Promotion of antibiotic production by high ethanol, high NaCl concentration, or heat shock in Pseudomonas fluorescens S272

Biosynthesis of 2,4-diacetylphloroglucinol from glucose using engineered Escherichia coli

In order to produce 2,4-diacetylphloroglucinol (2,4-DAPG) in E. coli, the key synthases coding by phlACBD gene cluster from the strain Pseudomonas fluorescens CHA0 were overexpressed in E. coli BL21 (DE3). The marA, phlE and acc genes were also overexpressed to enhance 2,4-DAPG biosynthesis. Then the fermentation conditions were optimized to improve the concentration of 2,4-DAPG. The results showed that the recombinant E. coli could produce few 2,4-DAPG with only the phlACBD gene cluster. The synthetic ability of 2,4-DAPG could be increased by expressing the acc, marA and phlE genes in shake-flasks cultivation. The effects of phloroglucinol, initial pH, temperature and trace elements on 2,4-DAPG biosynthesis were also investigated. Based on the optimal fermentation conditions obtained from the shake-flasks cultivation, fed-batch fermentation of strain Z3 in a 5 L bioreactor was conducted to produce 2,4-DAPG. Finally, the concentration of 2,4-DAPG was 179 mg/L after induction for 36 h by fed-batch fermentation. To the best of our knowledge, this is the highest 2,4-DAPG production reported in E. coli. This work showed the potential application of engineered E. coli to get high production of target compounds.

Antibacterial Activities of Bacteria Isolated from the Marine Sponges Isodictya compressa and Higginsia bidentifera Collected from Algoa Bay, South Africa

Due to the rise in multi-drug resistant pathogens and other diseases, there is renewed interest in marine sponge endosymbionts as a rich source of natural products (NPs). The South African marine environment is rich in marine biota that remains largely unexplored and may represent an important source for the discovery of novel NPs. We first investigated the bacterial diversity associated with five South African marine sponges, whose microbial populations had not previously been investigated, and select the two sponges (Isodictya compressa and Higginsia bidentifera) with highest species richness to culture bacteria. By employing 33 different growth conditions 415 sponge-associated bacterial isolates were cultured and screened for antibacterial activity. Thirty-five isolates showed antibacterial activity, twelve of which exhibited activity against the multi-drug resistant Escherichia coli 1699, implying that some of the bioactive compounds could be novel. Genome sequencing of two of these isolates confirmed that they harbour uncharacterized biosynthetic pathways that may encode novel chemical structures.

Proteomics analysis of Bacillus licheniformis in response to oligosaccharides elicitors

The role of oligosaccharides as biotic elicitors has been recognised in the enhanced production of antibiotics from fungal and bacterial cultures. The yield of bacitracin A in cultures of Bacillus licheniformis was increased after supplementation with oligoguluronate (OG), and mannan oligosaccharides (MO) and its mechanism at transcription level been established already. However, the elicitation mechanism at post transcriptional level has not been reported so far. In this paper we investigate changes in proteomics of B. licheniformis in presence of the oligosaccharide elicitors OG and MO. Differentially expressed proteins were examined using 2D-PAGE stained with colloidal Coomassie and were further identified by LC-MS/MS. We identified 19 differentially expressed proteins including those involved in carbon metabolism, energy generation, amino acid biosynthesis, oxidative and general stress response. The novel findings of this work, together with previous reports, contribute to the unravelling of the overall mechanism of elicitation in B. licheniformis cultures and reliability of the use of these elicitors for potential industrial application.

Enhancement of validamycin A production by addition of ethanol in fermentation of Streptomyces hygroscopicus 5008

The effect of ethanol on the production of the important agro-antibiotic validamycin A (Val-A) in medium containing agricultural by-products was investigated. Under the optimal condition of ethanol addition, the maximal Val-A production titer reached 18 g/L, which increased by 60% compared to the control. To provide an insight into cell response to ethanol, the intracellular reactive oxygen species (ROS), gene transcription and enzyme activity were determined. Intracellular ROS as the molecular signal was increased in the ethanol condition. Global regulators afsR and glnR were involved in regulation of Val-A biosynthesis, and the transcription of eight Val-A structural genes was enhanced. The activity of glucose-6-phosphate dehydrogenase (G6PD) was enhanced while glyceraldehyde 3-phosphate dehydrogenase (GAPDH) was inhibited. A signal transduction cascade from cell signal response to activated transcription of Val-A biosynthetic genes and enhanced antibiotic production is proposed. The information can be helpful for the improvement of large-scale fermentation.

