novel AHL acylase PfmA, which can degrade AHLs with acyl chains longer than 10 carbons, was identified from strain JG1. Ultra-performance liquid chromatography (UPLC) and electrospray ionization mass spectrometry (ESI-MS) analysis demonstrated that PfmA functions as an AHL acylase, which hydrolysed the amide bond of AHL. The purified PfmA of P. flavipulchra JG1 showed optimum activity at 30 °C and pH 7.0. PfmA belongs to the N-terminal nucleophile (Ntn) hydrolase superfamily and showed homology to a member of penicillin amidases, but PfmA can degrade ampicillin but not penicillin G. The residue Ser256 in PfmA is the active site according to site-directed mutagenesis. Furthermore, PfmA reduced AHL accumulation and the production of virulence factors in Vibrio anguillarum VIB72 and Pseudomonas aeruginosa PAO1, and attenuated the virulence of P. aeruginosa to increase Artemia survival, which suggested that PfmA can be considered as a therapeutic agent to control AHL-mediated pathogenicity.

Physiological and genomic features of a novel violacein-producing bacterium isolated from surface seawater

Strains JW1^T and JW3, isolated from surface seawater of the Arabian Sea, were subjected to polyphasic taxonomic analysis. Cells of both strains were Gram-stain-negative, aerobic, and rod-shaped. They formed violet pigment and produced violacein. On the basis of 16S rRNA gene sequence analysis, strains JW1^T and JW3 showed high 16S rRNA gene sequence similarity with Pseudoalteromonas byunsanensis JCM12483^T (98.2%), P. shioyasakiensis SE3^T (97.8%), P. arabiensis JCM 17292^T (97.3%), and P. gelatinilytica NH153^T (97.1%). The 16S rRNA gene sequence similarity between JW1^T and JW3 was 100%. Phylogenetic analyses revealed that both strains fell within the cluster of the genus Pseudoalteromonas and represented an independent lineage. The average nucleotide identity and in silico DNA-DNA hybridization values between JW1^T and type strains of the closely related Pseudoalteromonas species were 70.9–83.3% and 20.0–26.4%, respectively. The sole respiratory quinone in both strains is ubiquinone 8 (Q-8). The principal fatty acids are summed feature 3 (C_16:1ω7c and/or iso-C_15:0 2OH), C_18:1ω7c, and C_16:0. The major polar lipids are phosphatidylethanolamine, phosphatidylglycerol, one unidentified glycolipid, one unidentified aminolipid, and one unidentified phospholipid. The DNA G+C content was 43.3 mol%. Differential phylogenetic distinctiveness, chemotaxonomic differences, and phenotypic properties indicated that strains JW1^T and JW3 could be differentiated from the Pseudoalteromonas species with validly published names. Therefore, it is proposed that strains JW1^T and JW3 represent a novel species of the genus Pseudoalteromonas, for which the name Pseudoalteromonas amylolytica sp. nov. (type strain, JW1^T = CGMCC 1.15681^T = KCTC 52406^T = MCCC 1K02162^T) is proposed.

Screening of bromotyramine analogues as antifouling compounds against marine bacteria

Rapid and efficient synthesis of 23 analogues inspired by bromotyramine derivatives, marine natural products, by means of CuSO4-catalysed [3+2] alkyne-azide cycloaddition is described. The final target was then assayed for anti-biofilm activity against three Gram-negative marine bacteria, Pseudoalteromonas ulvae (TC14), Pseudoalteromonas lipolytica (TC8) and Paracoccus sp. (4M6). Most of the synthesised bromotyramine/triazole derivatives are more active than the parent natural products Moloka'iamine (A) and 3,5-dibromo-4-methoxy-β-phenethylamine (B) against biofilm formation by the three bacterial strains. Some of these compounds were shown to act as non-toxic inhibitors of biofilm development with EC50 < 200 μM without any effect on bacterial growth even at high concentrations (200 μM).

In Situ Confocal Raman Microscopy of Hydrated Early Stages of Bacterial Biofilm Formation on Various Surfaces in a Flow Cell

Bacterial biofilms are precursors to biofouling by other microorganisms. Understanding their initiation may allow us to design better ways to inhibit them, and thus to inhibit subsequent biofouling. In this study, the ability of confocal Raman microscopy to follow the initiation of biofouling by a marine bacterium, Pseudoalteromonas sp. NCIMB 2021 (NCIMB 2021), in a flow cell, using optical and confocal Raman microscopy, was investigated. The base of the flow cell comprised a cover glass. The cell was inoculated and the bacteria attached to, and grew on, the cover glass. Bright field images and Raman spectra were collected directly from the hydrated biofilms over several days. Although macroscopically the laser had no effect on the biofilm, within the first 24 h cells migrated away from the position of the laser beam. In the absence of flow, a buildup of extracellular substances occurred at the base of the biofilm. When different coatings were applied to cover glasses before they were assembled into the flow cells, the growth rate, structure, and composition of the resulting biofilm was affected. In particular, the ratio of Resonance Raman peaks from cytochrome c (CC) in the extracellular polymeric substances, to the Raman phenylalanine (Phe) peak from protein in the bacteria, depended on both the nature of the surface and the age of the biofilm. The ratios were highest for 24 h colonies on a hydrophobic surface. Absorption of a surfactant with an ethyleneoxy chain into the hydrophobic coating created a surface similar to that given with a simple PEG coating, where bacteria grew in colonies away from the surface rather than along the surface, and CC:Phe ratios were initially low but increased at least fivefold in the first 48 h.

