Variation in biofilm formation among symbiotic and free-living strains of Vibrio fischeri

Toxicity monitoring of solvents, hydrocarbons, and heavy metals using statistically optimized model of luminous Vibrio sp. 6HFE

Background

The utilization of bioluminescent bacteria in environmental monitoring of water contaminates considers being a vital and powerful approach. This study aimed to isolate, optimize, and apply luminescent bacteria for toxicity monitoring of various toxicants in wastewater.

Results

On the basis of light intensity, strain Vibrio sp. 6HFE was initially selected, physiologically/morphologically characterized, and identified using the 16SrDNA gene. The luminescence production was further optimized by employing statistical approaches (Plackett-Burman design and central composite design). The maximum bioluminescence intensity recorded 1.53 × 10⁶ CPS using optimized medium containing (g/L), yeast extract (0.2g), CaCl₂ (4.0), MgSO₄ (0.1), and K₂HPO₄ (0.1) by 2.3-fold increase within 1h. The harnessing of Vibrio sp. 6HFE as a bioluminescent reporter for toxicity of organic solvents was examined using a bioluminescence inhibition assay. According to IC₅₀ results, the toxicity order of such pollutants was chloroform > isoamyl > acetic acid > formamide > ethyl acetate > acetonitrile > DMSO > acetone > methanol. However, among eight heavy metals tested, the bioluminescence was most sensitive to Ag⁺ and Hg⁺ and least sensitive to Co²⁺ and Ni²⁺. Additionally, the bioluminescence was inhibited by benzene, catechol, phenol, and penta-chlorophenol at 443.1, 500, 535.1, and 537.4 ppm.

Conclusion

Vibrio sp. 6HFE succeeded in pollution detection at four different environmental and wastewater samples revealing its efficiency in ecotoxicity monitoring.

Non-serogroup O1/O139 agglutinable Vibrio cholerae: a phylogenetically and genealogically neglected yet emerging potential pathogen of clinical relevance

Somatic antigen agglutinable type-1/139 Vibrio cholerae (SAAT-1/139-Vc) members or O1/O139 V. cholerae have been described by various investigators as pathogenic due to their increasing virulence potential and production of choleragen. Reported cholera outbreak cases around the world have been associated with these choleragenic V. cholerae with high case fatality affecting various human and animals. These virulent Vibrio members have shown genealogical and phylogenetic relationship with the avirulent somatic antigen non-agglutinable strains of 1/139 V. cholerae (SANAS-1/139- Vc) or O1/O139 non-agglutinating V. cholerae (O1/O139-NAG-Vc). Reports on implication of O1/O139-NAGVc members in most sporadic cholera/cholera-like cases of diarrhea, production of cholera toxin and transmission via consumption and/or contact with contaminated water/seafood are currently on the rise. Some reported sporadic cases of cholera outbreaks and observed change in nature has also been tracable to these non-agglutinable Vibrio members (O1/O139-NAGVc) yet there is a sustained paucity of research interest on the non-agglutinable V. cholerae members. The emergence of fulminating extraintestinal and systemic vibriosis is another aspect of SANAS-1/139- Vc implication which has received low attention in terms of research driven interest. This review addresses the need to appraise and continually expand research based studies on the somatic antigen non-serogroup agglutinable type-1/139 V. cholerae members which are currently prevalent in studies of water bodies, fruits/vegetables, foods and terrestrial environment. Our opinion is amassed from interest in integrated surveillance studies, management/control of cholera outbreaks as well as diarrhea and other disease-related cases both in the rural, suburban and urban metropolis.

Environmental Stress Selects for Innovations That Drive Vibrio Symbiont Diversity

Symbiotic bacteria in the Vibrionaceae are a dynamic group of γ-Proteobacteria that are commonly found throughout the world. Although they primarily are free-living in the environment, they can be commonly found associated with various Eukarya, either as beneficial or pathogenic symbionts. Interestingly, this dual lifestyle (free-living or in symbiosis) enables the bacteria to have enormous ecological breadth, where they can accommodate a variety of stresses in both stages. Here, we discuss some of the most common stressors that Vibrio bacteria encounter when in their free-living state or associated with an animal host, and how some of the mechanisms that are used to cope with these stressors can be used as an evolutionary advantage that increases their diversity both in the environment and within their specific hosts.