Biosynthesis of phloroglucinol compounds in microorganisms--review

Phloroglucinol derivatives are a major class of secondary metabolites of wide occurrence in biological systems. In the bacteria kingdom, these compounds can only be synthesized by some species of Pseudomonads. Pseudomonas spp. could produce 2,4-diacetylphloroglucinol (DAPG) that plays an important role in the biological control of many plant pathogens. In this review, we summarize knowledge about synthesis of phloroglucinol compounds based on the DAPG biosynthetic pathway. Recent advances that have been made in understanding phloroglucinol compound biosynthesis and regulation are highlighted. From these studies, researchers have identified the biosynthesis pathway of DAPG. Most of the genes involved in the biosynthesis pathway have been cloned and characterized. Additionally, heterologous systems of the model microorganism Escherichia coli are constructed to produce phloroglucinol. Although further work is still required, a full understanding of phloroglucinol compound biosynthesis is almost within reach. This review also suggests new directions and attempts to gain some insights for better understanding of the biosynthesis and regulation of DAPG. The combination of traditional biochemistry and molecular biology with new systems biology and synthetic biology tools will provide a better view of phloroglucinol compound biosynthesis and a greater potential of microbial production.

Manipulation of quorum sensing regulation in Pseudomonas fluorescens NCIMB 10586 to increase mupirocin production

Transcription of the 74 kb Pseudomonas fluorescens mupirocin [pseudomonic acid (PA)] biosynthesis cluster depends on quorum sensing-dependent regulation via the LuxI/LuxR homologues MupI/MupR. To facilitate analysis of novel PAs from pathway mutants, we investigated factors that affect mup gene expression. First, the signal produced by MupI was identified as N-(3-oxodecanoyl)homoserine lactone, but exogenous addition of this molecule did not activate mupirocin production prematurely nor did expression of mupI in trans increase metabolite production. Second, we confirmed that mupX, encoding an amidase/hydrolase that can degrade N-acylhomoserine lactones, is also required for efficient expression, consistent with its occurrence in a regulatory module linked to unrelated genes in P. fluorescens. Third, and most significantly, mupR expression in trans to wild type and mutants can increase production of antibiotic and novel intermediates up to 17-fold.

Production of streptomycin from chitin using Streptomyces griseus in bioreactors of different configuration

Streptomyces griseus was cultured in three different bioreactors in a medium containing chitin flakes. When a conventional bioreactor stirred by two sets of Rushton impellers and operated at high speed was used, the yield of streptomycin (3.1mg/l) was the highest observed and occurred at approximately 500 h. Cultivation of S. griseus in a bioreactor stirred at low speed by a U-shaped paddle resulted in a lower yield of streptomycin (1.8 mg/l) but this was achieved in a shorter period of time (400 h). Increasing the concentration of chitin from 5% to 10% w/v had no significant effect on either of these two parameters. The use of a novel vertical basket bioreactor in which the chitin flakes were contained within a wire mesh basket and were gently fluidised by air, enabled comparatively high yields of streptomycin (2.8 mg/l) in the relatively short time of 300 h.

Microbial antibiotic production aboard the International Space Station

Previous studies examining metabolic characteristics of bacterial cultures have mostly suggested that reduced gravity is advantageous for microbial growth. As a consequence, the question of whether space flight would similarly enhance secondary metabolite production was raised. Results from three prior space shuttle experiments indicated that antibiotic production was stimulated in space for two different microbial systems, albeit under suboptimal growth conditions. The goal of this latest experiment was to determine whether the enhanced productivity would also occur with better growth conditions and over longer durations of weightlessness. Microbial antibiotic production was examined onboard the International Space Station during the 72-day 8A increment. Findings of increased productivity of actinomycin D by Streptomyces plicatus in space corroborated with previous findings for the early sample points (days 8 and 12); however, the flight production levels were lower than the matched ground control samples for the remainder of the mission. The overall goal of this research program is to elucidate the specific mechanisms responsible for the initial stimulation of productivity in space and translate this knowledge into methods for improving efficiency of commercial production facilities on Earth.

