With growing environmental pressures placed on our marine habitats there is concern that the prevalence and severity of diseases affecting marine organisms will increase. Yet relative to terrestrial ...systems, we know little about the underlying causes of many of these diseases. Moreover, factors such as saprophytic colonizers and a lack of baseline data on healthy individuals make it difficult to accurately assess the role of specific microbial pathogens in disease states. Emerging evidence in the field of medicine suggests that a growing number of human diseases result from a microbiome imbalance (or dysbiosis), questioning the traditional view of a singular pathogenic agent. Here we discuss the possibility that many diseases seen in marine systems are, similarly, the result of microbial dysbiosis and the rise of opportunistic or polymicrobial infections. Thus, understanding and managing disease in the future will require us to also rethink definitions of disease and pathogenesis for marine systems. We suggest that a targeted, multidisciplinary approach that addresses the questions of microbial symbiosis in both healthy and diseased states, and at that the level of the holobiont, will be key to progress in this area.
Abstract
Seaweeds (macroalgae) form a diverse and ubiquitous group of photosynthetic organisms that play an essential role in aquatic ecosystems. These ecosystem engineers contribute significantly to ...global primary production and are the major habitat formers on rocky shores in temperate waters, providing food and shelter for aquatic life. Like other eukaryotic organisms, macroalgae harbor a rich diversity of associated microorganisms with functions related to host health and defense. In particular, epiphytic bacterial communities have been reported as essential for normal morphological development of the algal host, and bacteria with antifouling properties are thought to protect chemically undefended macroalgae from detrimental, secondary colonization by other microscopic and macroscopic epibiota. This tight relationship suggests that macroalgae and epiphytic bacteria interact as a unified functional entity or holobiont, analogous to the previously suggested relationship in corals. Moreover, given that the impact of diseases in marine ecosystems is apparently increasing, understanding the role of bacteria as saprophytes and pathogens in seaweed communities may have important implications for marine management strategies. This review reports on the recent advances in the understanding of macroalgal–bacterial interactions with reference to the diversity and functional role of epiphytic bacteria in maintaining algal health, highlighting the holobiont concept.
This review discusses the diversity and ecology of seaweed (macroalgae)-associated bacteria with an emphasis on the factors that influence epiphytic community composition and function.
Nile tilapia, Oreochromis niloticus is the third most commonly farmed finfish species in the world, accounting for nearly 5% of global aquaculture production. In the past few decades much of the ...success of this species has been attributed to the development and distribution of Genetically Improved Farmed Tilapia (GIFT). Despite the increasing availability of GIFT, the productivity of small-scale farming remains highly variable, particularly in developing nations. Commercial fish-feed pellets can increase fish farm productivity; however, many small-scale farmers rely on other means of feeding fish due to the high cost and limited availability of commercial fish feed pellets. Therefore, understanding how locally-sourced feeds affect the production of GIFT is an important step towards improving feeding practices, particularly for farmers with low financial capital. This study used stable isotope analysis (SIA) and 16S rRNA gene sequencing to compare the effects of a locally-sourced vegetable-based diet and commercial pellet-based diets on the relative condition, nutrient assimilation patterns and gastrointestinal microbiota of GIFT. GIFT fed a locally-sourced diet were smaller, and in a significantly poorer condition than those fed with commercial fish feeds. SIA showed no differences in dietary carbon between the two diets; however, δ13C, poor fish condition and the abundance of specific bacterial taxa (of such as Fusobacteria) were correlated. SIA revealed that GIFT fed locally-sourced diets that predominantly consisted of vegetables were significantly enriched in δ15N despite a perceived lack of dietary protein. This enrichment suggests that GIFT fed a locally-sourced diet may be supplementing their diet via cannibalism, a behaviour representative of poor farming practice. Overall this study highlights the need to increase the availability of suitable GIFT feeds in developing nations. The development a low-cost feed alternative could improve the success of small-scale GIFT farmers in PNG, increasing both food and income security within the region.
Disease in the marine environment is predicted to increase with anthropogenic stressors and already affects major habitat-formers, such as corals and seaweeds. Solutions to address this issue are ...urgently needed. The seaweed Delisea pulchra is prone to a bleaching disease, which is caused by opportunistic pathogens and involves bacterial dysbiosis. Bacteria that can inhibit these pathogens and/or counteract dysbiosis are therefore hypothesised to reduce disease. This study aimed to identify such disease-protective bacteria and investigate their protective action. One strain, Phaeobacter sp. BS52, isolated from healthy D. pulchra, was antagonistic towards bleaching pathogens and significantly increased the proportion of healthy individuals when applied before the pathogen challenge (pathogen-only vs. BS52 + pathogen: 41-80%), and to a level similar to the control. However, no significant negative correlations between the relative abundances of pathogens and BS52 on D. pulchra were detected. Instead, inoculation of BS52 mitigated pathogen-induced changes in the epibacterial community. These observations suggest that the protective activity of BS52 was due to its ability to prevent dysbiosis, rather than direct pathogen inhibition. This study demonstrates the feasibility of manipulating bacterial communities in seaweeds to reduce disease and that mitigation of dysbiosis can have positive health outcomes.
