Persistence of functional microbiota composition across generations

Holobionts are defined as a host and its microbiota, however, only a fraction of the bacteria are inherited vertically and thus coevolve with the host. The "it's the song, not the singer" theory proposes that functional traits, instead of taxonomical microbiota composition, could be preserved across generations if interspecies interaction patterns perpetuate themselves. We tested conservation of functional composition across generations using zooplankton, mosquito, and plant datasets. Then, we tested if there is a change of functional microbiota composition over time within a generation in human datasets. Finally, we simulated microbiota communities to investigate if (pairwise) interactions can lead to multiple stable community compositions. Our results suggest that the vertically transmitted microbiota starts a predictable change of functions performed by the microbiota over time, whose robustness depends on the arrival of diverse migrants. This succession culminates in a stable functional composition state. The results suggest that the host-microbiota interaction and higher order interactions in general have an important contribution to the robustness of the final community. If the proposed mechanism proves to be valid for a diverse array of host species, this would support the concept of holobionts being used as units of selection, including animal breeding, suggesting this has a wider applicability.

Genotypic variation in an ecologically important parasite is associated with host species, lake and spore size

Genetic variation in parasites has important consequences for host–parasite interactions. Prior studies of the ecologically important parasite Metschnikowia bicuspidata have suggested low genetic variation in the species. Here, we collected M. bicuspidata from two host species (Daphnia dentifera and Ceriodaphnia dubia) and two regions (Michigan and Indiana, USA). Within a lake, outbreaks tended to occur in one host species but not the other. Using microsatellite markers, we identified six parasite genotypes grouped within three distinct clades, one of which was rare. Of the two main clades, one was generally associated with D. dentifera, with lakes in both regions containing a single genotype. The other M. bicuspidata clade was mainly associated with C. dubia, with a different genotype dominating in each region. Despite these associations, both D. dentifera- and C. dubia-associated genotypes were found infecting both hosts in lakes. However, in lab experiments, the D. dentifera-associated genotype infected both D. dentifera and C. dubia, but the C. dubia-associated genotype, which had spores that were approximately 30% smaller, did not infect D. dentifera. We hypothesize that variation in spore size might help explain patterns of cross-species transmission. Future studies exploring the causes and consequences of variation in spore size may help explain patterns of infection and the maintenance of genotypic diversity in this ecologically important system.

Grazing pressure-induced shift in planktonic bacterial communities with the dominance of acIII-A1 actinobacterial lineage in soda pans

Astatic soda pans of the Pannonian Steppe are unique environments with respect to their multiple extreme physical and chemical characteristics (high daily water temperature fluctuation, high turbidity, alkaline pH, salinity, polyhumic organic carbon concentration, hypertrophic state and special ionic composition). However, little is known about the seasonal dynamics of the bacterial communities inhabiting these lakes and the role of environmental factors that have the main impact on their structure. Therefore, two soda pans were sampled monthly between April 2013 and July 2014 to reveal changes in the planktonic community. By late spring in both years, a sudden shift in the community structure was observed, the previous algae-associated bacterial communities had collapsed, resulting the highest ratio of Actinobacteria within the bacterioplankton (89%, with the dominance of acIII-A1 lineage) ever reported in the literature. Before these peaks, an extremely high abundance (> 10,000 individuum l-1) of microcrustaceans (Moina brachiata and Arctodiaptomus spinosus) was observed. OTU-based statistical approaches showed that in addition to algal blooms and water-level fluctuations, zooplankton densities had the strongest effect on the composition of bacterial communities. In these extreme environments, this implies a surprisingly strong, community-shaping top-down role of microcrustacean grazers.

Mycosporine-Like Amino Acids (MAAs) in Zooplankton

Organisms have different adaptations to avoid damage from ultraviolet radiation and one such adaptation is the accumulation of mycosporine-like amino acids (MAAs). These compounds are common in aquatic taxa but a comprehensive review is lacking on their distribution and function in zooplankton. This paper shows that zooplankton MAA concentrations range from non-detectable to ~13 µg mgDW⁻¹. Copepods, rotifers, and krill display a large range of concentrations, whereas cladocerans generally do not contain MAAs. The proposed mechanisms to gain MAAs are via ingestion of MAA-rich food or via symbiotic bacteria providing zooplankton with MAAs. Exposure to UV-radiation increases the concentrations in zooplankton both via increasing MAA concentrations in the phytoplankton food and due to active accumulation. Concentrations are generally low during winter and higher in summer and females seem to deposit MAAs in their eggs. The concentrations of MAAs in zooplankton tend to increase with altitude but only up to a certain altitude suggesting some limitation for the uptake. Shallow and UV-transparent systems tend to have copepods with higher concentrations of MAAs but this has only been shown in a few species. A high MAA concentration has also been shown to lead to lower UV-induced mortality and an overall increased fitness. While there is a lot of information on MAAs in zooplankton we still lack understanding of the potential costs and constraints for accumulation. There is also scarce information in some taxa such as rotifers as well as from systems in tropical, sub(polar) areas as well as in marine systems in general.