Elevated nutrients change bacterial community composition and connectivity: high throughput sequencing of young marine biofilms

Biofilms are integral to many marine processes but their formation and function may be affected by anthropogenic inputs that alter environmental conditions, including fertilisers that increase nutrients. Density composition and connectivity of biofilms developed in situ (under ambient and elevated nutrients) were compared using 454-pyrosequencing of the 16S gene. Elevated nutrients shifted community composition from bacteria involved in higher processes (eg Pseudoalteromonas spp. invertebrate recruitment) towards more nutrient-tolerant bacterial species (eg Terendinibacter sp.). This may enable the persistence of biofilm communities by increasing resistance to nutrient inputs. A core biofilm microbiome was identified (predominantly Alteromonadales and Oceanospirillales) and revealed shifts in abundances of core microbes that could indicate enrichment by fertilisers. Fertiliser decreased density and connectivity within biofilms indicating that associations were disrupted perhaps via changes to energetic allocations within the core microbiome. Density composition and connectivity changes suggest nutrients can affect the stability and function of these important marine communities.

Polysiloxane-based block copolymers with marine bacterial anti-adhesion properties

Di- and triblock copolymers based on tert-butyldimethylsilyl methacrylate (MASi) and poly(dimethylsiloxane) (PDMS) macro-RAFT agents were synthesized resulting in copolymers with predictable molar masses and low dispersities (Đ < 1.2). The block copolymers exhibited two glass transition temperatures, corresponding to the PDMS- and poly(tert-butyldimethylsilyl methacrylate) (PMASi)-enriched phases, respectively. Contact angle measurements revealed the influence of the copolymer composition on their surface free energy, with block copolymers exhibiting surface free energies as low as 15.0 mJ m(-2). A laboratory assay using 96-well plates was used to assess the activity of the block copolymers against two marine bacteria (Pseudoalteromonas sp. and Shewanella sp.) isolated from the Mediterranean Sea. Coatings based on PDMS-based block copolymers demonstrated anti-adhesive performances against the two strains better than that of the coating containing only PMASi-based polymers. Coatings based on diblock copolymers demonstrated antifouling performances in the field that were better than those of the corresponding coatings containing triblock copolymers. Results of both lab and field assays showed that the antifouling properties were related to coatings possessing the highest receding water contact angle.

Antibiofilm Activity of the Marine Bacterium Pseudoalteromonas sp. 3J6 Against Vibrio tapetis, the Causative Agent of Brown Ring Disease

Vibrio tapetis CECT4600 is a pathogenic Gram-negative bacterium causing the brown ring disease in the Manila clam Ruditapes philippinarum. This vibriosis is induced by bacterial attachment on the periostracal lamina, yielding a decalcification of the bivalve shell. As in many bacterial species, pathogenesis is likely related to biofilm formation. The proteinaceous exoproducts of the marine bacterium Pseudoalteromonas sp. 3J6 inhibit the formation of biofilm by most of the tested marine bacteria without affecting their planktonic growth. In the present work, we examined the sensitivity of V. tapetis to Pseudoalteromonas sp. 3J6 and its exoproducts. In V. tapetis CECT4600-GFP-Pseudoalteromonas sp. 3J6 co-cultures, the latter outcompeted V. tapetis whatever the growth mode (planktonic or biofilm), which could result from a slower growth of V. tapetis. Biofilms containing only V. tapetis were grown in vitro on a glass substratum under dynamic conditions. When the glass was coated with a culture supernatant of Pseudoalteromonas sp. 3J6 (SN(3J6)) prior to inoculating V. tapetis CECT4600-GFP, the bacterial attachment was about fivefold lower than in control experiment without SN3J6 and the biofilm formation was delayed by about 24 h: A full biofilm was obtained at 48 versus 24 h for the control. Moreover, a preformed V. tapetis biofilm (grown on SN(3J6)-free glass substratum) could be disrupted by incubating it with SN3J6. This data suggest that Pseudoalteromonas sp. 3J6 is a good candidate to set up an anti-V. tapetis strategy usable in aquaculture to grow V. tapetis-free Manila clam spats.

A protective coat of microorganisms on macroalgae: inhibitory effects of bacterial biofilms and epibiotic microbial assemblages on barnacle attachment

Effects of epibiotic bacteria associated with macroalgae on barnacle larval attachment were investigated. Eight bacterial isolates obtained from samples of three macroalga species were cultured as monospecies bacterial films and tested for their activity against barnacle (Amphibalanus improvisus) attachment in field experiments (Western Baltic Sea). Furthermore, natural biofilm communities associated with the surface of the local brown alga, Fucus vesiculosus, which were exposed to different temperatures (5, 15 and 20 °C), were harvested and subsequently tested. Generally, monospecies bacterial biofilms, as well as natural microbial assemblages, inhibited barnacle attachment by 20-67%. denaturing gradient gel electrophoresis fingerprints showed that temperature treatment shifted the bacterial community composition and weakened the repellent effects at 20 °C. Repellent effects were absent when settlement pressure of cyprids was high. Nonviable bacteria tended to repel cyprids when compared to the unfilmed surfaces. We conclude that biofilms can have a repellent effect benefiting the host by preventing heavy fouling on its surface. However, severe settlement pressure, as well as stressful temperature, may reduce the protective effects of the alga's biofilm. Our results add to the notion that the performance of F. vesiculosus may be reduced by multiple stressors in the course of global warming.