Regulation of antibiotic production in root-colonizing Peudomonas spp. and relevance for biological control of plant disease

Certain strains of fluorescent pseudomonads are important biological components of agricultural soils that are suppressive to diseases caused by pathogenic fungi on crop plants. The biocontrol abilities of such strains depend essentially on aggressive root colonization, induction of systemic resistance in the plant, and the production of diffusible or volatile antifungal antibiotics. Evidence that these compounds are produced in situ is based on their chemical extraction from the rhizosphere and on the expression of antibiotic biosynthetic genes in the producer strains colonizing plant roots. Well-characterized antibiotics with biocontrol properties include phenazines, 2,4-diacetylphloroglucinol, pyoluteorin, pyrrolnitrin, lipopeptides, and hydrogen cyanide. In vitro, optimal production of these compounds occurs at high cell densities and during conditions of restricted growth, involving (i) a number of transcriptional regulators, which are mostly pathway-specific, and (ii) the GacS/GacA two-component system, which globally exerts a positive effect on the production of extracellular metabolites at a posttranscriptional level. Small untranslated RNAs have important roles in the GacS/GacA signal transduction pathway. One challenge in future biocontrol research involves development of new strategies to overcome the broad toxicity and lack of antifungal specificity displayed by most biocontrol antibiotics studied so far.

Biological activity of secondary metabolites produced by a strain of Pseudomonas fluorescens

Biological activity of secondary metabolites produced by a plant-growth-promoting Pseudomonas fluorescens was evaluated. The strain produced antibiotics phenazine (PHE), 2,4-diacetylphloroglucinol (PHL) and siderophore pyoverdin (PYO) in standard King's B and succinic acid media, respectively. After extraction, PYO was identified by comparing the UV-spectra and moss-green color development after 'diazotized sulfanilic acid' (DSA) spray in TLC. PHE and PHL were identified by comparing standard compounds on TLC and orange-color development immediately after DSA spray. In vitro antibiosis study of the metabolites revealed their antibacterial and antifungal activity against bacterial test organisms Corynebacterium sp., Mycobacterium phlei and M. smegmatis and test fungi Fusarium moniliforme, F. oxysporum, F. semitectum, F. solani and Rhizoctonia solani. A statistically significantly higher plant growth was recorded in siderophore-amended plantlets under gnotobiotic conditions whereas PHE and PHL did not show any plant-growth-promoting activity. These results support the importance of the secondary metabolites produced by the strain P. fluorescens in enhancing plant growth and in controlling fungal and bacterial pathogens.