Identification of a Transcriptomic Network Underlying the Wrinkly and Smooth Phenotypes of Vibrio fischeri

Vibrio fischeri is a cosmopolitan marine bacterium that oftentimes displays different colony morphologies, switching from a smooth to a wrinkly phenotype in order to adapt to changes in the environment. This wrinkly phenotype has also been associated with increased biofilm formation, an essential characteristic for V. fischeri to adhere to substrates, to suspended debris, and within the light organs of sepiolid squids. Elevated levels of biofilm formation are correlated with increased microbial survival of exposure to environmental stressors and the ability to expand niche breadth. Since V. fischeri has a biphasic life history strategy between its free-living and symbiotic states, we were interested in whether the wrinkly morphotype demonstrated differences in its expression profile in comparison to the naturally occurring and more common smooth variant. We show that genes involved in major biochemical cascades, including those involved in protein sorting, oxidative stress, and membrane transport, play a role in the wrinkly phenotype. Interestingly, only a few unique genes are specifically involved in macromolecule biosynthesis in the wrinkly phenotype, which underlies the importance of other pathways utilized for adaptation under the conditions in which Vibrio bacteria are producing this change in phenotype. These results provide the first comprehensive analysis of the complex form of genetic activation that underlies the diversity in morphologies of V. fischeri when switching between two different colony morphotypes, each representing a unique biofilm ecotype.IMPORTANCE The wrinkly bacterial colony phenotype has been associated with increased squid host colonization in V. fischeri The significance of our research is in identifying the genetic mechanisms that are responsible for heightened biofilm formation in V. fischeri This report also advances our understanding of gene regulation in V. fischeri and brings to the forefront a number of previously overlooked genetic networks. Several loci that were identified in this study were not previously known to be associated with biofilm formation in V. fischeri.

Insights into Antagonistic Interactions of Multidrug Resistant Bacteria in Mangrove Sediments from the South Indian State of Kerala

Antibiotic resistance is a global issue which is magnified by interspecies horizontal gene transfer. Understanding antibiotic resistance in bacteria in a natural setting is crucial to check whether they are multidrug resistant (MDR) and possibly avoid outbreaks. In this study, we have isolated several antibiotic-resistant bacteria (ARB) (n = 128) from the mangroves in Kerala, India. ARBs were distributed based on antibiotics (p = 1.6 × 10^-5). The 16S rRNA gene characterization revealed dominance by Bacillaceae (45%), Planococcaceae (22.5%), and Enterobacteriaceae (17.5%). A high proportion of the isolates were MDR (75%) with maximum resistance to methicillin (70%). Four isolates affiliated to plant-growth promoters, probiotics, food, and human pathogens were resistant to all antibiotics indicating the seriousness and prevalence of MDR. A significant correlation (R = 0.66; p = 2.5 × 10^-6) was observed between MDR and biofilm formation. Antagonist activity was observed in 62.5% isolates. Gram-positive isolates were more susceptible to antagonism (75.86%) than gram-negative (36.36%) isolates. Antagonism interactions against gram-negative isolates were lower (9.42%) when compared to gram-positive isolates (89.85%). Such strong antagonist activity can be harnessed for inspection of novel antimicrobial mechanisms and drugs. Our study shows that MDR with strong biofilm formation is prevalent in natural habitat and if acquired by deadly pathogens may create havoc in public health.

Does Ralstonia eutropha, rich in poly-β hydroxybutyrate (PHB), protect blue mussel larvae against pathogenic vibrios?

