The oceans are massively complex and consist of diverse assemblages of life forms. The water column of the oceans contains approximately 106 bacterial cells per ml[56]. Marine bacteria and other marine microorganisms develop unique metabolic and physiological capabilities. These capabilities enable them to survive in extreme habitats and to produce compounds that might not be produced by their terrestrial counterparts. Since 1990, the number of bioactive metabolites from marine bacteria has exponentially increased (Figure 3)[10,28, 30,57-59].
0 100 200 300 400 500 600 700 800
Number of Metabolites
1966 1970 1975 1980 1985 1990 1995 2000 2004 2008 Year
Figure 3: Annual increase in the number of marine bacterial metabolites, accord-ing to Laatsch[60] and AntiBase[61].
Biological activity, a second point of comparison, is classified into eight areas.
They are anticancer, antibiotic (including antibacterial, antifungal and antimalarial), anti-inflammatory, antiviral, immunomodulatory, agricultural, methodology and other. Figure 4 shows the types of testings carried out up to 2005, suggestive that the
“catchall” category of methodology was increasing. Testing for anticancer activity remains one of the least used assays. Increasingly results are appearing in the litera-ture for antimalarial, antitubercular and antiinfective assays against drug-resistant microorganisms. There can be no doubt that there is an urgent need for new thera-peutics in those areas, but also in agricultural areas where resistance to the standard anthelmintics is becoming a serious problem[59].
The search for new bioactive chemicals from marine organisms resulted in the isolation of about 10000 metabolites [62], many of which are potential biomedicals.
These agents show a broad spectrum of biological activities. Up to now, bioactive agents were isolated extensively from Streptomyces, Alteromonas/Pseudoalteromo-nas, Bacillus, Vibrio, PseudomoAlteromonas/Pseudoalteromo-nas, and Cytophaga (Figure 5). These microorgan-isms were isolated from seawater, sediments, algae and marine invertebrates. They are able to produce quinones, polyenes, macrolides, alkaloids, peptides and to a lesser extent terpenoids.
20%
1% 41%
3%
6%
5%
3%
21% Antibiotic
Anticancer
Immunomodulatory Antiinflammatory Agricultural Antiviral Other
Methodology
Figure 4: Reported distribution of biological testing carried out on marine natural product extracts and isolated compounds to 2004.
241
4725 37 29 25 19 15 1 14 9 2 7 19 7 2 17 6 1 6 2 1 1 65
0 50 100 150 200 250 300
Streptom yces
Pseudoalteromonas Vibrio
Micromonospora Cyclobacterium
Janibacter Marinobacter
Salinospora Myxobacteria
Flexibacter Pelagiobacter
Photobacterium
Number of Metabolites
Figure 5: Number of secondary metabolites isolated from some marine bacteria according to their taxonomic origin since 1966 till 2004[60].
The pioneering work of Okami and co-workers represents the first building unit in the knowledge of the chemistry of marine derived bacteria, in particular of Actin-omycetes. They have reported the isolation of a benzanthraquinone antibiotics SS-228Y (34) and SS-228R (35) from the actinomycete Chainia purpurogena[63]. On othe ther hand, they isolated istamycins A (36) and B (37) antibiotics from Strepto-myces tenjimariensis. Isatin; 3,2-indolinedione (32), as one of the early marine me-tabolites, was produced by a bacterium colonizing the surface of the embryos of the
shrimp Palaemon macrodactylus. It is responsible for the protection of eggs against the pathogen fungus Lagenidium callinectes[64]. Macrolactin A (33), a new mac-rolide, having antibacterial, antiviral and cytotoxic activities, was isolated from an unidentified unicellular deep sea bacterium[65].
HN
Two bicyclic depsipeptides, salinamide A (38) and B (39), were produced by a Streptomyces sp., isolated from the surface of the jellyfish Cassiopeia xamachana.
They are potent topical anti-inflammatory in chemically induced mouse ear oedema assays[66,67].
1.4.2.1 Newly Described Metabolites from Marine Bacteria
Since the beginning of this century nearly 250-300 marine bacterial compounds have been described. Interestingly, within the same period the number of described metabolites produced by terrestrial bacteria did not exceed 150 compounds (Laatsch, pers. Comm.). Nearly 100 marine compounds from bacterial origin were isolated within the year 2004, most of them are belonging to actinomycetes. For example, chandrananimycins A-C (40a-c), novel anticancer and antibacterial agents, were iso-lated in our research group from Actinomadura sp.[68].