Bacteriostatic anti-Vibrio parahaemolyticus activity of Pseudoalteromonas sp. strains DIT09, DIT44 and DIT46 isolated from Southern Chilean intertidal Perumytilus purpuratus

We characterised the anti-Vibrio parahaemolyticus (anti-V. parahaemolyticus) marine bacteria DIT09, DIT44 and DIT46 isolated from the intertidal mussel Perumytilus purpuratus. The 16S rRNA gene sequences identify a Pseudoalteromonas sp. that form a clade with P. prydzensis and P. mariniglutinosa. The strains produced bacteriostatic anti-V. parahaemolyticus agents during the exponential growth phase, which were also active against V. cholerae and V. anguillarum, but not on other Gram positive and Gram negative bacteria. Bacteriostatic agents could be permeated by analytic ultra-filtration with 3.5 kDa cut-off, partially precipitated with 70 and 90 % ammonium sulphate, but not extracted with ethyl acetate. Reverse-phase HPLC revealed the production of a set of 5-6 active compounds by each strain (elution from 20 to 40 % acetonitrile), with similar but non identical HPLC patterns. Additionally, V. parahaemolyticus was able to progressively overcome the inhibition of antibiotics in trypticase soy agar with Fe(III) 0.5 up to 2 mM, suggesting the involvement of a set of novel siderophore or active molecules targeted at different Fe-siderophore uptake systems. The overall findings suggest that Pseudoalteromonas sp. DIT strains produce a putatively novel class of bacteriostatic and probably amphiphilic anti-Vibrio agents, indicating the need for further studies with chemical purification followed by their structural and functional characterization. Finally, the crude cell-free extracts, as well as the strains incubated at 10(3) and 10(5) c.f.u./mL, did not cause mortality in Artemia franciscana nauplii, suggesting that these bacteria are serious candidates for further probiotic evaluations with shellfish and fish cultures.

Bacterial diversity in biofilms formed on condenser tube surfaces in a nuclear power plant

To elucidate the bacterial diversity in biofilms formed on a condenser tube from a nuclear power plant, 16S rRNA gene sequences were examined using a PCR-cloning-sequencing approach. Twelve operational taxonomic units were retrieved in the clone library, and the estimated species richness was low (13.2). Most of the clones (94.7%) were affiliated with α-Proteobacteria; Planctomycetes and γ-Proteobacteria were much rarer. Interestingly, except for one clone belonging to Pseudoalteromonas, most of the sequences displayed sequence similarities <97% of those of the closest type strains. Based on 16S rRNA phylogenetic analysis, most bacteria were assigned to novel taxa above the species level. The low species richness and unusual bacterial composition may be attributable to selective pressure from chlorine in the cooling water. To prevent or control bacterial biofilms in cooling circuits, additional studies of the physiology and ecology of these species will be essential.

Analysis of the Pseudoalteromonas tunicata genome reveals properties of a surface-associated life style in the marine environment

BACKGROUND

Colonisation of sessile eukaryotic host surfaces (e.g. invertebrates and seaweeds) by bacteria is common in the marine environment and is expected to create significant inter-species competition and other interactions. The bacterium Pseudoalteromonas tunicata is a successful competitor on marine surfaces owing primarily to its ability to produce a number of inhibitory molecules. As such P. tunicata has become a model organism for the studies into processes of surface colonisation and eukaryotic host-bacteria interactions.

METHODOLOGY/PRINCIPAL FINDINGS

To gain a broader understanding into the adaptation to a surface-associated life-style, we have sequenced and analysed the genome of P. tunicata and compared it to the genomes of closely related strains. We found that the P. tunicata genome contains several genes and gene clusters that are involved in the production of inhibitory compounds against surface competitors and secondary colonisers. Features of P. tunicata's oxidative stress response, iron scavenging and nutrient acquisition show that the organism is well adapted to high-density communities on surfaces. Variation of the P. tunicata genome is suggested by several landmarks of genetic rearrangements and mobile genetic elements (e.g. transposons, CRISPRs, phage). Surface attachment is likely to be mediated by curli, novel pili, a number of extracellular polymers and potentially other unexpected cell surface proteins. The P. tunicata genome also shows a utilisation pattern of extracellular polymers that would avoid a degradation of its recognised hosts, while potentially causing detrimental effects on other host types. In addition, the prevalence of recognised virulence genes suggests that P. tunicata has the potential for pathogenic interactions.

CONCLUSIONS/SIGNIFICANCE

The genome analysis has revealed several physiological features that would provide P. tunciata with competitive advantage against other members of the surface-associated community. We have also identified properties that could mediate interactions with surfaces other than its currently recognised hosts. This together with the detection of known virulence genes leads to the hypothesis that P. tunicata maintains a carefully regulated balance between beneficial and detrimental interactions with a range of host surfaces.

[Antibacterial activity of sponge associated marine bacterium Pseudoalteromonas sp. NJ6-3-1 regulated by quorum sensing]

OBJECTIVE

We chose a sponge-associated marine-bacterium Pseudoalteromonas piscicida NJ6-3-1 to study whether its antibacterial activity were regulated by quorum sensing.

METHODS

We studied the relationship between the antibacterial activity and bacterial density under various growth conditions. To simulate the natural competitive environment, we monitored the antibacterial activity at low cell density when the species were co-cultured with Staphylococcus aureus.

RESULTS

Antibacterial activity correlated closely with cell density. Marine bacterium NJ6-3-1 started producing antibacterial compounds when cell density reached the threshold value of OD(630) = 0.4. Some signal molecules existing in the metabolites of S. aureus could induce the production of antibacterial substance by marine-bacteria NJ6-3-1 even cell density below the required threshold.

CONCLUSION

The results provide preliminary evidence to support the hypothesis that the antibacterial activity of NJ6-3-1 was regulated by the quorum sensing system of intraspecies and interspecies.

