Exploring novel bioactive compounds from marine microbes

The historical paradigm of the deep ocean as a biological 'desert' has shifted to one of a 'rainforest' owing to the isolation of many novel microbes and their associated bioactive compounds. Recently, there has been an explosion of information about novel bioactive compounds that have been isolated from marine microbes in an effort to further explore the relatively untapped marine microbes and their secondary metabolites for drug discovery. The microbes are recovered and purified from the ocean by both conventional and innovative isolation methods to obtain those previously thought to be 'uncultivable'. To overcome the difficulties and limitations associated with cultivation techniques, several DNA-based molecular methods have been developed to bypass the culture-dependent bottleneck. Bioactive compounds isolated using the above strategies have not only shown importance in biotechnological and pharmaceutical applications but have also increased our understanding of the diversity of marine microbiota, ecosystem functions and the exploitable biology.     

Marine microorganisms as biocontrol agents against fungal phytopathogens and mycotoxins

Mycotoxins are a serious food safety concern for human and animal health. Much attention should be paid to the dietary exposure to mycotoxins in order to minimise the risk of mycotoxin contamination in the food chain. Among the reported strategies to manage the mycotoxin contamination into food and feed, biological control seems a promising approach, depending on their biological origins, and on the use of living organisms or their derivatives. Marine microorganisms have developed unique metabolic and physiological capabilities to thrive in extreme habitats and produce novel metabolites which are not often present in microbes of terrestrial origin. Some marine bacteria and fungi have a good potential for the control of fungal phytopathogens and mycotoxins. Biologists and chemists are needed to work together to explore the storehouse of marine microorganisms and marine active metabolites, because marine bacteria and fungi have a huge potential for practical application in biocontrol of fungal phytopathogens and preventing mycotoxin contamination.     

Genome analysis of marine photosynthetic microbes and their global role

Four recently completed genome projects on marine Cyanobacteria have started the age of comparative genomics for marine microbes. Cyanobacteria are a group of photoautotrophic bacteria that have traditionally been under-represented in studies of complete genome sequences, as have microbes from the marine environment in general. The new genome information is of crucial importance to understanding their role in oceanic primary production, global carbon cycling and functioning of the biosphere. Marine microbes are a still almost untapped resource for the identification of novel beneficial metabolites and activities. The availability of an increasing number of genome sequences will eventually lead to a sustained development of marine biotechnology.     

Natural products as leads to antitumor drugs

The discussion in this short review emphasizes that the main and future source of novel natural products as leads to antitumor agents is probably in the areas of biology that cannot be seen, i.e. the microbial world. The review discusses the role of microbes in the production of secondary metabolites that were initially thought to be from marine invertebrates and goes on to discuss the potential for a number of well-known anticancer agents isolated from plant sources to actually be the products of a microbe-plant interaction and finishes with a discussion of the potential of microbial “cryptic clusters” as sources of novel agents/leads to anti-tumor treatments.     

Zebrafish Embryo Toxicity Microscale Model for Ichthyotoxicity Evaluation of Marine Natural Products

Marine organisms often protect themselves against their predators by chemical defensive strategy. The second metabolites isolated from marine organisms and their symbiotic microbes have been proven to play a vital role in marine chemical ecology, such as ichthyotoxicity, allelopathy, and antifouling. It is well known that the microscale models for marine chemoecology assessment are urgently needed for trace quantity of marine natural products. Zebrafish model has been widely used as a microscale model in the fields of environment ecological evaluation and drug safety evaluation, but seldom reported for marine chemoecology assessment. In this work, zebrafish embryo toxicity microscale model was established for ichthyotoxicity evaluation of marine natural products by using 24-well microplate based on zebrafish embryo. Ichthyotoxicity was evaluated by observation of multiple toxicological endpoints, including coagulation egg, death, abnormal heartbeat, no spontaneous movement, delayed hatch, and malformation of the different organs during zebrafish embryogenesis periods at 24, 48, and 72 h post-fertilization (hpf). 3,4-Dichloroaniline was used as the positive control for method validation. Subsequently, the established model was applied to test the ichthyotoxic activity of the compounds isolated from corals and their symbiotic microbes and to isolate the bioactive secondary metabolites from the gorgonian Subergorgia mollis under bioassay guidance. It was suggested that zebrafish embryo toxicity microscale model is suitable for bioassay-guided isolation and preliminary bioactivity screening of marine natural products.     