The natural amorphous polymer poly-β-hydroxybutyrate (PHB-A: lyophilized Ralstonia eutropha containing 75% PHB) was used as a biological agent to control bacterial pathogens of blue mussel (Mytilus edulis) larvae. The larvae were supplied with PHB-A at a concentration of 1 or 10 mg/L for 6 or 24 hr, followed by exposure to either the rifampicin-resistant pathogen Vibrio splendidus or Vibrio coralliilyticus at a concentration of 10⁵ CFU/ml. Larvae pretreated 6 hr with PHB-A (1 mg/L) survived a Vibrio challenge better relative to 24 hr pretreatment. After 96 hr of pathogen exposure, the survival of PHB-A-treated mussel larvae was 1.41- and 1.76-fold higher than the non-treated larvae when challenged with V. splendidus and V. coralliilyticus, respectively. Growth inhibition of the two pathogens at four concentrations of the monomer β-HB (1, 5, 25 and 125 mM) was tested in vitro in LB₃₅ medium, buffered at two different pH values (pH 7 and pH 8). The highest concentration of 125 mM significantly inhibited the pathogen growth in comparison to the lower levels. The effect of β-HB on the production of virulence factors in the tested pathogenic Vibrios revealed a variable pattern of responses.

Tools for Rapid Genetic Engineering of Vibrio fischeri

Vibrio fischeri is used as a model for a number of processes, including symbiosis, quorum sensing, bioluminescence, and biofilm formation. Many of these studies depend on generating deletion mutants and complementing them. Engineering such strains, however, is a time-consuming, multistep process that relies on cloning and subcloning. Here, we describe a set of tools that can be used to rapidly engineer deletions and insertions in the V. fischeri chromosome without cloning. We developed a uniform approach for generating deletions using PCR splicing by overlap extension (SOEing) with antibiotic cassettes flanked by standardized linker sequences. PCR SOEing of the cassettes to sequences up- and downstream of the target gene generates a DNA product that can be directly introduced by natural transformation. Selection for the introduced antibiotic resistance marker yields the deletion of interest in a single step. Because these cassettes also contain FRT (FLP recognition target) sequences flanking the resistance marker, Flp recombinase can be used to generate an unmarked, in-frame deletion. We developed a similar methodology and tools for the rapid insertion of specific genes at a benign site in the chromosome for purposes such as complementation. Finally, we generated derivatives of these tools to facilitate different applications, such as inducible gene expression and assessing protein production. We demonstrated the utility of these tools by deleting and inserting genes known or predicted to be involved in motility. While developed for V. fischeri strain ES114, we anticipate that these tools can be adapted for use in other V. fischeri strains and, potentially, other microbes.IMPORTANCEVibrio fischeri is a model organism for studying a variety of important processes, including symbiosis, biofilm formation, and quorum sensing. To facilitate investigation of these biological mechanisms, we developed approaches for rapidly generating deletions and insertions and demonstrated their utility using two genes of interest. The ease, consistency, and speed of the engineering is facilitated by a set of antibiotic resistance cassettes with common linker sequences that can be amplified by PCR with universal primers and fused to adjacent sequences using splicing by overlap extension and then introduced directly into V. fischeri, eliminating the need for cloning and plasmid conjugation. The antibiotic cassettes are flanked by FRT sequences, permitting their removal using Flp recombinase. We augmented these basic tools with a family of constructs for different applications. We anticipate that these tools will greatly accelerate mechanistic studies of biological processes in V. fischeri and potentially other Vibrio species.

Biofilm formation of hypermucoviscous and non-hypermucoviscous Klebsiella pneumoniae recovered from clinically affected African green monkey (Chlorocebus aethiops sabaeus)

In recent years, an emergent Klebsiella pneumoniae hypermucoviscous (HMV) phenotype has been associated with increased invasiveness and pathogenicity in primates. The HMV phenotype is characterized by different capsular serotypes, associated with several genes including the rmpA (regulator of mucoid phenotype) and magA (mucoviscosity-associated) genes. In African green monkeys (AGM) (Chlorocebus aethiops sabaeus) serotypes K1 and K5 have been implicated in fatal multisystemic abscesses. In order to better understand the epizootiology of this pathogen, the capacity of biofilm production of K. pneumoniae isolates presenting the HMV was compared to non-HMV isolates at three different temperatures (25, 30 and 37 °C). The results indicate that HMV and non-HMV isolates display similar capacity to form biofilms at the three different evaluated temperatures. Temperature appears to play a role in the formation of biofilms by K. pneumoniae presenting the HMV phenotype, where larger biofilms were formed at 37 °C than at 25 °C. Knowledge regarding local environmental sources of K. pneumoniae and the possible role of wildlife in the maintenance of this agent in the area is necessary to develop effective recommendations for the prevention and management of this disease in captive AGM populations.