A novel lysis system in PM2, a lipid-containing marine double-stranded DNA bacteriophage

In this study we investigated the lysis system of the lipid-containing double-stranded DNA bacteriophage PM2 infecting Gram-negative marine Pseudoalteromonas species. We analysed wt and lysis-deficient phage-induced changes in the host physiology and ascribed functions to two PM2 gene products (gp) involved in lysis. We show that bacteriophage PM2 uses a novel system to disrupt the infected cell. The novelty is based on the following findings: (i) gp k is needed for the permeabilization of the cytoplasmic membrane and appears to play the role of a typical holin. However, its unique primary structure [53 aa, 1 transmembrane domain (TMD)] places it into a new class of holins. (ii) We have proposed that, unlike other bacteriophages studied, PM2 relies on lytic factors of the cellular origin for digestion of the peptidoglycan. (iii) gp l (51 aa, no TMDs) is needed for disruption of the outer membrane, which is highly rigidified by the divalent cations abundant in the marine environment. The gp l has no precedent in other phage lytic systems studied so far. However, the presence of open reading frame l-like genes in genomes of other bacterial viruses suggests that the same system might be used by other phages and is not unique to PM2.

Effect of biofilm formation by Pseudoalteromonas spongiae on induction of larval settlement of the polychaete Hydroides elegans

The effects of culture conditions and chloramphenicol treatment on the induction of the marine bacterium Pseudoalteromonas spongiae to larval settlement of Hydroides elegans were investigated. The results showed that P. spongiae cells grown in the medium containing both yeast extract and peptone (YP-grown P. spongiae) was highly inductive to larval settlement, whereas P. spongiae cells grown in the medium containing only peptone (P-grown P. spongiae) or YP-grown P. spongiae cells treated with chloramphenicol at the onset of biofilm development (YPC-grown P. spongiae) did not induce larval settlement. Analysis of biofilm formation, biofilm structure, and the surface protein profile indicated that only the induction-capable YP-grown P. spongiae formed a well-developed biofilm, while the P-grown P. spongiae and the YPC-grown P. spongiae did not. We report here for the first time that bacterial biofilm formation was associated with its induction of larval settlement.

A marine bacterial adhesion microplate test using the DAPI fluorescent dye: a new method to screen antifouling agents

AIMS

To develop a method to screen antifouling agents against marine bacterial adhesion as a sensitive, rapid and quantitative microplate fluorescent test.

METHODS AND RESULTS

Our experimental method is based on a natural biofilm formed by mono-incubation of the marine bacterium Pseudoalteromonas sp. D41 in sterile natural sea water in a 96-well polystyrene microplate. The 4'6-diamidino-2-phenylindole dye was used to quantify adhered bacteria in each well. The total measured fluorescence in the wells was correlated with the amount of bacteria showing a detection limit of one bacterium per 5 microm(2) and quantifying 2 x 10(7) to 2 x 10(8) bacteria adhered per cm(2). The antifouling properties of three commercial surface-active agents and chlorine were tested by this method in the prevention of adhesion and also in the detachment of already adhered bacteria. The marine bacterial adhesion inhibition rate depending on the agent concentration showed a sigmoid shaped dose-response curve.

CONCLUSIONS

This test is well adapted for a rapid and quantitative first screening of antifouling agents directly in seawater in the early steps of marine biofilm formation.

SIGNIFICANCE AND IMPACT OF THE STUDY

In contrast to the usual screenings of antifouling products which detect a bactericidal activity, this test is more appropriate to screen antifouling agents for bacterial adhesion removal or bacterial adhesion inhibition activities. This screening test focuses on the antifouling properties of the products, especially the initial steps of marine biofilm formation.

Intrinsic halotolerance of the psychrophilic alpha-amylase from Pseudoalteromonas haloplanktis

The halotolerance of a cold adapted alpha-amylase from the psychrophilic bacterium Pseudoalteromonas haloplanktis (AHA) was investigated. AHA exhibited hydrolytic activity over a broad range of NaCl concentrations (0.01-4.5 M). AHA showed 28% increased activity in 0.5-2.0 M NaCl compared to that in 0.01 M NaCl. In contrast, the corresponding mesophilic (Bacillus amyloliquefaciens) and thermostable (B. licheniformis) alpha-amylases showed a 39 and 46% decrease in activity respectively. Even at 4.5 M NaCl, 80% of the initial activity was detected for AHA, whereas the mesophilic and thermostable enzymes were inactive. Besides an unaltered fluorescence emission and secondary structure, a 10 degrees C positive shift in the temperature optimum, a stabilization factor of >5 for thermal inactivation and a Delta T(m) of 8.3 degrees C for the secondary structure melting were estimated in 2.7 M NaCl. The higher activation energy, half-life time and T(m) indicated reduced conformational dynamics and increased rigidity in the presence of higher NaCl concentrations. A comparison with the sequences of other halophilic alpha-amylases revealed that AHA also contains higher proportion of small hydrophobic residues and acidic residues resulting in a higher negative surface potential. Thus, with some compromise in cold activity, psychrophilic adaptation has also manifested halotolerance to AHA that is comparable to the halophilic enzymes.

Chromosomal context directs high-frequency precise excision of IS492 in Pseudoalteromonas atlantica

DNA rearrangements, including insertions, deletions, and inversions, control gene expression in numerous prokaryotic and eukaryotic systems, ranging from phase variation of surface antigens in pathogenic bacteria to generation of Ig diversity in human B cells. We report here that precise excision of the mobile element IS492 from one site on the Pseudoalteromonas atlantica chromosome directly correlates with phase variation of peripheral extracellular polysaccharide ((p)EPS) production from OFF (epsG::IS492) to ON (epsG(+)). In a previously undescribed application of quantitative PCR, we determined that the frequency of this transposase-dependent precise excision is remarkably high, ranging from 10(-3) to 10(-2) per cell per generation. High-frequency excision resulting in nonmutagenic repair of donor DNA is extremely unusual for classical transposable elements. Interestingly, high-frequency precise excision of IS492 does not occur at four different insertion sites on the P. atlantica chromosome, despite identity in the IS492 nucleotide sequences and 5- to 7-bp flanking DNA. The genome sequence revealed that epsG-associated IS492 is the only element inserted within a gene. Quantitative RT-PCR assays for externally derived transposase transcripts from each IS492 copy showed that IS492 at epsG has higher levels of host-initiated transcription through the element, suggesting that transcription per se or an increase in transposase (mooV) expression is responsible for the effect of chromosomal position on element excision. MooV levels and excision activity for IS492 inserted in forward and reverse orientations relative to plac and pT7 in Escherichia coli support that external transcription of mooV boosts transposase to a critical level required for detectable excision.