Marine chemical ecology: what''s known and what''s next?

In this review, I summarize recent developments in marine chemical ecology and suggest additional studies that should be especially productive. Direct tests in both the field and laboratory show that secondary metabolites commonly function as defenses against consumers. However, some metabolites also diminish fouling, inhibit competitors or microbial pathogens, and serve as gamete attractants; these alternative functions are less thoroughly investigated. We know little about how consumers perceive secondary metabolites or how ecologically realistic doses of defensive metabolites affect consumer physiology or fitness, as opposed to feeding behavior. Secondary metabolites have direct consequences, but they do not act in isolation from other prey characteristics or from the physical and biological environment in which organisms interact with their natural enemies. This mandates that marine chemical ecology be better integrated into a broader and more complex framework that includes aspects of physiological, population, community, and even ecosystem ecology. Recent advances in this area involve assessing how chemically mediated interactions are affected by physical factors such as flow, desiccation, UV radiation, and nutrient availability, or by biological forces such as the palatability or defenses of neighbors, fouling organisms, or microbial symbionts. Chemical defenses can vary dramatically among geographic regions, habitats, individuals within a local habitat, and within different portions of the same individual. Factors affecting this variance are poorly known, but include physical stresses and induction due to previous attack. Studies are needed to assess which consumers induce prey defenses, how responses vary in environments with differing physical characteristics, and whether the ‘induced’ responses are a direct response to consumer attack or are a defense against microbial pathogens invading via feeding wounds. Although relatively unstudied, ontogenetic shifts in concentrations and types of defenses occur in marine species, and patterns of larval chemical defenses appear to provide insights into the evolution of complex life cycles and of differing modes of development among marine invertebrates. The chemical ecology of marine microbes is vastly underappreciated even though microbes produce metabolites that can have devastating indirect effects on non-target organisms (e.g., red tide related fish kills) and significantly affect entire ecosystems. The natural functions of these metabolites are poorly understood, but they appear to deter both consumers and other microbes. Additionally, marine macro-organisms use metabolites from microbial symbionts to deter consumers, subdue prey, and defend their embryos from pathogens. Microbial chemical ecology offers unlimited possibilities for investigators that develop rigorous and more ecologically relevant approaches.     

中国北部湾光裸方格星虫可培养微生物的分离鉴定及其活性代谢物产生菌筛选

【目的】本研究从北部湾海域光裸方格星虫(Sipunculus nudus)肠道中分离鉴定可培养微生物,并对筛选菌株的代谢物活性进行研究,为后续开发和利用光裸方格星虫肠道微生物代谢产物提供理论支持。【方法】通过微生物培养、菌株分离纯化和16S rRNA基因序列分析,分析鉴定湛江、北海、防城港三地光裸方格星虫肠道可培养微生物;采用透明圈法、可见分光光度法、平板打孔法等对产胞外活性代谢物的菌株进行筛选和活性分析。【结果】中国北部湾不同海域光裸方格星虫肠道可培养微生物包括弧菌属(Vibrio)、希瓦氏菌属(Shewanella)、假交替单胞菌属(Pseudoalteromonas)、发光杆菌属(Photobacterium)和芽孢杆菌属(Bacillus)等12个细菌属。弧菌属(Vibrio)是3个地区样本共有的优势菌群。具有产胞外水解蛋白酶、壳聚糖酶、多糖以及抑菌活性等能力的菌株主要来自假交替单胞菌属(Pseudoalteromonas)、发光杆菌属(Photobacterium)和芽孢杆菌属(Bacillus)。【结论】中国北部湾不同海域光裸方格星虫肠道可培养微生物在属的种类上存在显著性差异,且光裸方格星虫肠道菌株具有产生多种胞外活性代谢物的能力,是一种良好的海洋活性代谢物来源。     

