Hans-Uwe Dahms

Inhibition of biofouling by marine microorganisms and their metabolites

Abstract Development of microbial biofilms and the recruitment of propagules on the surfaces of man-made structures in the marine environment cause serious problems for the navies and for marine industries around the world. Current antifouling technology is based on the application of toxic substances that can be harmful to the natural environment. For this reason and the global ban of tributyl tin (TBT), there is a need for the development of “environmentally-friendly” antifoulants. Marine microbes are promising potential sources of non-toxic or less-toxic antifouling compounds as they can produce substances that inhibit not only the attachment and/or growth of microorganisms but also the settlement of invertebrate larvae and macroalgal spores. However, so far only few antilarval settlement compounds have been isolated and identified from bacteria. In this review knowledge about antifouling compounds produced by marine bacteria and diatoms are summarised and evaluated and future research directions are highlighted.

Marine Biofilms as Mediators of Colonization by Marine Macroorganisms: Implications for Antifouling and Aquaculture

In the marine environment, biofilms on submerged surfaces can promote or discourage the settlement of invertebrate larvae and macroalgal spores. The settlement-mediating effects of biofilms are believed to involve a variety of biofilm attributes including surface chemistry, micro-topography, and a wide range of microbial products from small-molecule metabolites to high-molecular weight extracellular polymers. The settled organisms in turn can modify microbial species composition of biofilms and thus change the biofilm properties and dynamics. A better understanding of biofilm dynamics and chemical signals released and/or stored by biofilms will facilitate the development of antifouling and mariculture technologies. This review provides a brief account of 1) existing knowledge of marine biofilms that are relevant to settlement mediation, 2) biotechnological application of biofilms with respect to developing non-toxic antifouling technologies and improving the operation of aquaculture facilities, and 3) challenges and future directions for advancing our understanding of settlement-mediating functions of biofilms and for applying this knowledge to real-life situations.

Microalgae - A promising tool for heavy metal remediation

Biotechnology of microalgae has gained popularity due to the growing need for novel environmental technologies and the development of innovative mass-production. Inexpensive growth requirements (solar light and CO2), and, the advantage of being utilized simultaneously for multiple technologies (e.g. carbon mitigation, biofuel production, and bioremediation) make microalgae suitable candidates for several ecofriendly technologies. Microalgae have developed an extensive spectrum of mechanisms (extracellular and intracellular) to cope with heavy metal toxicity. Their wide-spread occurrence along with their ability to grow and concentrate heavy metals, ascertains their suitability in practical applications of waste-water bioremediation. Heavy metal uptake by microalgae is affirmed to be superior to the prevalent physicochemical processes employed in the removal of toxic heavy metals. In order to evaluate their potential and to fill in the loopholes, it is essential to carry out a critical assessment of the existing microalgal technologies, and realize the need for development of commercially viable technologies involving strategic multidisciplinary approaches. This review summarizes several areas of heavy metal remediation from a microalgal perspective and provides an overview of various practical avenues of this technology. It particularly details heavy metals and microalgae which have been extensively studied, and provides a schematic representation of the mechanisms of heavy metal remediation in microalgae.

Expression profiles of seven glutathione S-transferase (GST) genes in cadmium-exposed river pufferfish (Takifugu obscurus)

Glutathione S-transferase (GST; EC 2.5.1.18) plays a critical role in detoxification pathways. In this study, we report cloning and expression of seven genes of the GST family of the pufferfish Takifugu obscurus together with mRNA tissue distribution pattern and time-course of expression in response to exposure to cadmium. At basal levels of tissue expression, GST-Mu is highly expressed in liver compared with other tissues. When fish were exposed to cadmium (5 mg/L for 96 h), expression of GST-MAPEG, GST-Mu, GST-Omega, and GST-Zeta was greatly increased, whereas GST-Alpha and GST-Kappa genes showed no significant response. These findings suggest that gene expression of a number of GST isoforms in T. obscurus is modulated in response to exposure to cadmium. We propose GST-Mu, GST-Theta, and GST-Zeta as candidate biomarkers for heavy metal exposure in this fish.

The metazoan meiobenthos along a depth gradient in the Arctic Laptev Sea with special attention to nematode communities

Abstract The meiobenthos along a depth transect of oligotrophic sediments in the Arctic Laptev Sea was studied. The meiobenthos followed the general trends reported from other studies: densities decreased with depth in relation to the more limited supply of degradable organic matter at greater depths. Although the sediments along the transect were poor in organic matter in comparison with the NE Atlantic, the densities fitted well with the meiobenthic densities reported from the latter area. It is suggested that the meiobenthos in the cold polar waters is adapted to this extreme environment by a rapid response to short food pulses to the sediments. Nematodes were identified up to genus level and assigned to trophic groups. A total of 32 families comprising 95 genera were found along the transect. The communities were dominated by deposit feeders whose importance increased with depth. Both TWINSPAN and CCA analyses revealed a community shift along the depth transect: a shelf community dominated by Microlaimus and Chromadora could be distinguished from a slope community dominated by Monhystera and Leptolaimus. Generic diversity decreased with depth.