Attachment and antimicrobial susceptibility of bacterial associates of zooplanktonic copepod: Lesson for environmental safety

The present study emphasizes on the antimicrobial susceptibility of different bacterial strains isolated from the external body surface of a commonly found zooplanktonic copepod (Heliodiaptomus viduus, Gurney, 1916) inhabiting both in fresh and brackish water bodies of Midnapore (West and East) Districts, West Bengal, India. Out of 62 bacterial isolated strains, 38 isolates were identified as Gram-positive while the remaining 24 isolates were found to be Gram-negative. Antimicrobial properties of all those bacterial strains were determined by Vitek 2 compact system using minimum inhibitory concentration (MIC) values. All isolated bacterial strains had exhibited differential susceptibilities against some selected antibiotics. Field Emission Scanning Electron Microscope (FE-SEM) analysis revealed the considerable association of bacteria on the cuticular body parts of the studied zooplankton. The outcomes of the present research are expected to enable health professionals in identifying two major problems -1) bacterial association with zooplankton which is so far mostly considered as a novel source of food for fish in aquatic ecosystems. 2) Selection of antibiotics as treatment measure because of the pathogenic effects of zooplankton associated bacteria on human being. This unattended arena of research is also supposed to evoke a new dimension not only because of bacteria-zooplankton interactions but also on undertaking of judicious strategies to find out proper ways and means to make the surface water suitable for the utilization by the common peoples (minimising bacterial contamination) in the context of human health and environmental safety.

Persistence of fecal indicator bacteria associated with zooplankton in a tropical estuary-west coast of India

In a study carried out during 2014, bacteria associated with zooplankton in the Zuari estuary were three to four orders of magnitude higher in abundance than in seawater. The live zooplankton carried much more bacterial load compared with the carcasses, and the fecal pellets harbored the highest density of bacteria, i.e., 8 × 10¹³ CFU cm^-3. The diversity of bacteria was higher in live zooplankton and also in seawater. But the activity of the zooplankton-associated bacteria was much higher compared with the free-living ones. Most of the associated bacteria belonged to the genus Enterobacter, Pseudomonas, Aeromonas, and Bacillus. In growth experiments, Aeromonas and Bacillus were found to have lower salinity optima than Enterobacter (20 psu) and Vibrio and Pseudomonas (normal seawater salinity). Better growth of bacteria was observed in the medium containing the diatom Chaetoceros sp. than Navicula sp. Bacterial isolates were also able to survive in oligotrophic conditions and produce optimum biomass in 2 days at salinity 5 psu, but in freshwater, the bacteria took a week's time to attain the optima. At salinities 0-35, the bacteria survived even for 3 months without nutrient addition, indicating resilience in these bacteria and mechanisms to persist in the estuaries even in adverse conditions.

Chromulinavorax destructans, a pathogen of microzooplankton that provides a window into the enigmatic candidate phylum Dependentiae

Members of the major candidate phylum Dependentiae (a.k.a. TM6) are widespread across diverse environments from showerheads to peat bogs; yet, with the exception of two isolates infecting amoebae, they are only known from metagenomic data. The limited knowledge of their biology indicates that they have a long evolutionary history of parasitism. Here, we present Chromulinavorax destructans (Strain SeV1) the first isolate of this phylum to infect a representative from a widespread and ecologically significant group of heterotrophic flagellates, the microzooplankter Spumella elongata (Strain CCAP 955/1). Chromulinavorax destructans has a reduced 1.2 Mb genome that is so specialized for infection that it shows no evidence of complete metabolic pathways, but encodes an extensive transporter system for importing nutrients and energy in the form of ATP from the host. Its replication causes extensive reorganization and expansion of the mitochondrion, effectively surrounding the pathogen, consistent with its dependency on the host for energy. Nearly half (44%) of the inferred proteins contain signal sequences for secretion, including many without recognizable similarity to proteins of known function, as well as 98 copies of proteins with an ankyrin-repeat domain; ankyrin-repeats are known effectors of host modulation, suggesting the presence of an extensive host-manipulation apparatus. These observations help to cement members of this phylum as widespread and diverse parasites infecting a broad range of eukaryotic microbes.

Little is known about the biology of bacteria in the candidate phylum Dependentiae, despite being widespread in nature. Here, we describe a novel isolate of this phylum, Chromulinavorax destructans, which infects an abundant aquatic predatory protist, Spumella elongata. Chromulinavorax destructans is an obligate intracellular parasite, forgoes binary fission and replicates surrounded by the host mitochondrion. The genome of C. destructans encodes no detectable complete metabolic pathways and instead contains extensive transporter systems to import metabolites and even energy in the form of ATP from the host. We also found a surprising number of genes in the C. destructans genome encoding putative host modifying proteins that might be responsible for the extensive host reorganization. Phylogenetic analysis showed that C. destructans is distantly related to intracellular pathogens and symbionts of unrelated amoebae. Hence, Chromulinavorax destructans provides new insights into the biology of a widespread but largely unknown phylum of bacteria. These results imply that members of the Dependentiae are pathogens of diverse aquatic protists and are therefore likely important players in aquatic ecosystems.

Jellyfish-Associated Microbiome in the Marine Environment: Exploring Its Biotechnological Potential

Despite accumulating evidence of the importance of the jellyfish-associated microbiome to jellyfish, its potential relevance to blue biotechnology has only recently been recognized. In this review, we emphasize the biotechnological potential of host⁻microorganism systems and focus on gelatinous zooplankton as a host for the microbiome with biotechnological potential. The basic characteristics of jellyfish-associated microbial communities, the mechanisms underlying the jellyfish-microbe relationship, and the role/function of the jellyfish-associated microbiome and its biotechnological potential are reviewed. It appears that the jellyfish-associated microbiome is discrete from the microbial community in the ambient seawater, exhibiting a certain degree of specialization with some preferences for specific jellyfish taxa and for specific jellyfish populations, life stages, and body parts. In addition, different sampling approaches and methodologies to study the phylogenetic diversity of the jellyfish-associated microbiome are described and discussed. Finally, some general conclusions are drawn from the existing literature and future research directions are highlighted on the jellyfish-associated microbiome.

