Microbial natural products exhibit immense structural diversity and complexity and have captured the attention of researchers for several decades. They have been explored for a wide spectrum of applications, most noteworthy being their prominent role in medicine, and their versatility expands to application as drugs for many diseases. Accessing unexplored environments harboring unique microorganisms is expected to yield novel bioactive metabolites with distinguishing functionalities, which can be supplied to the starved pharmaceutical market. For this purpose the oceans have turned out to be an attractive and productive field. Owing to the enormous biodiversity of marine microorganisms, as well as the growing evidence that many metabolites previously isolated from marine invertebrates and algae are actually produced by their associated bacteria, the interest in marine microorganisms has intensified. Since the majority of the microorganisms are uncultured, metagenomic tools are required to exploit the untapped biochemistry. However, after years of employing metagenomics for marine drug discovery, new drugs are vastly under-represented. While a plethora of natural product biosynthetic genes and clusters are reported, only a minor number of potential therapeutic compounds have resulted through functional metagenomic screening. This review explores specific obstacles that have led to the low success rate. In addition to the typical problems encountered with traditional functional metagenomic-based screens for novel biocatalysts, there are enormous limitations which are particular to drug-like metabolites. We also present how targeted and function-guided strategies, employing modern, and multi-disciplinary approaches have yielded some of the most exciting discoveries attributed to uncultured marine bacteria. These discoveries set the stage for progressing the production of drug candidates from uncultured bacteria for pre-clinical and clinical development.

Polyunsaturated fatty acids are important in maintaining human health. Limitations associated with current sources of ω-3 fatty acids and ω-6 fatty acids, from animal and plant sources, have led to increased interest in microbial production. Marine bacteria may provide a suitable alternative, although the isolation of production strains and the identification of operating conditions must be addressed before manufacturing processes become economically viable. Marine isolate 560 was identified as an eicosapentaenoic acid (EPA) producer via GC/MS. The isolate was initially identified as Vibrio cyclitrophicus by 16S rRNA sequencing. Statistically based experimental designs were applied to the optimisation of medium components and environmental factors for the production of EPA. A Plackett-Burman design was used to screen for the effect of temperature, pH, and media components. Subsequently, the concentrations of NaCl, yeast extract, and peptone, identified as significant factors, were optimised using a central composite design. The predicted optimal combination of media components for maximum EPA production (4.8 mg/g dry weight) was determined as 7.9 g/l peptone, 16.2 g/l NaCl, and 6.2 g/l yeast extract. On transfer of this process to bioreactor cultivation, where a range of pH and DO values were tested, the maximum amount of EPA produced increased to 7.5 mg/g dry weight and 10 % of the total fatty acid.

Polyunsaturated fatty acids (PUFAs), especially eicosapentaenoic acid (EPA), are increasingly attracting scientific attention owing to their significant health-promoting role in the human body. However, the human body lacks the ability to produce them in vivo. The limitations associated with the current sources of ω-3 fatty acids from animal and plant sources have led to increased interest in microbial production. Bacterial isolate 717 was identified as a potential high EPA producer. As an important step in the process development of the microbial PUFA production, the culture conditions at the bioreactor scale were optimised for the isolate 717 using a response surface methodology exploring the significant effect of temperature, pH and dissolved oxygen and the interaction between them on the EPA production. This optimisation strategy led to a significant increase in the amount of EPA produced by the isolate under investigation, where the amount of EPA increased from 9 mg/g biomass (33 mg/l representing 7.6 % of the total fatty acids) to 45 mg/g (350 mg/l representing 25 % of the total fatty acids). To avoid additional costs associated with extreme cooling at large scale, a temperature shock experiment was carried out reducing the overall cooling time from the whole cultivation process to 4 h only prior to harvest. The ability of the organism to produce EPA under the complete absence of oxygen was tested revealing that oxygen is not critically required for the biosynthesis of EPA but the production improved in the presence of oxygen. The stability of the produced oil and the complete absence of heavy metals in the bacterial biomass are considered as an additional benefit of bacterial EPA compared to other sources of PUFA. To our knowledge this is the first report of a bacterial isolate producing EPA with such high yields making the large-scale manufacture much more economically viable.

No abstract

Currently, 80% of global energy is supplied by carbon-based fossil fuels, which has led to concerns over the environmental impact of increasing atmospheric CO2 levels and has sparked ever-growing interest in renewable energy sources.

Available online A B S T R A C TMicrobial Poly-β-hydroxybutyrate (PHB) was the first and the most widespread polymer to be used in the biodegradable polymer industry. The optimization of the Egyptian local bacterial strain Microbacterium sp. WA81 productivity was performed using statistical design of experiment tools. A Plackett-Burman design was carried out to screen the effect of different carbon and different nitrogen sources, each in a separate experiment. Moreover, a subsequent Response Surface Methodology was applied to achieve the maximum PHB productivity at shake flask level. Upon scaling up to a bench top bioreactor run scale (5 L), using the generated medium, the amount of the polymer significantly increased (1.42 g/L), which represented a 78-fold increase of that prior optimization. During the bioreactor run, the preliminary effect of Dissolved Oxygen (DO) was explored, and the levels of carbon and nitrogen uptakes were monitored. In conclusion, the statistical design of experiment tools enabled us to optimize and engineer a growth medium and conditions to enhance PHB productivity by the Egyptian isolate Microbacterium sp. WA81.

No abstract

Bacterial poly-β-hydroxybutyrate (PHB) is a natural, biodegradable polymer, which is accumulated in the cells as an energy reserve materialdue to depletion of nitrogen or phosphorous in the presence of excess carbon source. This polymer is foreseen to possess high industrialpotentiality and excellent alternative to the non-degradable petroleum-based plastics. In this study, we isolated and characterized a localbacterial strain WA81 which accumulated 18mg/L PHB after 72 h growth in mineral salt medium under nitrogen deficiency. The PHB granuleswere detected in the cells using TEM and the genes encode for this polymer were detected by oligonucleotide primers using PCR technology.The 16S rRNA gene nucleotide sequence for this isolate was used to construct a phylogentic tree against all available sequences in the GenBank.The phylogenetic tree data suggested that the closest type strain to the local bacterium is the Microbacterium paraoxydans CF36T and hencewe named it Microbacterium sp. strain WA81. Moreover, the set of enzymes responsible for the PHB biosynthetic pathway and their controllingelements were detected in this local isolate using PCR. The genes encode for the biosynthesis enzymes are phbA (β-ketothiolase), phbB(acetoacetly CoA reductase), phbC (PHB polymerase), while the genes encode for the controlling elements are phbP (phasin), phbZ (PHBdepolymerase). The novelty of this local bacterium lies in its ability to accumulate huge amounts of PHB in its cytoplasm and the presence ofa whole set of genes encode for the PHB biosynthetic and catabolic pathways of this polymer.Int J Appl Sci Biotechnol, Vol 3(2): 143-150 DOI: http://dx.doi.org/10.3126/ijasbt.v3i2.12277