Rocky de Nys

Quorum‐sensing cross talk: isolation and chemical characterization of cyclic dipeptides from Pseudomonas aeruginosa and other Gram‐negative bacteria

In cell‐free Pseudomonas aeruginosa culture supernatants, we identified two compounds capable of activating an N‐acylhomoserine lactone (AHL) biosensor. Mass spectrometry and NMR spectroscopy revealed that these compounds were not AHLs but the diketopiperazines (DKPs), cyclo(ΔAla‐l‐Val) and cyclo(l‐Pro‐l‐Tyr) respectively. These compounds were also found in cell‐free supernatants from Proteus mirabilis, Citrobacter freundii and Enterobacter agglomerans [cyclo(ΔAla‐l‐Val) only]. Although both DKPs were absent from Pseudomonas fluorescens and Pseudomonas alcaligenes, we isolated, from both pseudomonads, a third DKP, which was chemically characterized as cyclo(l‐Phe‐l‐Pro). Dose–response curves using a LuxR‐based AHL biosensor indicated that cyclo(ΔAla‐l‐Val), cyclo(l‐Pro‐l‐Tyr) and cyclo(l‐Phe‐l‐Pro) activate the biosensor in a concentration‐dependent manner, albeit at much higher concentrations than the natural activator N‐(3‐oxohexanoyl)‐l‐homoserine lactone (3‐oxo‐C6‐HSL). Competition studies showed that cyclo(ΔAla‐l‐Val), cyclo(l‐Pro‐l‐Tyr) and cyclo(l‐Phe‐l‐Pro) antagonize the 3‐oxo‐C6‐HSL‐mediated induction of bioluminescence, suggesting that these DKPs may compete for the same LuxR‐binding site. Similarly, DKPs were found to be capable of activating or antagonizing other LuxR‐based quorum‐sensing systems, such as the N‐butanoylhomoserine lactone‐dependent swarming motility of Serratia liquefaciens. Although the physiological role of these DKPs has yet to be established, their activity suggests the existence of cross talk among bacterial signalling systems.

Growth, Lipid Content, Productivity, and Fatty Acid Composition of Tropical Microalgae for Scale-Up Production

Biomass and lipid productivity, lipid content, and quantitative and qualitative lipid composition are critical parameters in selecting microalgal species for commercial scale‐up production. This study compares lipid content and composition, and lipid and biomass productivity during logarithmic, late logarithmic, and stationary phase of Nannochloropsis sp., Isochrysis sp., Tetraselmis sp., and Rhodomonas sp. grown in L1‐, f/2‐, and K‐medium. Of the tested species, Tetraselmis sp. exhibited a lipid productivity of 3.9–4.8 g m−2 day−1 in any media type, with comparable lipid productivity by Nannochloropsis sp. and Isochrysis sp. when grown in L1‐medium. The dry biomass productivity of Tetraselmis sp. (33.1–45.0 g m−2 day−1) exceeded that of the other species by a factor 2–10. Of the organisms studied, Tetraselmis sp. had the best dry biomass and/or lipid production profile in large‐scale cultures. The present study provides a practical benchmark, which allows comparison of microalgal production systems with different footprints, as well as terrestrial systems. Biotechnol. Bioeng. 2010;107: 245–257.

The impact and control of biofouling in marine aquaculture: a review.

Biofouling in marine aquaculture is a specific problem where both the target culture species and/or infrastructure are exposed to a diverse array of fouling organisms, with significant production impacts. In shellfish aquaculture the key impact is the direct fouling of stock causing physical damage, mechanical interference, biological competition and environmental modification, while infrastructure is also impacted. In contrast, the key impact in finfish aquaculture is the fouling of infrastructure which restricts water exchange, increases disease risk and causes deformation of cages and structures. Consequently, the economic costs associated with biofouling control are substantial. Conservative estimates are consistently between 5–10% of production costs (equivalent to US

Mini review: Biomimetic models and bioinspired surfaces for fouling control.

1.5 to 3 billion yr−1), illustrating the need for effective mitigation methods and technologies. The control of biofouling in aquaculture is achieved through the avoidance of natural recruitment, physical removal and the use of antifoulants. However, the continued rise and expansion of the aquaculture industry and the increasingly stringent legislation for biocides in food production necessitates the development of innovative antifouling strategies. These must meet environmental, societal, and economic benchmarks while effectively preventing the settlement and growth of resilient multi-species consortia of biofouling organisms.

CHEMICAL MEDIATION OF COLONIZATION OF SEAWEED SURFACES1

Nature provides many examples of mechanisms to control fouling. These defences can be copied (biomimetic) or tailored (bioinspired) to solve problems of fouling on manmade structures. With increasing research in this area over the last two decades, it is timely to review this burgeoning subject, in particular as the biofouling field shifts focus towards novel, physical mechanisms to prevent and control fouling. This change is being promoted by advances in nano- and micro-scale patterning as well as in a variety of nano-biotechnologies, which are transforming the translation of natural surfaces into experimental materials. In this article, research on the defence of marine organisms against fouling and the technologies they are defining is reviewed.