Metagenomic insights into zooplankton-associated bacterial communities

Zooplankton and microbes play a key role in the ocean's biological cycles by releasing and consuming copious amounts of particulate and dissolved organic matter. Additionally, zooplankton provide a complex microhabitat rich in organic and inorganic nutrients in which bacteria thrive. In this study, we assessed the phylogenetic composition and metabolic potential of microbial communities associated with crustacean zooplankton species collected in the North Atlantic. Using Illumina sequencing of the 16S rRNA gene, we found significant differences between the microbial communities associated with zooplankton and those inhabiting the surrounding seawater. Metagenomic analysis of the zooplankton-associated microbial community revealed a highly specialized bacterial community able to exploit zooplankton as microhabitat and thus, mediating biogeochemical processes generally underrepresented in the open ocean. The zooplankton-associated bacterial community is able to colonize the zooplankton's internal and external surfaces using a large set of adhesion mechanisms and to metabolize complex organic compounds released or exuded by the zooplankton such as chitin, taurine and other complex molecules. Moreover, the high number of genes involved in iron and phosphorus metabolisms in the zooplankton-associated microbiome suggests that this zooplankton-associated bacterial community mediates specific biogeochemical processes (through the proliferation of specific taxa) that are generally underrepresented in the ambient waters.

Distribution and antimicrobial susceptibility of Vibrio species associated with zooplankton in coastal area of Korea

Vibrio parahaemolyticus and V. vulnificus are the most common pathogens causing seafood-borne illnesses in Korea. This study determines the abundance and antimicrobial resistance of pathogenic Vibrio species in seawater and zooplankton samples from the Geoje Island coast in Korea, which is an important area for coastal fisheries, the fishing industry, and tourism. The two Vibrio species were detected more in mesozooplankton samples than in seawater samples. V. parahaemolyticus isolates showed greater resistance than those of V. vulnificus for antimicrobials. Of V. parahaemolyticus isolates, 93.3% exhibited resistance to three or more antimicrobial agents. Conversely, more than 80% of V. vulnificus isolates showed susceptibility to all antimicrobials examined, with the exception of rifampicin. Our findings show that strong antimicrobial resistance of V. parahaemolyticus in the surveyed area was exposed to conventionally used antibiotics, therefore necessitating proper surveillance programs for the monitoring of antimicrobial resistance patterns in seawater bodies and aquatic animals.

The interaction between cyanobacteria and zooplankton in a more eutrophic world

As blooms of cyanobacteria expand and intensify in freshwater systems globally, there is increasing interest in their ecological effects. In addition to being public health hazards, cyanobacteria have long been considered a poor quality food for key zooplankton grazers that link phytoplankton to higher trophic levels. While past laboratory studies have found negative effects of nutritional constraints and defensive traits (i.e., toxicity and colonial or filamentous morphology) on the fitness of large generalist grazers (i.e., Daphnia), cyanobacterial blooms often co-exist with high biomass of small-bodied zooplankton in nature. Indeed, recent studies highlight the remarkable diversity and flexibility in zooplankton responses to cyanobacterial prey. Reviewed here are results from a wide range of laboratory and field experiments examining the interaction of cyanobacteria and a diverse zooplankton taxa including cladocerans, copepods, and heterotrophic protists from temperate to tropical freshwater systems. This synthesis shows that longer exposure to cyanobacteria can shift zooplankton communities toward better-adapted species, select for more tolerant genotypes within a species, and induce traits within the lifetime of individual zooplankton. In turn, the function of bloom-dominated plankton ecosystems, the coupling between primary producers and grazers, the stability of blooms, and the potential to use top down biomanipulation for controlling cyanobacteria depend largely on the species, abundance, and traits of interacting cyanobacteria and zooplankton. Understanding the drivers and consequences of zooplankton traits, such as physiological detoxification and selective vs. generalist grazing behavior, are therefore of major importance for future studies. Ultimately, co-evolutionary dynamics between cyanobacteria and their grazers may emerge as a critical regulator of blooms.

Inactivation mechanism of chlorination in Escherichia coli internalized in Limnoithona sinensis and Daphnia magna

Zooplankton may harbor microorganisms in the aquatic environment, thus protecting them from disinfection during drinking water treatment. However, few studies have evaluated the protective effect of internalization by zooplankton against bacterial disinfection. In this study, we investigated the role of zooplankton (Limnoithona sinensis and Daphnia magna) as a refuge for ingested bacteria against inactivation by chlorination. Only 30% of chlorine reached the internalized bacteria inside the digestive tract of zooplankton. However, this was sufficient to achieve 1.4 log inactivation of internalized Escherichia coli in L. sinensis and 1.2 log inactivation in D. magna at Ct values of 80 mg min/L. Inactivation of internalized bacteria was achieved through the active transfer of free chlorine in the bulk water into the zooplankton digestive tract during grazing activity. D. magna was more sensitive to hypochlorous acid than L. sinensis, and its grazing behavior was inhibited during the inactivation experiment.

