Phenylnannolones A-C: Biosynthesis of New Secondary Metabolites from the MyxobacteriumNannocystis exedens

Industrial and Pharmaceutical Applications of Microbial Diversity of Hypersaline Ecology from Lonar Soda Crater

The unidentified geochemical and physiochemical characteristics of Soda Lakes across the globe make it a novel reservoir and bring attention to scientific civic for its conceivable industrial and pharmaceutical applications. In India, in the Maharashtra state, Lonar Lake is a naturally created Soda Lake by a meteorite impact. Phylogenetic data from this lake explored a diverse array of microorganisms like haloalkaliphilic bacteria and Archaea. Previously reported studies postulated the major microbial communities present in this lake ecosystem are Proteobacteria, Actinobacteria, Firmicutes, and Cyanobacteria. Furthermore, it also contains Bacteroidetes, Nitrospirae, and Verrucomicrobia. This lake is also rich in phytoplankton, with the predominant presence of the Spirulina plantensis. Unique microbial strains from Lonar Lake ecosystems have fascinated consideration as a source of biological molecules with medicinal, industrial, and biotechnological potential. Recent literature revealed the isolation of antibioticproducing bacteria and alkaline proteases-producing alkaliphilic bacterium, as well as novel species of rare methylotrophs, other bacterial strains involved in producing vital enzymes, and unique actinomycetes are also reported. It indicates that the novel bacterial assemblage not reached hitherto may exist in this modified and unique ecology. This comprehensive review provides information about microbial diversity and its industrial and pharmaceutical interests that exist in Lonar Lake, which could be the future source of bioactive enzymes, biosurfactants, and biofuel and also useful in bioremediation. Furthermore, the novel species of microorganisms isolated from Lonar Lake have applications in the biosynthesis of medicines like antibiotics, antivirals, antifungals, anti-inflammatory agents, and precursors for synthesising valuable products. Data consolidated in the present review will cater to the needs of emerging industrial sectors for their commercial and therapeutic applications.

Myxobacteria: biology and bioactive secondary metabolites

Myxobacteria are Gram-negative eubacteria and they thrive in a variety of habitats including soil rich in organic matter, rotting wood, animal dung and marine environment. Myxobacteria are a promising source of new compounds associated with diverse bioactive spectrum and unique mode of action. The genome information of myxobacteria has revealed many orphan biosynthetic pathways indicating that these bacteria can be the source of several novel natural products. In this review, we highlight the biology of myxobacteria with emphasis on their habitat, life cycle, isolation methods and enlist all the bioactive secondary metabolites purified till date and their mode of action.

Metabolic and Biosynthetic Diversity in Marine Myxobacteria

Prior to 2005, the vast majority of characterized myxobacteria were obtained from terrestrial habitats. Since then, several species of halotolerant and even obligate marine myxobacteria have been described. Chemical analyses of extracts from these organisms have confirmed their ability to produce secondary metabolites with unique chemical scaffolds. Indeed, new genera of marine-derived myxobacteria, particularly Enhygromyxa, have been shown to produce novel chemical scaffolds that differ from those observed in soil myxobacteria. Further studies have shown that marine sponges and terrestrial myxobacteria are capable of producing similar or even identical secondary metabolites, suggesting that myxobacterial symbionts may have been the true producers. Recent in silico analysis of the genome sequences available from six marine myxobacteria disclosed a remarkably versatile biosynthetic potential. With access to ever-advancing tools for small molecule and genetic evaluation, these studies suggest a bright future for expeditions into this yet untapped resource for secondary metabolites.

Myxobacterial natural products: An under-valued source of products for drug discovery for neurological disorders

Age-related disorders impose noticeable financial and emotional burdens on society. This impact is becoming more prevalent with the increasing incidence of neurodegenerative diseases and is causing critical concerns for treatment of patients worldwide. Parkinson's disease, Alzheimer's disease, multiple sclerosis and motor neuron disease are the most prevalent and the most expensive to treat neurodegenerative diseases globally. Therefore, exploring effective therapies to overcome these disorders is a necessity. Natural products and their derivatives have increasingly attracted attention in drug discovery programs that have identified microorganisms which produce a large range of metabolites with bioactive properties. Myxobacteria, a group of Gram-negative bacteria with large genome size, produce a wide range of secondary metabolites with significant chemical structures and a variety of biological effects. They are potent natural product producers. In this review paper, we attempt to overview some secondary metabolites synthesized by myxobacteria with neuroprotective activity through known mechanisms including production of polyunsaturated fatty acids, reduction of apoptosis, immunomodulation, stress reduction of endoplasmic reticulum, stabilization of microtubules, enzyme inhibition and serotonin receptor modulation.