Inhibition of fouling by marine bacteria immobilised in kappa-carrageenan beads

Antifouling solutions that leave little or no impact in the world's oceans are constantly being sought. This study employed the immobilisation of the antifouling bacterium Pseudoalteromonas tunicata in kappa-carrageenan to demonstrate how a surface may be protected from fouling by bacteria, i.e. a 'living paint'. Attempts so far to produce a 'living paint' have been limited in both longevity of effectiveness and demonstration of applicability, most noticeably regarding the lack of any field data. Here survival of bacteria immobilised in kappa-carrageenan for 12 months in the laboratory is demonstrated and evidence presented for inhibition of fouling for up to 7 weeks in the field (Sydney Harbour, NSW, Australia).

Inhibition of fungal colonization by Pseudoalteromonas tunicata provides a competitive advantage during surface colonization

The marine epiphytic bacterium Pseudoalteromonas tunicata produces a range of extracellular secondary metabolites that inhibit an array of common fouling organisms, including fungi. In this study, we test the hypothesis that the ability to inhibit fungi provides P. tunicata with an advantage during colonization of a surface. Studies on a transposon-generated antifungal-deficient mutant of P. tunicata, FM3, indicated that a long-chain fatty acid-coenzyme A ligase is involved in the production of a broad-range antifungal compound by P. tunicata. Flow cell experiments demonstrated that production of an antifungal compound provided P. tunicata with a competitive advantage against a marine yeast isolate during surface colonization. This compound enabled P. tunicata to disrupt an already established fungal biofilm by decreasing the number of yeast cells attached to the surface by 66% +/- 9%. For in vivo experiments, the wild-type and FM3 strains of P. tunicata were used to inoculate the surface of the green alga Ulva australis. Double-gradient denaturing gradient gel electrophoresis analysis revealed that after 48 h, the wild-type P. tunicata had outcompeted the surface-associated fungal community, whereas the antifungal-deficient mutant had no effect on the fungal community. Our data suggest that P. tunicata is an effective competitor against fungal surface communities in the marine environment.

Metalloid reducing bacteria isolated from deep ocean hydrothermal vents of the Juan de Fuca Ridge, Pseudoalteromonas telluritireducens sp. nov. and Pseudoalteromonas spiralis sp. nov

Five strains of Gram-negative, rod, curved rod and spiral-shaped bacteria were isolated from the vicinity of deep ocean hydrothermal vents along the Main Endeavour Segment of the Juan de Fuca Ridge in the Pacific Ocean. All strains showed remarkable resistance to high levels of toxic metalloid oxyanions, and were capable of reducing the oxyanions tellurite and selenite to their less toxic elemental forms. Phylogenetic analysis of four strains identified these isolates as close relatives of the genus Pseudoalteromonas within the class Gammaproteobacteria. Pseudoalteromonas agarivorans was the closest relative of strains Te-1-1 and Se-1-2-redT, with, respectively, 99.5 and 99.8% 16S rDNA sequence similarity. Strain Te-2-2T was most closely related to Pseudoalteromonas paragorgicola, with 99.8% 16S rDNA sequence similarity. The DNA G+C base composition was 39.6 to 41.8 mol%, in agreement with other members of the genus Pseudoalteromonas. However, the isolates showed important morphological and physiological differences from previously described species of this genus, with one group forming rod-shaped bacteria typical of Pseudoalteromonas and the other forming vibrioid- to spiral-shaped cells. Based on these differences, and on phylogenetic data, we propose the creation of the new species Pseudoalteromonas telluritireducens sp. nov., with strain Se-1-2-redT (DSMZ = 16098T = VKM B-2382T) as the type strain, and Pseudoalteromonas spiralis sp. nov., with strain Te-2-2T (DSMZ = 16099T = VKM B-2383T) as the type strain.

Ecological advantages of autolysis during the development and dispersal of Pseudoalteromonas tunicata biofilms

In the ubiquitous marine bacterium Pseudoalteromonas tunicata, subpopulations of cells are killed by the production of an autocidal protein, AlpP, during biofilm development. Our data demonstrate an involvement of this process in two parameters, dispersal and phenotypic diversification, which are of importance for the ecology of this organism and for its survival within the environment. Cell death in P. tunicata wild-type biofilms led to a major reproducible dispersal event after 192 h of biofilm development. The dispersal was not observed with a DeltaAlpP mutant strain. Using flow cytometry and the fluorescent dye DiBAC4(3), we also show that P. tunicata wild-type cells that disperse from biofilms have enhanced metabolic activity compared to those cells that disperse from DeltaAlpP mutant biofilms, possibly due to nutrients released from dead cells. Furthermore, we report that there was considerable phenotypic variation among cells dispersing from wild-type biofilms but not from the DeltaAlpP mutant. Wild-type cells that dispersed from biofilms showed significantly increased variations in growth, motility, and biofilm formation, which may be important for successful colonization of new surfaces. These findings suggest for the first time that the autocidal events mediated by an antibacterial protein can confer ecological advantages to the species by generating a metabolically active and phenotypically diverse subpopulation of dispersal cells.