The role of microorganisms in a planktonic food web of a floodplain lake

Food webs include complex ecological interactions that define the flow of matter and energy, and are fundamental in understanding the functioning of an ecosystem. Temporal variations in the densities of communities belonging to the planktonic food web (i.e., microbial: bacteria, flagellate, and ciliate; and grazing: zooplankton and phytoplankton) were investigated, aiming to clarify the interactions between these organisms and the dynamics of the planktonic food web in a floodplain lake. We hypothesized that hydrological pulse determines the path of matter and energy flow through the planktonic food web of this floodplain lake. Data were collected monthly from March 2007 to February 2008 at three different sites in Guaraná Lake (Mato Grosso do Sul State, Brazil). The path analysis provided evidence that the dynamics of the planktonic food web was strongly influenced by the hydrological pulse. The high-water period favored interactions among the organisms of the microbial loop, rather than their relationships with zooplankton and phytoplankton. Therefore, in this period, the strong interaction among the organisms of the grazing food chain suggests that the microbial loop functions as a sink of matter and energy. In turn, in the low-water period, higher primary productivity appeared to favor different interactions between the components of the grazing food chain and microorganisms, which would function as a link to the higher trophic levels.

Predation and transport of persistent pathogens in GAC and slow sand filters: a threat to drinking water safety?

Zooplankton has been shown to transport internalized pathogens throughout engineered drinking water systems. In this study, experimental measurements from GAC and SSF filtration tests using high influent concentrations of Cryptosporidium (1.3 × 10(6) and 3.3 × 10(4) oocysts L(-1)) and Giardia (4.8 × 10(4) cysts L(-1)) are presented and compared. A predation and transport conceptual model was developed to extrapolate these results to environmental conditions of typical (oo)cyst concentrations in surface water in order to predict concentrations of internalized (oo)cysts in filtered water. Pilot test results were used to estimate transport and survival ratios of internalized (oo)cysts following predation by rotifers in the filter beds. Preliminary indications of lower transport and survival ratios in SSF were found as compared with GAC filters. A probability of infection due to internalized (oo)cysts in filtered water was calculated under likeliest environmental conditions and under a worst-case scenario. Estimated risks under the likeliest environmental scenario were found to fall below the tolerable risk target of 10(-4) infections per person per year. A discussion is presented on the health significance of persistent pathogens that are internalized by zooplankton during granular filtration processes and released into treated water.

Ocean net heat flux influences seasonal to interannual patterns of plankton abundance

Changes in the net heat flux (NHF) into the ocean have profound impacts on global climate. We analyse a long-term plankton time-series and show that the NHF is a critical indicator of ecosystem dynamics. We show that phytoplankton abundance and diversity patterns are tightly bounded by the switches between negative and positive NHF over an annual cycle. Zooplankton increase before the transition to positive NHF in the spring but are constrained by the negative NHF switch in autumn. By contrast bacterial diversity is decoupled from either NHF switch, but is inversely correlated (r = −0.920) with the magnitude of the NHF. We show that the NHF is a robust mechanistic tool for predicting climate change indicators such as spring phytoplankton bloom timing and length of the growing season.

Trophic transfer of microcystins through the lake pelagic food web: evidence for the role of zooplankton as a vector in fish contamination

An in situ study was performed to investigate the role of zooplankton as a vector of microcystins (MCs) from Planktothrix rubescens filaments to fish during a metalimnic bloom of P. rubescens in Lake Hallwil (Switzerland). The concentrations of MCs in P. rubescens and various zooplanktonic taxa (filter-feeders and predators) were assessed in different water strata (epi-, meta- and hypolimnion) using replicated sampling over a 24-hour survey. The presence of P. rubescens in the gut content of various zooplanktonic taxa (Daphnia, Bosmina and Chaoborus) was verified by targeting the cyanobacterial nucleic acids (DNA). These results highlighted that cyanobacterial cells constitute a part of food resource for herbivorous zooplanktonic taxa during metalimnic bloom periods. Furthermore, presence of MCs in Chaoborus larvae highlighted the trophic transfer of MCs between herbivorous zooplankton and their invertebrate predators. Our results suggest that zooplanktonic herbivores by diel vertical migration (DVM) act as vectors of MCs by encapsulating grazed cyanobacteria. As a consequence, they largely contribute to the contamination of zooplanktonic predators, and in fine of zooplanktivorous whitefish. Indeed, we estimated the relative contribution of three preys of the whitefish (i.e. Daphnia, Bosmina and Chaoborus) to diet contamination. We showed that Chaoborus and Daphnia were the highest contributor as MC vectors in the whitefish diet (74.6 and 20.5% of MC-LR equivalent concentrations, respectively). The transfer of MCs across the different trophic compartments follows complex trophic pathways involving various trophic levels whose relative importance in fish contamination might vary at daily and seasonal scale.