Discovery of novel metabolites from marine actinomycetes

Recent findings from culture-dependent and culture-independent methods have demonstrated that indigenous marine actinomycetes exist in the oceans and are widely distributed in different marine ecosystems. There is tremendous diversity and novelty among the marine actinomycetes present in marine environments. Progress has been made to isolate novel actinomycetes from samples collected at different marine environments and habitats. These marine actinomycetes produce different types of new secondary metabolites. Many of these metabolites possess biological activities and have the potential to be developed as therapeutic agents. Marine actinomycetes are a prolific but underexploited source for the discovery of novel secondary metabolites.     

Complex Marine Natural Products as Potential Epigenetic and Production Regulators of Antibiotics from a Marine Pseudomonas aeruginosa

Marine microbes are capable of producing secondary metabolites for defense and competition. Factors exerting an impact on secondary metabolite production of microbial communities included bioactive natural products and co-culturing. These external influences may have practical applications such as increased yields or the generation of new metabolites from otherwise silent genes in addition to reducing or limiting the production of undesirable metabolites. In this paper, we discuss the metabolic profiles of a marine Pseudomonas aeruginosa in the presence of a number of potential chemical epigenetic regulators, adjusting carbon sources and co-culturing with other microbes to induce a competitive response. As a result of these stressors certain groups of antibiotics or antimalarial agents were increased most notably when treating P. aeruginosa with sceptrin and co-culturing with another Pseudomonas sp. An interesting cross-talking event between these two Pseudomonas species when cultured together and exposed to sceptrin was observed.     

Diversity and biotechnological potential of the sponge-associated microbial consortia

Sponges are well known to harbor diverse microbes and represent a significant source of bioactive natural compounds derived from the marine environment. Recent studies of the microbial communities of marine sponges have uncovered previously undescribed species and an array of new chemical compounds. In contrast to natural compounds, studies on enzymes with biotechnological potential from microbes associated with sponges are rare although enzymes with novel activities that have potential medical and biotechnological applications have been identified from sponges and microbes associated with sponges. Both bacteria and fungi have been isolated from a wide range of marine sponge, but the diversity and symbiotic relationship of bacteria has been studied to a greater extent than that of fungi isolated from sponges. Molecular methods (e.g., rDNA, DGGE, and FISH) have revealed a great diversity of the unculturable bacteria and archaea. Metagenomic approaches have identified interesting metabolic pathways responsible for the production of natural compounds and may provide a new avenue to explore the microbial diversity and biotechnological potential of marine sponges. In addition, other eukaryotic organisms such as diatoms and unicellular algae from marine sponges are also being described using these molecular techniques. Many natural compounds derived from sponges are suspected to be of bacterial origin, but only a few studies have provided convincing evidence for symbiotic producers in sponges. Microbes in sponges exist in different associations with sponges including the true symbiosis. Fungi derived from marine sponges represent the single most prolific source of diverse bioactive marine fungal compounds found to date. There is a developing interest in determining the true diversity of fungi present in marine sponges and the nature of the association. Molecular methods will allow scientists to more accurately identify fungal species and determine actual diversity of sponge-associated fungi. This is especially important as greater cooperation between bacteriologists, mycologists, natural product chemists, and bioengineers is needed to provide a well-coordinated effort in studying the diversity, ecology, physiology, and association between bacteria, fungi, and other organisms present in marine sponges.     