Cyanobacteria are among the first microorganisms to have inhabited the Earth. Throughout the last few billion years, they have played a major role in shaping the Earth as the planet we live in, and ...they continue to play a significant role in our everyday lives. Besides being an essential source of atmospheric oxygen, marine cyanobacteria are prolific secondary metabolite producers, often despite the exceptionally small genomes. Secondary metabolites produced by these organisms are diverse and complex; these include compounds, such as pigments and fluorescent dyes, as well as biologically-active compounds with a particular interest for the pharmaceutical industry. Cyanobacteria are currently regarded as an important source of nutrients and biofuels and form an integral part of novel innovative energy-efficient designs. Being autotrophic organisms, cyanobacteria are well suited for large-scale biotechnological applications due to the low requirements for organic nutrients. Recent advances in molecular biology techniques have considerably enhanced the potential for industries to optimize the production of cyanobacteria secondary metabolites with desired functions. This manuscript reviews the environmental role of marine cyanobacteria with a particular focus on their secondary metabolites and discusses current and future developments in both the production of desired cyanobacterial metabolites and their potential uses in future innovative projects.
While the oceans cover more than 70% of the Earth's surface, marine derived microbial natural products have been largely unexplored. The marine environment is a habitat for many unique ...microorganisms, which produce biologically active compounds ("bioactives") to adapt to particular environmental conditions. For example, marine surface associated microorganisms have proven to be a rich source for novel bioactives because of the necessity to evolve allelochemicals capable of protecting the producer from the fierce competition that exists between microorganisms on the surfaces of marine eukaryotes. Chemically driven interactions are also important for the establishment of cross-relationships between microbes and their eukaryotic hosts, in which organisms producing antimicrobial compounds ("antimicrobials"), may protect the host surface against over colonisation in return for a nutrient rich environment. As is the case for bioactive discovery in general, progress in the detection and characterization of marine microbial bioactives has been limited by a number of obstacles, such as unsuitable culture conditions, laborious purification processes, and a lack of de-replication. However many of these limitations are now being overcome due to improved microbial cultivation techniques, microbial (meta-) genomic analysis and novel sensitive analytical tools for structural elucidation. Here we discuss how these technical advances, together with a better understanding of microbial and chemical ecology, will inevitably translate into an increase in the discovery and development of novel drugs from marine microbial sources in the future.
Healthy marine ecosystems are paramount for Earth's biodiversity and are key to sustaining the global economy and human health. The effects of anthropogenic activity represent a pervasive threat to ...the productivity of marine ecosystems, with intensifying environmental stressors such as climate change and pollution driving the occurrence and severity of microbial diseases that can devastate marine ecosystems and jeopardise food security. Despite the potentially catastrophic outcomes of marine diseases, our understanding of host‐pathogen interactions remains an understudied aspect of both microbiology and environmental research, especially when compared to the depth of information available for human and agricultural systems. Here, we identify three avenues of research in which we can advance our understanding of marine disease in the context of global change, and make positive steps towards safeguarding marine communities for future generations.
Despite the potentially catastrophic outcomes of marine diseases, our understanding of host‐pathogen interactions remains an understudied aspect of both microbiology and environmental research, especially when compared to the depth of information available for human and agricultural systems. Here, we identify three avenues of research in which we can advance our understanding marine disease in the context of global change and make positive steps towards safeguarding marine communities for future generations.
Disease outbreaks cause severe economic losses in commercially cultivated
Saccharina japonica
. Epiphytic bacteria are increasingly recognized to play an important role in
S. japonica
health and may ...also become opportunistic pathogens when the environment deteriorates. However, there is little knowledge about the epiphytic bacterial communities associated with commercially cultivated
S. japonica
and how these communities change over the harvest season. We analyzed the diversity, composition, and temporal dynamics of epiphytic bacterial communities associated with both healthy and diseased tissue of
S. japonica
over a harvest season (from April to June, 2015) at Ailian Bay, Rongcheng, China. Our results showed that Proteobacteria and Bacteroidetes were the main phyla and
Halomonas
spp. were the most dominant bacterial species. Halomonadaceae, Hyphomonadaceae, Rhodobacteraceae, and Phyllobacteriaceae families were abundant in both healthy and diseased
S. japonica
, but the relative abundance of these bacteria differed between healthy and diseased groups. Spatial (site 1, site 2, and site 3 in April) and temporal comparisons (site 3 from April to June) revealed that the bacterial community associated with cultivated
S. japonica
was influenced by sampling time and sampling site independent of the health status. Several OTUs from the Roseobacter group, including members of the genera
Sulfitobacter
and
Loktanella
, were enriched in diseased tissues suggesting these taxa could be candidate opportunistic pathogens. In contrast, OTUs belonging to the genera
Halomonas
were enriched in healthy tissues, indicating a potential beneficial role for group during the cultivation of
S. japonica
. Our results provide important baseline knowledge of the epiphytic bacterial communities and possibly pathogenic bacteria associated with commercially cultivated
S. japonica
.
Marine sessile eukaryotic hosts provide a unique surface for microbial colonisation. Chemically mediated interactions between the host and colonising microorganisms, interactions between ...microorganisms in the biofilm community and surface-specific physical and chemical conditions impact differently on the diversity and function of surface-associated microbial assemblages compared with those in planktonic systems. Understanding the diversity and ecology of surface-associated microbial communities will greatly contribute to the discovery of next-generation, bioactive compounds. On the basis of recent conceptual and technological advances insights into the microbiology of marine living surfaces are improving and novel bioactives, including those previously ascribed as host derived, are now revealed to be produced by members of the surface-associated microbial community.
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