Association of bacteria with marine invertebrates: implications for ballast water management

Bacteria associated with plankton are of importance in marine bioinvasions and the implementation of ship's ballast water treatment technologies. In this study, epibiotic and endobiotic bacteria associated with zooplankton, including barnacle nauplii, veliger larvae, and adults of the copepod Oithona sp., were characterized and quantified. Barnacle nauplius and veliger larva harbored ~4.4 × 10(5)cells ind(-1) whereas Oithona sp. had 8.8 × 10(5)cells ind(-1). Computation of bacterial contribution based on biovolume indicated that despite being the smallest zooplankton tested, veliger larvae harbored the highest number of bacteria, while barnacle nauplii, the largest of the zooplankton, tested in terms of volume contributed the least. Pulverization of zooplankton led to an increase in bacterial numbers; for example, Vibrio cholerae, which was initially 3.5 × 10(3), increased to 5.4 × 10(5)CFU g(-1); Escherichia coli increased from 5.0 × 10(2) to 1.3 × 10(4)CFU g(-1); and Streptococcus faecalis increased from 2.1 × 10(2) to 2.5 × 10(5)CFU g(-1), respectively. Pulverized zooplankton was aged in the dark to assess the contribution of bacteria from decaying debris. Aging of pulverized zooplankton led to emergence of Chromobacterium violaceum, which is an opportunistic pathogen in animals and humans.

Preliminary studies on the association between zooplankton and the stramenopilan fungi, aplanochytrids

The relationship of the marine heterokont stramenopilan protists, the aplanochytrids, with the zooplankton was studied in coastal waters. The aplanochytrids were fed to the zooplankton specimens and observed for grazing by two different approaches: [1] using fluorescently-labeled prey approach and [2] using internal transcribed spacer-based molecular probe and in situ hybridization approach. The aplanochytrid cells were detected in the guts as well as fecal pellets of the zooplankton, thus serving as prey to them. Aplanochytrids were consistently isolated from zooplankton specimens. The isolates did not produce a wide array of enzymes, implicating that they may not play a major role in degradation of zooplankton exoskeleton. They were found to produce only protease considerably and sometimes lipase too. The amplified rDNA restriction analysis showed similar patterns, suggesting that most of the isolates might be same strains of Aplanochytrium spp. The existence of aplanochytrids with the zooplankton in marine waters points towards their probable association either as predator-prey or as commensalistic rather than saprophytic type of association.

Long-term characterization of free-living and particle-associated bacterial communities in Lake Tiefwaren reveals distinct seasonal patterns

Seasonal changes in environmental conditions have a strong impact on microbial community structure and dynamics in aquatic habitats. To better elucidate the response of bacterial communities to environmental changes, we have measured a large variety of limnetic variables and investigated bacterial community composition (BCC) and dynamics over seven consecutive years between 2003 and 2009 in mesotrophic Lake Tiefwaren (NE Germany). We separated between free-living (FL, >0.2, <5.0 μm) and particle-associated (PA, >5.0 μm) bacteria to account for different bacterial lifestyles and to obtain a higher resolution of the microbial diversity. Changes in BCC were studied by DGGE based on PCR-amplified 16S rRNA gene fragments. Sequencing of DGGE bands revealed that ca. 70 % of all FL bacteria belonged to the Actinobacteria, whereas PA bacteria were dominated by Cyanobacteria (43 %). FL communities were generally less diverse and rather stable over time compared to their PA counterpart. Annual changes in reoccurring seasonal patterns of dominant freshwater bacteria were supported by statistical analyses, which revealed several significant correlations between DGGE profiles and various environmental variables, e.g. temperature and nutrients. Overall, FL bacteria were generally less affected by environmental changes than members of the PA fraction. Close association of PA bacteria with phytoplankton and zooplankton suggests a tight coupling of PA bacteria to organisms of higher trophic levels. Our results indicate substantial differences in bacterial lifestyle of pelagic freshwater bacteria, which are reflected by contrasting seasonal dynamics and relationships to a number of environmental variables.

Interaction of Vibrio cholerae non-O1/non-O139 with copepods, cladocerans and competing bacteria in the large alkaline lake Neusiedler See, Austria

Vibrio cholerae is a human pathogen and natural inhabitant of aquatic environments. Serogroups O1/O139 have been associated with epidemic cholera, while non-O1/non-O139 serogroups usually cause human disease other than classical cholera. V. cholerae non-O1/non-O139 from the Neusiedler See, a large Central European lake, have caused ear and wound infections, including one case of fatal septicaemia. Recent investigations demonstrated rapid planktonic growth of V. cholerae non-O1/non-O139 and correlation with zooplankton biomass. The aim of this study was to elucidate the interaction of autochthonous V. cholerae with two dominant crustacean zooplankton species in the lake and investigate the influence of the natural bacterial community on this interaction. An existing data set was evaluated for statistical relationships between zooplankton species and V. cholerae and co-culture experiments were performed in the laboratory. A new fluorescence in situ hybridisation protocol was applied for quantification of V. cholerae non-O1/non-O139 cells, which significantly reduced analysis time. The experiments clearly demonstrated a significant relationship of autochthonous V. cholerae non-O1/non-O139 with cladocerans by promoting growth of V. cholerae non-O1/non-O139 in the water and on the surfaces of the cladocerans. In contrast, copepods had a negative effect on the growth of V. cholerae non-O1/non-O139 via competing bacteria from their surfaces. Thus, beside other known factors, biofilm formation by V. cholerae on crustacean zooplankton appears to be zooplankton taxon specific and may be controlled by the natural bacterial community.