A mannose-sensitive haemagglutinin (MSHA)-like pilus promotes attachment of Pseudoalteromonas tunicata cells to the surface of the green alga Ulva australis

This study demonstrates that attachment of the marine bacterium Pseudoalteromonas tunicata to the cellulose-containing surface of the green alga Ulva australis is mediated by a mannose-sensitive haemagglutinin (MSHA-like) pilus. We have identified an MSHA pilus biogenesis gene locus in P. tunicata, termed mshI1I2JKLMNEGFBACDOPQ, which shows significant homology, with respect to its genetic characteristics and organization, to the MSHA pilus biogenesis gene locus of Vibrio cholerae. Electron microscopy studies revealed that P. tunicata wild-type cells express flexible pili peritrichously arranged on the cell surface. A P. tunicata mutant (SM5) with a transposon insertion in the mshJ region displayed a non-piliated phenotype. Using SM5, it has been demonstrated that the MSHA pilus promotes attachment of P. tunicata wild-type cells in polystyrene microtitre plates, as well as to microcrystalline cellulose and to the living surface of U. australis. P. tunicata also demonstrated increased pilus production in response to cellulose and its monomer constituent cellobiose. The MSHA pilus thus functions as a determinant of attachment in P. tunicata, and it is proposed that an understanding of surface sensing mechanisms displayed by P. tunicata will provide insight into specific ecological interactions that occur between this bacterium and higher marine organisms.

Unravelling the role of the ToxR-like transcriptional regulator WmpR in the marine antifouling bacterium Pseudoalteromonas tunicata

The dark-green-pigmented marine bacterium Pseudoalteromonas tunicata produces several target-specific compounds that act against a range of common fouling organisms, including bacteria, fungi, protozoa, invertebrate larvae and algal spores. The ToxR-like regulator WmpR has previously been shown to regulate expression of bioactive compounds, type IV pili and biofilm formation phenotypes which all appear at the onset of stationary phase. In this study a comparison of survival under starvation or stress between the wild-type P. tunicata strain and a wmpR mutant (D2W2) does not suggest a role for WmpR in regulating starvation- and stress-resistant phenotypes such as those that may be required in stationary phase. Both proteomic [2-dimensional PAGE (2D-PAGE)] and transcriptomic (RNA arbitrarily primed PCR) studies were used to discover members of the WmpR regulon. 2D-PAGE identified 11 proteins that were differentially expressed by WmpR. Peptide sequence data were obtained for six of these proteins and identified using the draft P. tunicata genome as being involved in protein synthesis, amino acid transamination and ubiquinone biosynthesis, as well as hypothetical proteins. The transcriptomic analysis identified three genes significantly up-regulated by WmpR, including a TonB-dependent outer-membrane protein, a non-ribosomal peptide synthetase and a hypothetical protein. Under iron-limitation the wild-type showed greater survival than D2W2, indicating the importance of WmpR under these conditions. Results from these studies show that WmpR controls the expression of genes encoding proteins involved in iron acquisition and uptake, amino acid metabolism and ubiquinone biosynthesis in addition to a number of proteins with as yet unknown functions.

Coping with cold: the genome of the versatile marine Antarctica bacterium Pseudoalteromonas haloplanktis TAC125

A considerable fraction of life develops in the sea at temperatures lower than 15 degrees C. Little is known about the adaptive features selected under those conditions. We present the analysis of the genome sequence of the fast growing Antarctica bacterium Pseudoalteromonas haloplanktis TAC125. We find that it copes with the increased solubility of oxygen at low temperature by multiplying dioxygen scavenging while deleting whole pathways producing reactive oxygen species. Dioxygen-consuming lipid desaturases achieve both protection against oxygen and synthesis of lipids making the membrane fluid. A remarkable strategy for avoidance of reactive oxygen species generation is developed by P. haloplanktis, with elimination of the ubiquitous molybdopterin-dependent metabolism. The P. haloplanktis proteome reveals a concerted amino acid usage bias specific to psychrophiles, consistently appearing apt to accommodate asparagine, a residue prone to make proteins age. Adding to its originality, P. haloplanktis further differs from its marine counterparts with recruitment of a plasmid origin of replication for its second chromosome.

Calcium influences cellular and extracellular product formation during biofilm-associated growth of a marine Pseudoalteromonas sp

Bacteria undergo a variety of physiological changes following a switch from planktonic growth to surface-associated biofilm growth. Here, it is shown that biofilm development of a marine isolate, Pseudoalteromonas sp. 1398, results in global changes in its cytosolic and extracellular proteomes. Calcium influences these proteome responses, and affects the amount of surface-associated biomass and extracellular matrix material produced by Pseudoalteromonas sp. 1398. Four extracellular proteins, characterized by N-terminal sequencing, showed increased abundances, while one protein, flagellin, showed reduced abundance at higher [Ca2+]. Immunoblotting and transmission-electron-microscopy analysis confirmed that higher [Ca2+] and surface-associated growth results in the repression of flagella production. Two-dimensional gel electrophoresis (2DGE) studies combined with cluster analysis of global proteome responses demonstrated that Ca2+ had a greater regulatory influence on Pseudoalteromonas sp. growing in biofilms than on planktonic cultures. Approximately 22 % of the total cytosolic proteins resolved by 2DGE had differing abundances in response to a switch from planktonic growth to surface-associated growth when the cells were cultivated in 1 mM Ca2+. At higher [Ca2+] this number increased to 38 %. Fifteen cellular proteins that were differentially expressed in response to biofilm growth and/or Ca2+ were analysed by N-terminal sequencing and/or MS/MS. These proteins were identified as factors involved in cellular metabolic functions, putative proteases and transport proteins, although there were several proteins that had not been previously characterized. These results indicate that Ca2+ causes global changes in matrix material, as well as in cellular and extracellular protein profiles of Pseudoalteromonas sp. 1398. These changes are more pronounced when the bacterium grows in biofilms than when it grows in planktonic culture.