N O
NH R O
R'
N O
NH O
O CH3
C H3
Br Br
OH OH
Br Br
40a: R = COCH3, R' = OH; 40c 41
40b: R = COCH2OH, R' = H
N
N
N
N O N
N
H NH
NH
S O
O O O O
H O
H H
42
MC21-A (41), a brominated anti-MRSA, was isolated from the new species Pseudoalteromonas phenolica. It rapidly permeabilizes the cell membranes of MRSA, while it has no lytic activity against bacterial cells or human erythrocytes[69]. Mechercharmycin A (42), a cyclic-peptide, was recently isolated from the bacterium
Thermoactinomyces sp. and shows a cytotoxic activity against human lung carci-noma and human leukaemia[70].
Salinosporamide A (43), a highly cytotoxic proteasome inhibitor, was isolated from Salinospora sp. representing one of the remarkable studies in this century. This new genus belongs to a group of rare obligate marine actinomycetes isolated from the ocean sediments[71]. The cytotoxic activity of 48 against human colon carcinoma, was attributed to the inhibition of the 20S proteasome[72]. Moreover, sporolides A-B (44, 45), halogenated macrolides, were isolated from Salinospora tropica[73].
NH
The marine Salegentibacter sp. T436 from the Eastern Weddell Sea delivered 20 nitro-derivatives, classified into mono/dinitro-4-hydroxy-phenyl and/ or mono/dini-tro-genistein derivatives (46a~53)[74-77]. Most of the 20 compounds exhibited an ac-tivity against Gram-positive bacteria.
R
R
Despite of the high interesting metabolites delivered from marine derived bacte-ria, several restrictions are present: a) less than 5% of marine bacteria isolated from marine samples are amenable to be cultured on the bases of normal microbiological techniques[78], b) taxonomy of the marine bacteria is very poorly defined, c) The af-forded yields of bacterial extracts are very low, and in some cases, they are below 1 mg/litre. To overcome such complications, microbiologists developed PCR-based screening assays. This technique might be able to increase the screening efficiency for bioactive compounds. Furthermore, the knowledge of genes involved in the bio-synthesis of secondary metabolites has been enlarged. Consequently, understanding of different biosynthetic systems (e.g. polyketide synthetases (PKS), nonribosomal polypeptide synthetases (NRPSs), halogenases) allows new approaches, such as combinatorial biosynthesis. Such insight led to the discovery of the bacterial origin of bryostatins[79]. Additionally, novel antibiotics have been explored as the discovery of recent numerous techniques are able to elucidate the metabolites structures much easier[80,81].
1.4.2.2 Marine Metabolites from North Sea Bacteria
The German North Sea is a special ecological area due to the dynamic tidal wa-ter. Therefore, its microbiological and chemical features might be differ from those of other marine environments[82]. Screening of numerous crude extracts of North Sea
bacteria on the bases of agar diffusion and toxicity tests against brine shrimps as well as human cell lines showed significant activities. Structures of most of the isolated metabolites were, however, not complex and seem to be derived from the amino acid pathways.
The isolation of a new nucleoside, 3´-acetoxy-2´deoxythimidine (54), from strain Bio134, and of the plant metabolite isoxanthohumol (55) from the bacterium Pic009 were reported in our research group[83]. The latter (55) is known for its anti-carcinogenic and antifungal properties. Moreover, two new antibacterial agents, qui-noline-2-one-4-carboxylic acid methyl ester (56) and 3-pyridinecarboxamide (58) were obtained from the strain Hel59b[83]. Two new indole alkaloids, 3,3-bis-(3-indolyl)-butan-2-one (59) and 3,3',3"-trisindolyl-methane (60) were also reported from Vibrio parahaemolyticus Bio249 by our group[84].
N
Zeeck and his co-workers[82] reported the isolation of tropodithietic acid (57), a sulphur containing compound. This was together with 3-(4´-hydroxyphenyl)-4-phenylpyrol-2,5-dicarcoxylic acid (62) and 3,4-di(4´-hydroxyphenyl)
pyrrole-2,5-dicarcoxylic (63) from the strain RK377. Bacteriopheophytin aL (61) was isolated by the same research group for the first time from a marine bacterial strain.
N