A colonization factor links Vibrio cholerae environmental survival and human infection

Many bacteria that cause diseases must be able to survive inside and outside the host. Attachment to and colonization of abiotic or biotic surfaces is a common mechanism by which various microorganisms enhance their ability to survive in diverse environments. Vibrio cholerae is a Gram-negative aquatic bacillus that is often found in the environment attached to the chitinous exoskeletons of zooplankton. It has been suggested that attachment to zooplankton enhances environmental survival of Vibrio spp., probably by providing both an abundant source of carbon and nitrogen and protection from numerous environmental challenges. On ingestion by humans, some serogroups of V. cholerae cause the diarrhoeal disease cholera. The pathophysiology of cholera is a result of the effects of cholera toxin on intestinal epithelial cells. For sufficient quantities of cholera toxin to reach the intestinal epithelium and to produce clinical symptoms, colonization of the small bowel must occur. Because most V. cholerae do not colonize humans, but all probably require strategies for survival in the environment, we considered that colonization factors selected for in the environment may be the same as those required for intestinal colonization of humans. In support of this hypothesis, here we have identified a single protein required for efficient intestinal colonization that mediates attachment to both zooplankton and human epithelial cells by binding to a sugar present on both surfaces.

Trophic transfer of cyanobacterial toxins from zooplankton to planktivores: consequences for pike larvae and mysid shrimps

The aim of this study was to evaluate the potentially harmful effects of zooplankton preexposed to cyanobacteria on two planktivorous animals: a fish larva (pike, Esox lucius) and a mysid shrimp (Neomysis integer). The planktivores were fed zooplankton from a natural community that had been preexposed to cell-free extract or to purified toxin (nodularin) of the cyanobacterium Nodularia spumigena, and the growth, feeding, and pellet production of the planktivores, as well as the toxin content of the pellets, were measured. In addition, radiolabeled nodularin ((3)H-dihydronodularin) was used in separate experiments to measure the vector transfer of nodularin from zooplankton to their predators. During 11-day exposures, dissolved nodularin was transferred to pike larvae and N. integer via zooplankton at very low rates of accumulation. Treatment with N. spumigena extract decreased the ingestion and feces production rates of pike larvae. With purified nodularin alone, no such effect could be observed. No effect on molting cycle length, fecal pellet production, C:N ratio, or growth of N. integer was detected. The results suggest that dissolved cyanobacterial toxins released during bloom decay can have a negative impact on feeding and, hence, on the growth of fish larvae via zooplankton, even without direct contact between cyanobacteria and the fish.

[Spatial and biogeographic characterization of macroalgal assemblages from Bahía del Rincón, Baja California Sur, Mexico]

Macroalgal studies in Baja California Sur have dealt mainly with occurrence and seasonality, but some areas are poorly known even for these basic data. Bahia del Rincón-La Rivera is an important high-productivity fisheries area where coastal infrastructure development is under way. A spatial characterization of the marine flora from Bahia del Rincón-La Rivera was done by intensive sampling at different depths and localities with skin and SCUBA diving. At least 500 m2 were surveyed in each site. Additionally. quantitative sampling was done in ten random 25 cm2 quadrates per site. In the intertidal section, density and cover estimates were used. We also investigated the historical records and geographical affinities. A total of 72 species were identified (most were red algae: 62%). We found no general trend in the biogeographical affinities, which varied with each taxonomic group. Most brown algae species were tropical-endemic; red algae temperate-cosmopolite and green algae tropical-cosmopolite. In the spatial assemblage structure we found a high similarity between the intertidal areas, but a low similarity in shallow or deeper areas (3-5 m). This pattern was the same when we compared the abundance of the main species. We suggest that there are significant spatial differences in recruitment and development of the assemblages in relation to vertical distribution (depth) and position along the shore. There is a clear-cut Gelidium-Jania belt in the intertidal zone and a Padina-Dictyota belt below the low tide. Sporadic and year-round species occur in the intertidal zone, annual and perennial species below the low tide line. Sites differ in recruitment and this affects the abundance of other species (such as coraline and Caulerpa species). Temperature and sedimentation affect seasonality, but community structure is relatively constant throughout the year.

Adhesion of Enterococcus faecalis in the nonculturable state to plankton is the main mechanism responsible for persistence of this bacterium in both lake and seawater

The presence of enterococci in lake and seawater in an 18-month survey comparing molecular (PCR and quantitative PCR) and culture methods was evaluated, as well as the possibility that zooplankton could act as reservoirs for enterococci. Samples of both water and zooplankton were collected monthly from a Lake Garda site and an Adriatic Sea site. In lake water, the positive samples numbered 13 of 54 (24%) by culture and 32 of 54 (59%) when PCR was applied. In seawater, they numbered 0 of 51 by culture and 18 of 51 (35%) by PCR. Enterococci were found either totally bound to plankton or totally in water, depending on the presence or absence of plankton, respectively. These results clearly indicate that the PCR assay is a powerful tool for detecting fecal indicators and pathogens in the environment, thus providing a much more sensitive method than culture.