海洋沉积物来源链霉菌属次生代谢产物及其生物活性研究进展

海洋沉积物是营养较为丰富的微生物栖息地,近年来从海洋沉积物中分离培养出了大量海洋链霉菌,从中还发现了一些新的属种。人们已从海洋沉积物来源链霉菌属中发现了许多具有药用价值的活性化合物,有力推动了海洋天然产物化学的发展,并为新药研发提供基础。本文就海洋沉积物来源链霉菌属次生代谢产物的结构类型及其生物活性进行简要综述。     

Observing the invisible through imaging mass spectrometry, a window into the metabolic exchange patterns of microbes

Many microbes can be cultured as single-species communities. Often, these colonies are controlled and maintained via the secretion of metabolites. Such metabolites have been an invaluable resource for the discovery of therapeutics (e.g. penicillin, taxol, rapamycin, epothilone). In this article, written for a special issue on imaging mass spectrometry, we show that MALDI-imaging mass spectrometry can be adapted to observe, in a spatial manner, the metabolic exchange patterns of a diverse array of microbes, including thermophilic and mesophilic fungi, cyanobacteria, marine and terrestrial actinobacteria, and pathogenic bacteria. Dependent on media conditions, on average and based on manual analysis, we observed 11.3 molecules associated with each microbial IMS experiment, which was split nearly 50:50 between secreted and colony-associated molecules. The spatial distributions of these metabolic exchange factors are related to the biological and ecological functions of the organisms. This work establishes that MALDI-based IMS can be used as a general tool to study a diverse array of microbes. Furthermore the article forwards the notion of the IMS platform as a window to discover previously unreported molecules by monitoring the metabolic exchange patterns of organisms when grown on agar substrates.     

Symbiotic and dietary marine microalgae as a source of bioactive molecules–experience from natural products research

Cyanobacterial metabolites have proven to be invaluable as tools in thedissection of signal transduction pathways in mammalian cells and some arecurrently under clinical evaluation as drug candidates. It is now also realizedthat cyanobacteria are the true biosynthetic origin of many bioactive moleculesisolated from marine invertebrates; marine invertebrates may sequestercyanobacteria through diet or by symbiosis. This review discusses thedietary-derived cyanobacterial origin of the dolastatins, potent cytotoxiccompounds, originally isolated from the Indian Ocean sea hare,Dolabella auricularia. A discussion on the dietarydissemination of cyanobacterial metabolites through the marine food chain isalso presented. Reference to the metabolites isolated fromDysidea sponges is given to illustrate their origin fromsymbiotic cyanobacteria associated with this organism.     

混合发酵提高2株海洋微生物菌株抑菌活性的研究

2株抑菌范围不同的海洋微生物菌株,在单独培养条件优化基础上进行混合发酵,并对混合发酵条件进行了优化测试,混合发酵结果有效的提高了菌株产生代谢产物的抑菌活性,最小抑菌浓度由单独发酵的156μL/mL、125μL/mL,单独发酵后混合的250μL/mL、218μL/mL降至32μL/mL、28μL/mL,即代谢产物抑菌活性比单独发酵提高200%,比单独发酵后混合提高300%,2株菌株混合发酵的协同效应大于单独发酵混合后的累加效应,对靶标真菌的致畸作用明显。     

Filamentous tropical marine cyanobacteria: a rich source of natural products for anticancer drug discovery

A plethora of structurally novel bioactive secondary metabolites have been reported from the prokaryotic filamentous marine cyanobacteria in the past few decades. In addition to the production of harmful toxins, these marine blue-green algae are emerging as an important source of anticancer drugs. The majority of these potent biomolecules, including the dolastatins, curacin A, hectochlorin, the apratoxins, and the lyngbyabellins, belongs to the mixed polyketide–polypeptide structural class. Furthermore, a high proportion of these natural products target eukaryotic cytoskeleton, such as tubulin and actin microfilaments, making them an attractive source of potential anticancer drugs. In recent years, a number of potent marine cyanobacteria have also been reported to modulate cell death and apoptosis in cancer cells as well as target enzymes such as histone deacetylase. A number of marine cyanobacterial compounds have also served as structural templates for the generation of new drug leads, further attesting to the importance of these marine microbes as an important source of new pharmaceuticals. This review serves to highlight the chemistry and biology of selected anticancer marine cyanobacterial natural products exhibiting significant biological activities in the nanomolar or submicromolar range, and their discussion will be based on the different modes of action.     