Proteomic and metabolomic profiles demonstrate variation among free-living and symbiotic vibrio fischeri biofilms

Background

A number of bacterial species are capable of growing in various life history modes that enable their survival and persistence in both planktonic free-living stages as well as in biofilm communities. Mechanisms contributing to either planktonic cell or biofilm persistence and survival can be carefully delineated using multiple differential techniques (e.g., genomics and transcriptomics). In this study, we present both proteomic and metabolomic analyses of Vibrio fischeri biofilms, demonstrating the potential for combined differential studies for elucidating life-history switches important for establishing the mutualism through biofilm formation and host colonization.

Methods

The study used a metabolomics/proteomics or “meta-proteomics” approach, referring to the combined protein and metabolic data analysis that bridges the gap between phenotypic changes (planktonic cell to biofilm formation) with genotypic changes (reflected in protein/metabolic profiles). Our methods used protein shotgun construction, followed by liquid chromatography coupled with mass spectrometry (LC-MS) detection and quantification for both free-living and biofilm forming V. fischeri.

Results

We present a time-resolved picture of approximately 100 proteins (2D-PAGE and shotgun proteomics) and 200 metabolites that are present during the transition from planktonic growth to community biofilm formation. Proteins involved in stress response, DNA repair damage, and transport appeared to be highly expressed during the biofilm state. In addition, metabolites detected in biofilms correspond to components of the exopolysaccharide (EPS) matrix (sugars and glycerol-derived). Alterations in metabolic enzymes were paralleled by more pronounced changes in concentration of intermediates from the glycolysis pathway as well as several amino acids.

Conclusions

This combined analysis of both types of information (proteins, metabolites) has provided a more complete picture of the biochemical processes of biofilm formation and what determines the switch between the two life history strategies. The reported findings have broad implications for Vibrio biofilm ecology, and mechanisms for successful survival in the host and environment.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-015-0560-z) contains supplementary material, which is available to authorized users.

Biofilm formation of Francisella noatunensis subsp. orientalis

Francisella noatunensis subsp. orientalis (Fno) is an emergent fish pathogen in both marine and fresh water environments. The bacterium is suspected to persist in the environment even without the presence of a suitable fish host. In the present study, the influence of different abiotic factors such as salinity and temperature were used to study the biofilm formation of different isolates of Fno including intracellular growth loci C (iglC) and pathogenicity determinant protein A (pdpA) knockout strains. Finally, we compared the susceptibility of planktonic and biofilm to three disinfectants used in the aquaculture and ornamental fish industry, namely Virkon(®), bleach and hydrogen peroxide. The data indicates that Fno is capable of producing biofilms within 24 h where both salinity as well as temperature plays a role in the growth and biofilm formation of Fno. Mutations in the iglC or pdpA, both known virulence factors, do not appear to affect the capacity of Fno to produce biofilms, and the minimum inhibitory concentration, and minimum biocidal concentration for the three disinfectants were lower than the minimum biofilm eradication concentration values. This information needs to be taken into account if trying to eradicate the pathogen from aquaculture facilities or aquariums.

Microbial experimental evolution as a novel research approach in the Vibrionaceae and squid-Vibrio symbiosis

The Vibrionaceae are a genetically and metabolically diverse family living in aquatic habitats with a great propensity toward developing interactions with eukaryotic microbial and multicellular hosts (as either commensals, pathogens, and mutualists). The Vibrionaceae frequently possess a life history cycle where bacteria are attached to a host in one phase and then another where they are free from their host as either part of the bacterioplankton or adhered to solid substrates such as marine sediment, riverbeds, lakebeds, or floating particulate debris. These two stages in their life history exert quite distinct and separate selection pressures. When bound to solid substrates or to host cells, the Vibrionaceae can also exist as complex biofilms. The association between bioluminescent Vibrio spp. and sepiolid squids (Cephalopoda: Sepiolidae) is an experimentally tractable model to study bacteria and animal host interactions, since the symbionts and squid hosts can be maintained in the laboratory independently of one another. The bacteria can be grown in pure culture and the squid hosts raised gnotobiotically with sterile light organs. The partnership between free-living Vibrio symbionts and axenic squid hatchlings emerging from eggs must be renewed every generation of the cephalopod host. Thus, symbiotic bacteria and animal host can each be studied alone and together in union. Despite virtues provided by the Vibrionaceae and sepiolid squid-Vibrio symbiosis, these assets to evolutionary biology have yet to be fully utilized for microbial experimental evolution. Experimental evolution studies already completed are reviewed, along with exploratory topics for future study.