Viable but nonculturable Vibrio cholerae O1 in the aquatic environment of Argentina

In Argentina, as in other countries of Latin America, cholera has occurred in an epidemic pattern. Vibrio cholerae O1 is native to the aquatic environment, and it occurs in both culturable and viable but nonculturable (VNC) forms, the latter during interepidemic periods. This is the first report of the presence of VNC V. cholerae O1 in the estuarine and marine waters of the Rio de la Plata and the Argentine shelf of the Atlantic Ocean, respectively. Employing immunofluorescence and PCR methods, we were able to detect reservoirs of V. cholerae O1 carrying the virulence-associated genes ctxA and tcpA. The VNC forms of V. cholerae O1 were identified in samples of water, phytoplankton, and zooplankton; the latter organisms were mainly the copepods Acartia tonsa, Diaptomus sp., Paracalanus crassirostris, and Paracalanus parvus. We found that under favorable conditions, the VNC form of V. cholerae can revert to the pathogenic, transmissible state. We concluded that V. cholerae O1 is a resident of Argentinean waters, as has been shown to be the case in other geographic regions of the world.

Occurrence and distribution of Vibrio cholerae in the coastal environment of Peru

The occurrence and distribution of Vibrio cholerae in sea water and plankton along the coast of Peru were studied from October 1997 to June 2000, and included the 1997-98 El Niño event. Samples were collected at four sites in coastal waters off Peru at monthly intervals. Of 178 samples collected and tested, V. cholerae O1 was cultured from 10 (5.6%) samples, and V. cholerae O1 was detected by direct fluorescent antibody assay in 26 out of 159 samples tested (16.4%). Based on the number of cholera cases reported in Peru from 1997 to 2000, a significant correlation was observed between cholera incidence and elevated sea surface temperature (SST) along the coast of Peru (P < 0.001). From the results of this study, coastal sea water and zooplankton are concluded to be a reservoir for V. cholerae in Peru. The climate-cholera relationship observed for the 1997-98 El Niño year suggests that an early warning system for cholera risk can be established for Peru and neighbouring Latin American countries.

[Molecular study of Vibrio cholerae non-O1 isolated from zooplankton of São Marcos Bay/São Luis - MA, Brasil]

The study was developed to analyze the plasmidial DNA, research virulence genes and identify genetic diversity of 31 strains of Vibrio cholerae non-O1 isolated from zooplankton of the Bacanga and Anil rivers in São Luis-MA. The study of plasmidial DNA showed 2 or 3 plasmids from 10 strains between 5.5 and 40 kilobasis. There was only single ribotype pattern. PCR methods did not show the genes ctxA, ace and zot, while RADP-PCR identified genetic diversity in the strains, showing the potential for variability in this species.

Distribution of potentially pathogenic bacteria as free living and plankton associated in a marine coastal zone

AIMS

To determine the abundance of faecal and nonfaecal bacteria related to human and animal health, as free living or associated with small (>64 microm) and large (>200 microm) plankton, samples were collected monthly from the coastal zone at Messina (Italy).

METHODS AND RESULTS

Different enrichment and selective cultural methods were used to determine the abundance of bacteria in sea water and plankton. The bacteria were more frequently isolated from water and large plankton than from small plankton. Vibrio and Aeromonas spp. showed different distribution patterns in water and plankton. Faecal indicators were always present in water and the large size class plankton samples. Enterococci associated with large plankton were more abundant than E. coli in the winter. Vibrio species distributions were different in water and plankton samples. Among arcobacters only A. butzleri was isolated from water and plankton samples. Campylobacter spp. was always absent in small plankton and more frequent in large plankton than in water.

CONCLUSIONS

The colonization of zooplankton by potentially pathogenic bacteria is a widespread phenomenon.

SIGNIFICANCE AND IMPACT OF THE STUDY

The presence of potentially pathogenic bacteria in sea water and associated with plankton can have ecological and epidemiological implications.

[Association between Vibrio cholerae and zooplankton of estuaries of São Marcos Bay/São Luis - MA, Brazil]

This study was carried from October 1997 to October 1998 with the purpose of investigating the link between the species Vibrio cholerae and zooplankton in the estuaries of rivers Anil and Bacanga in São Luis, Maranhão. Research of viable but non culturable forms of Vibrio cholerae O1, and analyze the correlation between pH values, salinity and water temperature with the presence of bacteria in zooplankton samples. The traditional method of cultivation and fluorescent antibody technique were applied to detect the bacteria. A total of 52 samples of zooplankton were collected. There was a predominance of Copepoda. The culture enabled 55 isolates of Vibrio cholerae non-O1. The serogroups O1 and O139 were identified in 37 (71.1%) and 17 (32.7%) samples respectively by the fluorescence. Viable but non culturable forms of Vibrio cholerae were detected in 70.8% of the samples studied. A significant correlation was established between salinity and the water's pH value and Vibrio cholerae.

Are readily culturable bacteria in coastal North Sea waters suppressed by selective grazing mortality?

We studied the growth of six culturable bacterial lineages from coastal North Sea picoplankton in environmental samples under different incubation conditions. The grazing pressure of heterotrophic nanoflagellates (HNF) was reduced either by double prefiltration through 0.8- micro m-pore-size filters or by 10-fold dilutions with 0.2- micro m (pore-size) prefiltered seawater. We hypothesized that those gamma-proteobacterial genera that are rapidly enriched would also be most strongly affected by HNF regrowth. In the absence of HNF, the mean protein content per bacterial cell increased in both treatments compared to environmental samples, whereas the opposite trend was found in incubations of unaltered seawater. Significant responses to the experimental manipulations were observed in Alteromonas, Pseudoalteromonas, and Vibrio populations. No treatment-specific effects could be detected for members of the Roseobacter group, the Cytophaga latercula-C. marinoflava lineage, or the NOR5 clade. Statistical analysis confirmed a transient increase in the proportions of Alteromonas, Pseudoalteromonas, and Vibrio cells at reduced HNF densities only, followed by an overproportional decline during the phase of HNF regrowth. Cells from these genera were significantly larger than the community average in the dilution treatments, and changes in their relative abundances were negatively correlated with HNF densities. Our findings suggest that bacteria affiliated with frequently isolated genera such as Alteromonas, Pseudoalteromonas, and Vibrio might be rare in coastal North Sea picoplankton because their rapid growth response to changing environmental conditions is counterbalanced by a higher grazing mortality.