Investigating the Biosynthesis of Natural Products from Marine Proteobacteria: A Survey of Molecules and Strategies

The phylum proteobacteria contains a wide array of Gram-negative marine bacteria. With recent advances in genomic sequencing, genome analysis, and analytical chemistry techniques, a whole host of information is being revealed about the primary and secondary metabolism of marine proteobacteria. This has led to the discovery of a growing number of medically relevant natural products, including novel leads for the treatment of multidrug-resistant Staphylococcus aureus (MRSA) and cancer. Of equal interest, marine proteobacteria produce natural products whose structure and biosynthetic mechanisms differ from those of their terrestrial and actinobacterial counterparts. Notable features of secondary metabolites produced by marine proteobacteria include halogenation, sulfur-containing heterocycles, non-ribosomal peptides, and polyketides with unusual biosynthetic logic. As advances are made in the technology associated with functional genomics, such as computational sequence analysis, targeted DNA manipulation, and heterologous expression, it has become easier to probe the mechanisms for natural product biosynthesis. This review will focus on genomics driven approaches to understanding the biosynthetic mechanisms for natural products produced by marine proteobacteria.

Marine-derived myxobacteria of the suborder Nannocystineae: An underexplored source of structurally intriguing and biologically active metabolites

Myxobacteria are famous for their ability to produce most intriguing secondary metabolites. Till recently, only terrestrial myxobacteria were in the focus of research. In this review, however, we discuss marine-derived myxobacteria, which are particularly interesting due to their relatively recent discovery and due to the fact that their very existence was called into question. The to-date-explored members of these halophilic or halotolerant myxobacteria are all grouped into the suborder Nannocystineae. Few of them were chemically investigated revealing around 11 structural types belonging to the polyketide, non-ribosomal peptide, hybrids thereof or terpenoid class of secondary metabolites. A most unusual structural type is represented by salimabromide from Enhygromyxa salina. In silico analyses were carried out on the available genome sequences of four bacterial members of the Nannocystineae, revealing the biosynthetic potential of these bacteria.

Nannozinones and sorazinones, unprecedented pyrazinones from myxobacteria

Nannozinones A (1) and B (2) were discovered as metabolites of the recently isolated Nannocystis pusilla strain MNa10913 belonging to the poorly studied myxobacterial family Nannocystaceae. In contrast, the structurally related sorazinones A (5) and B (6) were isolated from Sorangium cellulosum strain Soce895, which was known as the producer of the antibiotic thuggacin A. The extract also contained methyl indole-3-carboxylate (4). HRESIMS and (1)H, (13)C, and (15)N NMR spectroscopy revealed the structures of nannozinones A (1) and B (2) as unusual dihydropyrrolo- and pyrrolopyrazinone derivatives, while sorazinone A (5) was characterized as an aromatic diketopiperazine and sorazinone B (6) as a dibenzyl 2(1H)-pyrazinone derivative. While the dihydropyrrolo derivative nannozinone A (1) showed weak antibacterial and antifungal activity, nannozinone B (2) inhibited the growth of cell cultures with IC50 values between 2.44 and 16.9 μM. The nannochelin A iron complex (3), which was isolated besides 1 and 2, was even more active, with IC50 values between 0.05 and 1.95 μM. On the other hand, the indole 4 and sorazinones 5 and 6 did not show any significant cytotoxicity and only weak activity against the Gram-positive Nocardia sp.