Ecological diversification of Vibrio fischeri serially passaged for 500 generations in novel squid host Euprymna tasmanica

Vibrio fischeri isolated from Euprymna scolopes (Cephalopoda: Sepiolidae) was used to create 24 lines that were serially passaged through the non-native host Euprymna tasmanica for 500 generations. These derived lines were characterized for biofilm formation, swarming motility, carbon source utilization, and in vitro bioluminescence. Phenotypic assays were compared between "ES" (E. scolopes) and "ET" (E. tasmanica) V. fischeri wild isolates to determine if convergent evolution was apparent between E. tasmanica evolved lines and ET V. fischeri. Ecological diversification was observed in utilization of most carbon sources examined. Convergent evolution was evident in motility, biofilm formation, and select carbon sources displaying hyperpolymorphic usage in V. fischeri. Convergence in bioluminescence (a 2.5-fold increase in brightness) was collectively evident in the derived lines relative to the ancestor. However, dramatic changes in other properties--time points and cell densities of first light emission and maximal light output and emergence of a lag phase in growth curves of derived lines--suggest that increased light intensity per se was not the only important factor. Convergent evolution implies that gnotobiotic squid light organs subject colonizing V. fischeri to similar selection pressures. Adaptation to novel hosts appears to involve flexible microbial metabolism, establishment of biofilm and swarmer V. fischeri ecotypes, and complex changes in bioluminescence. Our data demonstrate that numerous alternate fitness optima or peaks are available to V. fischeri in host adaptive landscapes, where novel host squids serve as habitat islands. Thus, V. fischeri founder flushes occur during the initiation of light organ colonization that ultimately trigger founder effect diversification.

Predation response of Vibrio fischeri biofilms to bacterivorus protists

Vibrio fischeri proliferates in a sessile, stable community known as a biofilm, which is one alternative survival strategy of its life cycle. Although this survival strategy provides adequate protection from abiotic factors, marine biofilms are still susceptible to grazing by bacteria-consuming protozoa. Subsequently, grazing pressure can be controlled by certain defense mechanisms that confer higher biofilm antipredator fitness. In the present work, we hypothesized that V. fischeri exhibits an antipredator fitness behavior while forming biofilms. Different predators representing commonly found species in aquatic populations were examined, including the flagellates Rhynchomonas nasuta and Neobodo designis (early biofilm feeders) and the ciliate Tetrahymena pyriformis (late biofilm grazer). V. fischeri biofilms included isolates from both seawater and squid hosts (Euprymna and Sepiola species). Our results demonstrate inhibition of predation by biofilms, specifically, isolates from seawater. Additionally, antiprotozoan behavior was observed to be higher in late biofilms, particularly toward the ciliate T. pyriformis; however, inhibitory effects were found to be widespread among all isolates tested. These results provide an alternative explanation for the adaptive advantage and persistence of V. fischeri biofilms and provide an important contribution to the understanding of defensive mechanisms that exist in the out-of-host environment.

Multiple Vibrio fischeri genes are involved in biofilm formation and host colonization

Biofilms are increasingly recognized as being the predominant form for survival for most bacteria in the environment. The successful colonization of Vibrio fischeri in its squid host Euprymna tasmanica involves complex microbe-host interactions mediated by specific genes that are essential for biofilm formation and colonization. Here, structural and regulatory genes were selected to study their role in biofilm formation and host colonization. We have mutated several genes (pilT, pilU, flgF, motY, ibpA and mifB) by an insertional inactivation strategy. The results demonstrate that structural genes responsible for synthesis of type IV pili and flagella are crucial for biofilm formation and host infection. Moreover, regulatory genes affect colony aggregation by various mechanisms, including alteration of synthesis of transcriptional factors and regulation of extracellular polysaccharide production. These results reflect the significance of how genetic alterations influence communal behavior, which is important in understanding symbiotic relationships.