Bacteria of the gamma-subclass Proteobacteria associated with zooplankton in Chesapeake Bay

The seasonal abundance of gamma-subclass Proteobacteria, Vibrio-Photobacterium, Vibrio cholerae-Vibrio mimicus, Vibrio cincinnatiensis, and Vibrio vulnificus in the Choptank River of Chesapeake Bay associated with zooplankton was monitored from April to December 1996. Large (>202- microm) and small (64- to 202- microm) size classes of zooplankton were collected, and the bacteria associated with each of the zooplankton size classes were enumerated by fluorescent oligonucleotide direct count. Large populations of bacteria were found to be associated with both the large and small size classes of zooplankton. Also, the species of bacteria associated with the zooplankton showed seasonal abundance, with the largest numbers occurring in the early spring and again in the summer, when zooplankton total numbers were correspondingly large. Approximately 0.01 to 40.0% of the total water column bacteria were associated with zooplankton, with the percentage of the total water column bacteria population associated with zooplankton varying by season. A taxonomically diverse group of bacteria was associated with zooplankton, and a larger proportion was found in and on zooplankton during the cooler months of the year, with selected taxa comprising a larger percent of the Bacteria in the summer. V. cholerae-V. mimicus and V. vulnificus comprised the bulk of the large and small zooplankton-associated Vibrio-Photobacterium species. In contrast, V. cincinnatiensis accounted for less than 0.1 to 3%. It is concluded that water column and zooplankton bacterial populations vary independently with respect to species composition since no correlation was observed between taxa occurring with highest frequency in the water column and those in association with zooplankton.

Effects of global climate on infectious disease: the cholera model

Recently, the role of the environment and climate in disease dynamics has become a subject of increasing interest to microbiologists, clinicians, epidemiologists, and ecologists. Much of the interest has been stimulated by the growing problems of antibiotic resistance among pathogens, emergence and/or reemergence of infectious diseases worldwide, the potential of bioterrorism, and the debate concerning climate change. Cholera, caused by Vibrio cholerae, lends itself to analyses of the role of climate in infectious disease, coupled to population dynamics of pathogenic microorganisms, for several reasons. First, the disease has a historical context linking it to specific seasons and biogeographical zones. In addition, the population dynamics of V. cholerae in the environment are strongly controlled by environmental factors, such as water temperature, salinity, and the presence of copepods, which are, in turn, controlled by larger-scale climate variability. In this review, the association between plankton and V. cholerae that has been documented over the last 20 years is discussed in support of the hypothesis that cholera shares properties of a vector-borne disease. In addition, a model for environmental transmission of cholera to humans in the context of climate variability is presented. The cholera model provides a template for future research on climate-sensitive diseases, allowing definition of critical parameters and offering a means of developing more sophisticated methods for prediction of disease outbreaks.

Effect of alum on free-living and copepod-associated Vibrio cholerae O1 and O139

The effects of alum [KAl(SO4)2] on free-living and copepod-associated Vibrio cholerae O1 and O139 were investigated by using plate counts and immunofluorescence direct viable counting (DVC). Growth of alum-treated cells in 0.5/1000 Instant Ocean seawater was inhibited, i.e., no growth was obtained on Luria-Bertani (LB) agar or thiosulfate-citrate-bile salt-sucrose (TCBS) agar. However, a significant number of the inhibited cells maintained viability, as measured by DVC. In comparison, a significant number of V. cholerae organisms associated with zooplankton, most of which were crustacean copepods, were viable but nonculturable, with only a small number of cells retaining culturability on LB and TCBS agar. Both DVC and viable plate counts (CFU) were significantly greater for V. cholerae O1 and O139 associated with zooplankton than for V. cholerae in water alone, i.e., without copepods. It is concluded that alum is an effective coagulant but not an effective killing agent for V. cholerae and that association with copepods offers protection for V. cholerae O1 and O139 against alum and chlorine treatments.

Global climate and infectious disease: the cholera paradigm

The origin of cholera has been elusive, even though scientific evidence clearly shows it is a waterborne disease. However, standard bacteriological procedures for isolation of the cholera vibrio from environmental samples, including water, between epidemics generally were unsuccessful. Vibrio cholerae, a marine vibrio, requiring salt for growth, enters into a dormant, viable but nonculturable stage when conditions are unfavorable for growth and reproduction. The association of Vibrio cholerae with plankton, notably copepods, provides further evidence for the environmental origin of cholera, as well as an explanation for the sporadic and erratic occurrence of cholera epidemics. On a global scale, cholera epidemics can now be related to climate and climatic events, such as El Niño, as well as the global distribution of the plankton host. Remote sensing, with the use of satellite imagery, offers the potential for predicting conditions conducive to cholera outbreaks or epidemics.