Pyrronazols, metabolites from the myxobacteria Nannocystis pusilla and N. exedens, are unusual chlorinated pyrone-oxazole-pyrroles

The chlorinated pyrrole-oxazole-pyrones pyrronazol A (1), pyrronazol A2 (2), and pyrronazol B (3) were isolated from Nannocystis pusilla strain Ari7, and two chlorinated pyrrole-oxazole isomers, pyrronazols C1 (4) and C2 (5), were isolated from N. pusilla strain Na a174. HRESIMS, NMR, and X-ray crystallographic analysis was used in the structure elucidation including the absolute configuration of pyrronazol A (1). In addition to pyrronazols, 1,6-phenazine-diol (6) and its glycosyl derivative, 1-hydroxyphenazin-6-yl-α-d-arabinofuranoside (7), were isolated and identified from the culture broth of N. pusilla strain Ari7. When tested for biological activity against bacteria, fungi, and yeasts, 1 showed weak antifungal activity against Mucor hiemalis (MIC 33.3 μg/mL) but no antibacterial activity, while 6 showed weak antibacterial and antifungal activity (MIC 33.3 μg/mL) against some of the strains tested. In cell culture experiments 1 showed no significant cytotoxicity, while 6 was active against several cell lines, especially the human ovarian carcinoma cells SK-OV-3 (LD50 2.59 μM).

Corallorazines from the myxobacterium Corallococcus coralloides

The myxobacterium Corallococcus coralloides is the producer of the antibiotic compound corallopyronin A, which is currently in preclinical evaluation. To obtain suitable amounts of this antibiotic, the production strain C. coralloides B035 was cultured in large volumes, which in the addition to the isolation of the target molecule facilitates the detection of additional metabolites of this myxobacterial strain (corallorazines A-C). Corallorazine A is a new structural type of dipeptide composed of a dehydroalanine and a glycine moiety that are linked via a semiaminal bond, thus forming a piperazine ring. The latter is further connected via an amide bond to an unusual aliphatic acyl chain.

Ecological roles and biotechnological applications of marine and intertidal microbial biofilms

This review is a retrospective of ecological effects of bioactivities produced by biofilms of surface-dwelling marine/intertidal microbes as well as of the industrial and environmental biotechnologies developed exploiting the knowledge of biofilm formation. Some examples of significant interest pertaining to the ecological aspects of biofilm-forming species belonging to the Roseobacter clade include autochthonous bacteria from turbot larvae-rearing units with potential application as a probiotic as well as production of tropodithietic acid and indigoidine. Species of the Pseudoalteromonas genus are important examples of successful surface colonizers through elaboration of the AlpP protein and antimicrobial agents possessing broad-spectrum antagonistic activity against medical and environmental isolates. Further examples of significance comprise antiprotozoan activity of Pseudoalteromonas tunicata elicited by violacein, inhibition of fungal colonization, antifouling activities, inhibition of algal spore germination, and 2-n-pentyl-4-quinolinol production. Nitrous oxide, an important greenhouse gas, emanates from surface-attached microbial activity of marine animals. Marine and intertidal biofilms have been applied in the biotechnological production of violacein, phenylnannolones, and exopolysaccharides from marine and tropical intertidal environments. More examples of importance encompass production of protease, cellulase, and xylanase, melanin, and riboflavin. Antifouling activity of Bacillus sp. and application of anammox bacterial biofilms in bioremediation are described. Marine biofilms have been used as anodes and cathodes in microbial fuel cells. Some of the reaction vessels for biofilm cultivation reviewed are roller bottle, rotating disc bioreactor, polymethylmethacrylate conico-cylindrical flask, fixed bed reactor, artificial microbial mats, packed-bed bioreactors, and the Tanaka photobioreactor.

Valuable processes and products from marine intertidal microbial communities

Microbial communities are ubiquitous in marine intertidal environments. These communities, which grow preferentially as biofilms on natural and artificial surfaces, carry out key processes contributing to the functioning of coastal environments and providing valuable services to human society, including carbon cycling, primary productivity, trophic linkage, and transfer and removal of pollutants. In addition, their surface-associated life style greatly influences the integrity and performance of marine infrastructure and archaeological heritage materials. The fluctuating conditions of the intertidal zone make it an extreme environment to which intertidal biofilm organisms must adapt at varying levels. This requirement has probably favored the development and spread of specific microorganisms with particular physiological and metabolic processes. These organisms may have potential biotechnological utility, in that they may provide novel secondary metabolites, biopolymers, lipids, and enzymes and even processes for the production of energy in a sustainable manner.