Characterization of Pseudoalteromonas distincta-like sea-water isolates and description of Pseudoalteromonas aliena sp. nov

Seven melanogenic Pseudoalteromonas distincta-like strains, KMM 3562T, KMM 3536, KMM 3537, KMM 3538, KMM 3539, KMM 3615 and KMM 3629, which expressed tyrosinases were isolated from sea-water samples collected from different locations in Amursky Bay (Sea of Japan, Pacific Ocean) and characterized to clarify their taxonomic position. By 16S rRNA gene sequence analysis, the bacteria were shown to belong to the genus Pseudoalteromonas. The G + C content of the DNAs of the strains was 41-43 mol%. The level of DNA similarity among these strains was conspecific (92-97 %), indicating that they represented a single genospecies. However, DNA from the strains isolated from sea water showed only 63-65 % genetic relatedness with the DNA of the type strain P. distincta. The novel organisms grew mainly between 4 and 30 degrees C, were neutrophilic and slightly halophilic (four strains had a narrow range of growth between 3 and 6 % NaCl, w/v), were haemolytic and cytotoxic and were able to degrade starch, gelatin and Tween 80. The predominant fatty acids, including 16 : 0, 16 : 1omega7, 17 : 1omega7 and 18 : 1omega7, were typical of the genus Pseudolateromonas. The phylogenetic, genetic and physiological properties of the seven strains placed them within a novel species, Pseudoalteromonas aliena sp. nov., the type strain of which is SW19T (= KMM 3562T = LMG 22059T).

Selection and identification of autochthonous potential probiotic bacteria from turbot larvae (Scophthalmus maximus) rearing units

The purpose of this study was to select, identify and characterise bacteria as a disease control measure in the rearing of marine fish larvae (turbot, Scophthalmus maximus). Thirty-four out of 400 marine bacterial strains exhibited in vitro anti-bacterial activity against three fish larval pathogens. Two strains originated from culture collections and thirty two strains were isolated directly from turbot larvae rearing units using a pre-selection procedure to facilitate detection of antagonists. Approximately 8,500 colonies from colony-count plates were replica-plated on agar seeded with Vibrio anguillarum, and 196 of them caused zones of clearing in the V. anguillarum agar layer. Of these, 32 strains exhibited reproducible antibacterial properties in vitro when tested against the fish pathogens V. anguillarum 90-11-287, V. splendidus DMC-1 and a Pseudoalteromonas HQ. Seventeen antagonists were identified as Vibrio spp. and four of twelve tested were lethal to yolk-sac larvae. The 15 remaining strains were identified as Roseobacter spp. based on phenotypic criteria and 16S rDNA gene sequence analysis of two strains representing the two major RAPD groups. Most of the remaining 164 strains selected in the initial replica plating were identified as Vibrionaceae or Pseudoalteromonas. Roseobacter spp. were not lethal to egg yolk sac turbot larvae and in two of three trials, the mortality of larvae decreased (p > 0.001) in treatments where 10(7) cfu/ml Roseobacter sp. strain 27-4 was added, indicating a probiotic potential.

Purification and partial identification of novel antimicrobial protein from marine bacterium Pseudoalteromonas species strain X153

A marine bacterium, X153, was isolated from a pebble collected at St. Anne du Portzic (France). By 16S ribosomal DNA gene sequence analysis, X153 strain was identified as a Pseudoalteromonas sp. close to P. piscicida. The crude culture of X153 was highly active against human pathogenic strains involved in dermatologic diseases, and marine bacteria including various ichthyopathogenic Vibrio strains. The active substance occurred both in bacterial cells and in culture supernatant. An antimicrobial protein was purified to homogeneity by a 4-step procedure using size-exclusion and ion-exchange chromatography. The highly purified P-153 protein is anionic, and sodium dodecylsulfate polyacrylamide gel electrophoresis gives an apparent molecular mass of 87 kDa. The X153 bacterium protected bivalve larvae against mortality, following experimental challenges with ichthyopathogenic Vibrio. Pseudoalteromonas sp. X153 may be useful in aquaculture as a probiotic bacterium.

Impact of cultivation conditions on haemolytic activity of Pseudoalteromonas issachenkonii KMM 3549T

AIMS

The present work aimed to study the effects of cultivation conditions on the haemolytic activities of Pseudoalteromonas issachenkonii.

METHODS AND RESULTS

The kinetics of growth and haemolytic activities was investigated on sea-salts and NaCl-based nutrient media supplemented with either starch, or KBr over a period of 140 h. The first haemolytic activity occurred when bacterial cells reached the late stationary phase. The second haemolytic activity was observed in marine broth (MB) after 110 h of incubation. Addition of Fe to the culture medium neither affected bacterial growth nor reduced the haemolytic activity. However, the activity was enhanced in the presence of iron chelator. The second haemolytic activity was not affected by Ca2+, or inhibited by chymotrypsin or EDTA.

CONCLUSIONS

The production of haemolysins by P. issachenkonii was greater on MB and was dependent on both the medium composition and time of incubation. The second haemolytic activity was heat stable, nonproteinaceous, calcium-independent and was regulated by Fe.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results demonstrated the importance of optimization of both the media composition and monitoring the haemolytic activity over a prolonged cultivation time to detect different types of haemolysins.