Antifouling potential of cyanobacteria: a mini-review

Abstract Cyanobacteria produce a variety of bioactive metabolites that may have allelochemical functions in the natural environment, such as in the prevention of fouling by colonising organisms. Chemical compounds from cyanobacteria are also of biotechnological interest, especially for clinical applications, because of their antibiotic, algicidal, cytotoxic, immunosupressive and enzyme inhibiting activities. Cyanobacterial metabolites have the potential for use in antifouling technology, since they show antibacterial, antialgal, antifungal and antimacrofouling properties which could be expoited in the prevention of biofouling on man-made substrata in the aquatic environment. Molecules with antifouling activity represent a number of types including fatty acids, lipopeptides, amides, alkaloids, terpenoids, lactones, pyrroles and steroids. The isolation of biogenic compounds and the determination of their structure may provide leads for future development of, for example, environmentally friendly antifouling paints. An advantage of exploring the efficacy of cyanobacterial products is that the organisms can be grown in mass culture, which can be manipulated to achieve optimal production of bioactive substances. Phycotoxins and related products from cyanobacteria may serve as materials for antimicro- and antimacrofouling applications. A survey of antibiotic compounds with antifouling potential revealed more than 21 different antifouling substances from 27 strains of cyanobacteria.

Algal photosynthetic responses to toxic metals and herbicides assessed by chlorophyll a fluorescence.

Chlorophyll a fluorescence is established as a rapid, non-intrusive technique to monitor photosynthetic performance of plants and algae, as well as to analyze their protective responses. Apart from its utility in determining the physiological status of photosynthesizers in the natural environment, chlorophyll a fluorescence-based methods are applied in ecophysiological and toxicological studies to examine the effect of environmental changes and pollutants on plants and algae (microalgae and seaweeds). Pollutants or environmental changes cause alteration of the photosynthetic capacity which could be evaluated by fluorescence kinetics. Hence, evaluating key fluorescence parameters and assessing photosynthetic performances would provide an insight regarding the probable causes of changes in photosynthetic performances. This technique quintessentially provides non-invasive determination of changes in the photosynthetic apparatus prior to the appearance of visible damage. It is reliable, economically feasible, time-saving, highly sensitive, versatile, accurate, non-invasive and portable; thereby comprising an excellent alternative for detecting pollution. The present review demonstrates the applicability of chlorophyll a fluorescence in determining photochemical responses of algae exposed to environmental toxicants (such as toxic metals and herbicides).

Isolation of bacterial metabolites as natural inducers for larval settlement in the marine polychaete Hydroides elegans (Haswell)

The bacterial component of marine biofilms plays an important role in the induction of larval settlement in the polychaete Hydroides elegans. In this study, we provide experimental evidence that bacterial metabolites comprise the chemical signal for larval settlement. Bacteria were isolated from biofilms, purified and cultured according to standard procedures. Bacterial metabolites were isolated from spent culture broth by chloroform extraction as well as by closed-loop stripping and adsorption of volatile components on surface-modified silica gel. A pronounced biological activity was exclusively observed when concentrated metabolites were adsorbed on activated charcoal. Larvae did not respond to waterborne metabolites when prevented from contacting the bacterial film surface. These results indicate that an association of the chemical signal with a sorbent-like substratum may be an essential cofactor for the expression of biological activity. The functional role of bacterial exopolymers as an adsorptive matrix for larval settlement signals is discussed.

Effect of cadmium exposure on expression of antioxidant gene transcripts in the river pufferfish, Takifugu obscurus (Tetraodontiformes).

Cadmium (Cd) is a non-essential toxic heavy metal with the potential to induce oxidative stress. Cd toxicity and its capacity for accumulation in aquatic habitats have earned its recognition as a pollutant of immediate and widespread concern. To obtain a better understanding of oxidative stress-associated gene expression in different tissues, six antioxidant genes such as catalase (CAT), glutathione reductase (GR), glutathione peroxidase 1a (GPx1a), glutathione peroxidase 1b (GPx1b), Cu/Zn superoxide dismutase (Cu/Zn-SOD), and Mn superoxide dismutase (Mn-SOD) were cloned and fully sequenced in the river pufferfish, Takifugu obscurus. On tissue specific mRNA expression, the liver showed the highest expression when compared to other tissues, even though each antioxidant gene showed different modes of expression patterns in the examined tissues. Of the various antioxidant genes, GR was the most highly expressed in the liver, followed by CAT, GPx1, and Cu/Zn-SOD. For the time-course experiment, all the antioxidant genes were significantly induced over time except for Cu/Zn-SOD in the liver, and there was a 5-fold induction in hepatic GR, CAT, and Mn-SOD mRNA compared to the control. These findings indicate that the liver of T. obscurus has a robust antioxidant system. In addition, these results suggest that Cd exposure modulates the expression of antioxidant genes, and would indicate that the antioxidant genes would be a relevant biomarker of trace metal pollution such as Cd exposure in T. obscurus.

Two-generation toxicity study on the copepod model species Tigriopus japonicus

Previous studies on the intertidal copepod Tigriopus japonicus have demonstrated that it is a suitable model species for the assessment of acute toxicities of marine pollutants. In order to standardize T. japonicus for use in environmental risk assessment involving whole life cycle exposure, we tested nine pollutants for their effects on growth and reproduction during a two-generation life cycle exposure test. Nauplii (F 0) were exposed to a range of concentrations of each chemical in a static renewal culture system. Broods of the second generation (F1) were subsequently exposed to the same concentrations for one full life cycle. Of the seven traits (nauplius phase, development time, survival, sex ratio, number of clutch, nauplii per clutch and fecundity), only the length of the nauplius phase and development time showed a greater sensitivity to chemical exposure. Between the two sensitive traits, the period of the nauplius phase was more sensitive than cohort generation time. Biocides significantly increased the maturation period of nauplii as well as copepodids in F 0 generation. In this study, it was demonstrated that T. japonicus could also be used in reproduction and life cycle tests and it provides an opportunity for testing the chronic and subchronic toxic effects of marine pollutants. Further validation and harmonization in a multi-centric study involving other laboratories of the region will strengthen its use as a supplement to existing model species.