Trench connection

'Trench Connection' was the first international symposium focusing primarily on the hadal zone (depths greater than 6000 m). It was held at the University of Tokyo's Atmosphere and Ocean Research Institute in November 2010. The symposium was successful in having attracted an international collective of scientists and engineers to discuss the latest developments in the exploration and understanding of the deepest environments on Earth. The symposium sessions were categorized into three themes: (i) new deep-submergence technology; (ii) trench ecology and evolution; and (iii) the physical environment. Recent technological developments have overcome the challenges of accessing the extreme depths, which have in turn prompted an international renewed interest in researching physical and biological aspects of the hadal ecosystems. This bringing together of international participants from different disciplines led to healthy discussions throughout the symposium, providing potential opportunities and realizations of where the future of unravelling hadal ecology lies. Hadal science is still at relatively rudimentary levels compared with those of shallower marine environments; however, it became apparent at the symposium that it is now an ever-expanding scientific field.     

石磺海牛共附生细菌的分离和活性菌株筛选

[目的]研究深圳大鹏半岛海域石磺海牛中可培养的共附生细菌的数量和种类,并对分离获得菌株的代谢产物进行活性筛选.[方法]通过R2A平板培养、分离纯化和16S rRNA测序,分析鉴定石磺海牛中5个部位可培养细菌;使用分离菌株的菌液及发酵液上清,测定对群体感应信号分子降解的活性和抗生物膜活性.[结果]从石磺海牛中共分离到21...     

海洋环境中难培养微生物的寡营养培养

海洋中存在着丰富的微生物资源, 但迄今为止能够在实验室培养的微生物却不到1%, 而且能够通过培养得到的环境优势种更少, 这成为当代环境微生物学研究和海洋资源开发的最大障碍。过去十多年来, 通过不断改进培养方法和检测手段, 发明了许多新颖独特的技术, 提高了培养效率。特别是通过海洋微生物的寡营养培养技术, 分离并命名了一些难培养微生物, 给予人们极大的启发。海洋微生物资源的可持续性开发和利用, 是21世纪人类发展的重要方向, 是我们研究海洋微观世界的基础, 值得微生物学界同仁的共同关注。     

Actinophages as indicators of actinomycete taxa in marine environments

It is necessary to continue to screen for new metabolites and evaluate the potential of less known and new bacterial taxa so that new and improved compounds for future use against drug-resistant bacteria or for chemical modification may be developed. There has been considerable interest in the detection and identification of marine microorganisms since they have been reported to produce bioactive compounds ranging from antitumour to antibacterial and antiviral agents. In this study, an improved technique that involves the exploitation of marine actinophages as indicators of the marine actinomycete taxa and uses marine bacteriophages as tools to reduce the numbers of common marine bacteria, which impedes the growth of rare actinomycetes on isolation plates, has been applied. This technique reduced the numbers of colony forming units of unwanted bacteria on isolation plates and hence increased the chances of detecting novel marine actinomycete genera for isolation and subsequent screening for antiviral activity.     

Bioprocess Intensification for Production of Novel Marine Bacterial Antibiotics Through Bioreactor Operation and Design

There is a lack of research into bioreactor engineering and fermentation protocol design in the field of marine bacterial antibiotic production. Most production strategies are carried out at the shake-flask level and lack a mechanistic understanding of the antibiotic production process, offering poor prospects for successful scale-up. This review shows that data need to be collated on media and physical optima differences between the trophophase and idiophase, along with investigations into the control mechanisms for biosynthesis, to allow implementation of novel fermentation protocols. Immobilization may play a part in bioprocess intensification of marine bacterial antibiotic production, through again this area is understudied. Similarly, mass transfer and shear stress data of fermentations are needed to provide the bioreactor design requirements to intensify antibiotic biosynthesis, with process scale-up in mind. The application of bioprocess intensification methods to the production of antibiotics (and other metabolites) from marine microbes will become an important strategy for improving supply of natural products, in order to assess their suitability as chemotherapeutic drugs. Received March 11, 1999; accepted May 4, 1999.