Laser impact assessment in a biofilm-forming bacterium Pseudoalteromonas carrageenovora using a flow cytometric system

Impact by pulsed laser irradiations from an Nd:YAG laser on the marine biofilm-forming bacterium Pseudoalteromonas carrageenovora has been studied using a flow cytometric system. The biofilm-forming bacteria in the planktonic state have been irradiated while flowing, and the mortality and bacterial attachment have been determined by exposing TiN coupons in the system. Coupons suspended in the non-irradiated bacterial flow were treated as the control. The fluence used in the study was 0.1 J/cm(2). Three flow rates (14, 28, and 42 cm/min) and two exposure durations (15 and 30 min) were tested. The results showed the increase in bacterial mortality with the decrease in flow rate. The maximum mortality of 27.5% was observed when the flow rate was 14 cm/min. The bacterial attachment increased with the increase in flow rate and exposure duration. The area of bacterial attachment on the experimental coupons exposed to the irradiated sample was significantly lesser than that for the nonirradiated sample. The results thus show in a flowing system, low power pulsed laser irradiations could reduce the bacterial attachment even though it did not cause significant mortality.

MC21-A, a bactericidal antibiotic produced by a new marine bacterium, Pseudoalteromonas phenolica sp. nov. O-BC30(T), against methicillin-resistant Staphylococcus aureus

We previously reported a new marine bacterium, Pseudoalteromonas phenolica sp. nov. O-BC30(T), which produced a bactericidal antibiotic against methicillin-resistant Staphylococcus aureus (MRSA). In the present study, we purified an anti-MRSA substance (MC21-A) from the methanol extract of the cells of P. phenolica O-BC30(T) and analyzed its chemical structure. MC21-A was determined to be 3,3',5,5'-tetrabromo-2,2'-biphenyldiol by spectrometric analyses. Its anti-MRSA activity against 10 clinical isolates of MRSA was comparable to that of vancomycin (MC21-A MICs, 1 to 2 micro g/ml; vancomycin MICs, <0.25 to 2 micro g/ml). This substance was also high active against Enterococcus serolicida, Enterococcus faecium, and Enterococcus faecalis but was less active against Streptococcus spp. A time-kill study also demonstrated that MC21-A was bactericidal and that its killing rate was much higher than that of vancomycin. The postantibiotic effect (PAE) of MC21-A against a clinical MRSA isolate, strain E 31243, was also comparable to that of vancomycin (MC21-A PAEs, 1.46 to 1.65 h; vancomycin PAEs, 0.84 to 1.43 h). However, a lysis experiment demonstrated that this substance failed to lyse MRSA cells. This substance also did not lyse human erythrocytes. A SYTOX Green staining experiment implied that this substance permeabilized the cell membrane of MRSA as its mode of action. When its activities against a hypersensitive Escherichia coli mutant (KO 1489) and wild-type strains were tested, MC21-A exhibited higher levels of activity against the former. Furthermore, MC21-A was not cytotoxic to human normal fibroblast, rat pheochromocytoma, and Vero cells at concentrations up to 50 micro g/ml. These results suggest that MC21-A might be useful as a lead compound in the development of new types of anti-MRSA substances with modes of action different from those of vancomycin and teicoplanin.

Inhibition of bacterial attachment by pulsed Nd:YAG laser irradiations: an in vitro study using marine biofilm-forming bacterium Pseudoalteromonas carrageenovora

The effect of low mean power laser irradiations with short pulse duration from an Nd:YAG (neodymium-doped yttrium aluminium garnet) laser on a marine biofilm-forming bacterium, Pseudoalteromonas carrageenovora, was investigated in the laboratory. Laser-irradiated bacteria were tested for their ability to attach on nontoxic titanium nitride (TiN) coupons with nonirradiated bacteria as the reference. Two durations of irradiation were tested, 10 and 15 min. Bacterial attachment was monitored after 20 min, 40 min, and 1 h of irradiation. The average laser fluence used for this study was 0.1 J/cm(2). The area of attachment of the irradiated bacteria was significantly less than the reference for both durations of irradiation. The growth of irradiated bacteria showed a longer lag phase than the nonirradiated sample, mainly due to mortality in the former. The bacterial mortality observed was 23.4 +/- 0.71 and 48.6 +/- 6.5% for 10- and 15-min irradiations, respectively. Thus, the results show that low-power pulsed laser irradiations resulted in a significant bacterial mortality and a reduced bacterial attachment on nontoxic hard surfaces.

Impact of pulsed Nd:YAG laser on the marine biofilm-forming bacteria Pseudoalteromonas carrageenovora: significance of physiological status

The impact of pulsed Nd:YAG (neodymium-doped yttrium/aluminium garnet) laser irradiation on the marine biofilm-forming bacteria Pseudoalteromonas carrageenovora during two growth stages (log phase and stationary phase) and under two stresses (reduced temperature and nutrient limitation) was investigated. Bacteria were exposed to a laser fluence of 0.1 J x cm(-2) for 5, 10, and 15 min with a peak power of 20 MW x cm(-2), a pulse width of 5 ns, and an average power of 1 W x cm(-2) with a repetition rate of 10 Hz. The mortality of bacteria immediately after the irradiation as well as after a set period of time was determined. Mortality was higher among log-phase bacteria (72%) than bacteria in the stationary phase (51%) and those grown under nutrient limitation (51%). Bacteria grown at reduced temperature had a mortality of 49%. However, the differences in cell density of log-phase, stationary-phase, nutrient-limited, and low-temperature irradiated samples compared with controls after 5 h of incubation were 96, 93, 94, and 86%, respectively. The mortality values suggest that the same laser fluence has different degrees of effectiveness, depending on the physiological state of the bacteria.