Quorum sensing antagonism from marine organisms

The surfaces of macroalgal thalli are colonized by planktonic propagules (larvae, spores, cells, etc.) from a wide diversity of eukaryotes and prokaryotes. Colonization (here defined broadly to include processes such as settlement, attachment, metamorphosis, biofilm formation, and infection) of seaweed surfaces can be both induced and inhibited by metabolites produced at those surfaces. However, detailed examples of chemically mediated interactions at seaweed surfaces for which chemical cues have been characterized, quantified in situ, a biological effect determined, and the consequences to the demography of the seaweeds or colonizers demonstrated are very rare. Here we briefly review the literature on both deterrents (“natural antifoulants”) and inducers of colonization and on interactions at seaweed surfaces between the hosts and associated bacterial biofilms. One theme that emerges is the strong need to integrate ecology, cell biology, and chemistry to understand the distribution of surface‐active molecules in situ and their ecological consequences. This multidisciplinary approach is further emphasized for research on biofilms on seaweeds, where recently developed molecular tools for characterizing bacterial communities are opening up an entire new area of marine chemical ecology. Finally, we emphasize an integrated approach to the topic, as we believe that many aspects of somewhat disparate fields including, for example, induction of larval settlement, algal pathogenesis, and the molecular biology of bacterial signaling can be usefully viewed within the overall framework of chemical mediation of surface colonization.

Chemical cues for surface colonization

With the global emergence of multiresistant bacteria there is an increasing demand for development of new treatments to combat pathogens. Bacterial cell–cell communication [quorum sensing (QS)] regulates expression of virulence factors in a number of bacterial pathogens and is a new promising target for the control of infectious bacteria. We present the results of screening of 284 extracts of marine organisms from the Great Barrier Reef, Australia, for their inhibition of QS. Of the 284 extracts, 64 (23%) were active in a general, LuxR-derived QS screen, and of these 36 (56%) were also active in a specific Pseudomonas aeruginosa QS screen. Extracts of the marine sponge Luffariella variabilis proved active in both systems. The secondary metabolites manoalide, manoalide monoacetate, and secomanoalide isolated from the sponge showed strong QS inhibition of a lasB::gfp(ASV) fusion, demonstrating the potential for further identification of specific QS antagonists from marine organisms.

Algal biochar – production and properties

Colonization of surfaces in marine benthic environments is often one of the most significant moments in the life history of benthic organisms, representing, for example, a change from a planktonic to a benthic existence, a shift from a mobile to a sessile life form, or the initiation of pathogenesis. Many of the surfaces that are colonized are, in fact, other marine organisms, and in a general sense there is widespread evidence that specific chemical cues derived from marine organisms affect colonization by both marine prokaryotes and eukaryotes. However, detailed information for any one system on the nature of such cues, their distribution in situ, and their effects on the demography of colonizers is rare. Here, we selectively review the literature on chemical cues for colonization in the sea, focussing on contrasts between positive (inducers) and negative (inhibitors, deterrents) cues and on prokaryote/eukaryote interactions. We also consider whether generalized life history or natural history characteristics of colonizers (i.e., the mobility of a propagule, the extent to which a species is a habitat generalist or specialist, etc.) affect their response to chemical cues, and we touch briefly on some recent highlights relevant to the critical interplay between hydrodynamics and chemistry. A number of important methodological concerns are now being addressed through the introduction of field assays and analyses for chemical cues, and through molecular techniques for the characterization of microbial biofilms. These developments are encouraging, as is the increasingly multidisciplinary and cross-taxonomic approach to research in this area.

Larval settlement of the common Australian sea urchin Heliocidaris erythrogramma in response to bacteria from the surface of coralline algae

This study presents baseline data on the physiochemical properties and potential uses of macroalgal (seaweed) biochar produced by pyrolysis of eight species of green tide algae sourced from fresh, brackish and marine environments. All of the biochars produced are comparatively low in carbon content, surface area and cation exchange capacity, but high in pH, ash, nitrogen and extractable inorganic nutrients including P, K, Ca and Mg. The biochars are more similar in characteristics to those produced from poultry litter relative to those derived from ligno-cellulosic feedstocks. This means that, like poultry litter biochar, macroalgal biochar has properties that provide direct nutrient benefits to soils and thereby to crop productivity, and will be particularly useful for application on acidic soils. However, macroalgal biochars are volumetrically less able to provide the carbon sequestration benefits of the high carbon ligno-cellulosic biochars.

Microtopography and antifouling properties of the shell surface of the bivalve molluscs mytilus galloprovincialis and pinctada imbricata

Bacterial biofilms are increasingly seen as important for the successful settlement of marine invertebrate larvae. Here we tested the effects of biofilms on settlement of the sea urchin Heliocidaris erythrogramma. Larvae settled on many surfaces including various algal species, rocks, sand and shells. Settlement was reduced by autoclaving rocks and algae, and by treatment of algae with antibiotics. These results, and molecular and culture-based analyses, suggested that the bacterial community on plants was important for settlement. To test this, approximately 250 strains of bacteria were isolated from coralline algae, and larvae were exposed to single-strain biofilms. Many induced rates of settlement comparable to coralline algae. The genus Pseudoalteromonas dominated these highly inductive strains, with representatives from Vibrio, Shewanella, Photobacterium and Pseudomonas also responsible for a high settlement response. The settlement response to different bacteria was species specific, as low inducers were also dominated by species in the genera Pseudoalteromonas and Vibrio. We also, for the first time, assessed settlement of larvae in response to characterised, monospecific biofilms in the field. Larvae metamorphosed in higher numbers on an inducing biofilm, Pseudoalteromonas luteoviolacea, than on either a low-inducing biofilm, Pseudoalteromonas rubra, or an unfilmed control. We conclude that the bacterial community on the surface of coralline algae is important as a settlement cue for H. erythrogramma larvae. This study is also an example of the emerging integration of molecular microbiology and more traditional marine eukaryote ecology.