Secondary metabolism in simulated microgravity

We have studied microbial secondary metabolism in a simulated microgravity (SMG) environment provided by NASA rotating-wall bioreactors (RWBs). These reactors were designed to simulate some aspects of actual microgravity that occur in space. Growth and product formation were observed in SMG in all cases studied, i.e., Bacillus brevis produced gramicidin S (GS), Streptomyces clavuligerus made beta-lactam antibiotics, Streptomyces hygroscopicus produced rapamycin, and Escherichia coli produced microcin B17 (MccB17). Of these processes, only GS production was unaffected by SMG; production of the other three products was inhibited. This was determined by comparison with performance in an RWB positioned in a different mode to provide a normal gravity (NG) environment. Carbon source repression by glycerol of the GS process, as observed in shaken flasks, was not observed in the RWBs, whether operated in the SMG or NG mode. The same phenomenon occurred in the case of MccB17 production, with respect to glucose repression. Thus, the negative effects of carbon source on GS and beta-lactam formation are presumably dependent on shear, turbulence, and/or vessel geometry, but not on gravity. Stimulatory effects of phosphate and the precursor L-lysine on beta-lactam antibiotic production, as observed in flasks, also occurred in SMG. An almost complete shift in the localization of produced MccB17 from cells to extracellular medium was observed when E. coli was grown in the RWB under SMG or NG. If a plastic bead was placed in the RWB, accumulation became cellular, as it is in shaken flasks, indicating that sheer stress favors a cellular location. In the case of rapamycin, the same type of shift was observed, but it was less dramatic, i.e., growth in the RWB under SMG shifted the distribution of produced rapamycin from 2/3 cellular:1/3 extracellular to 1/3 cellular:2/3 extracellular. Stress has been shown to induce or promote secondary metabolism in a number of other microbial systems. RWBs provide a low stress SMG environment, which, however, supports only poor production of MccB17, as compared to production in shaken flasks. We wondered whether the poor production in RWBs under SMG is due to the low level of stress, and whether increasing stress in the RWBs would raise the amount of MccB17 formed. We found that increasing shear stress by adding a single Teflon bead to the RWB improved MccB17 production. Although shear stress seems to have a marked positive effect on MccB17 production in SMG, addition of various concentrations of ethanol to RWBs (or to shaken flasks) failed to increase MccB17 production. Ethanol stress merely decreased production and, at higher concentrations, inhibited growth. Interestingly, cells growing in the RWB were much more resistant to the growth- and production-inhibitory effects of ethanol than cells growing in shaken flasks. With respect to S. hygroscopicus, addition of Teflon beads to the RWB reversed the inhibition of growth, but rapamycin production was still markedly inhibited, and the distribution did not revert back to a preferential cellular site.

Structural analysis of an extracellular polysaccharide bioflocculant of Klebsiella pneumoniae

The glycoside composition and sequence of an extracellular polysaccharide flocculant of Klebsiella pneumoniae H12 was analyzed. GC and HPLC analysis of the acid-hydrolysate identified its constituent monosaccharides as D-Glc, D-Man, D-Gal, and D-GlcA in an approximate molar ratio of 3.9:1.0:2.3:3.6. To analyze the glycoside sequence, the polysaccharide was partially hydrolyzed by acid and enzyme treatment. GC, HPLC, TLC, MALDI-TOF/MS, and 1H- and 13C- NMR spectroscopy characterized the obtained oligosaccharides. The results clarified the partial structure of H12 polysaccharide as a linear polymer of a unit of pentasaccharide with a side chain of one D-GlcA to D-Glc moiety (see below). Although the existence of other sequences or other constituent glycosides could not be fully excluded, H12 polysaccharide must be a novel types as such a complicated unit for a polymer has not so far been reported. The partial structure of a H12 polysaccharide flocculant is also discussed in this report. [structure: see text]

Quorum-sensing in Gram-negative bacteria

It has become increasingly and widely recognised that bacteria do not exist as solitary cells, but are colonial organisms that exploit elaborate systems of intercellular communication to facilitate their adaptation to changing environmental conditions. The languages by which bacteria communicate take the form of chemical signals, excreted from the cells, which can elicit profound physiological changes. Many types of signalling molecules, which regulate diverse phenotypes across distant genera, have been described. The most common signalling molecules found in Gram-negative bacteria are N-acyl derivatives of homoserine lactone (acyl HSLs). Modulation of the physiological processes controlled by acyl HSLs (and, indeed, many of the non-acyl HSL-mediated systems) occurs in a cell density- and growth phase-dependent manner. Therefore, the term 'quorum-sensing' has been coined to describe this ability of bacteria to monitor cell density before expressing a phenotype. In this paper, we review the current state of research concerning acyl HSL-mediated quorum-sensing. We also describe two non-acyl HSL-based systems utilised by the phytopathogens Ralstonia solanacearum and Xanthomonas campestris.

Enhancement of plant stem growth by flocculation of the antibiotic-producing bacterium, Pseudomonas fluorescens S272, on the roots

The antibiotic-producing bacterium, Pseudomonas fluorescens, is assumed to be important in protecting plants from soilborne diseases. S. fluorescens S272, a hyper-producing strain of pyoluteorin (PT) and 2,4-diacetylphloroglucinol (DG), had previously been isolated from soil. The present paper reported that the growth of water-cultivated Kaiware radish was promoted to 120-140% of its normal level by the coaddition of an S272 culture broth (0.01-1% v/v) and a polysaccharide flocculant (1-100 ppm) from Klebsiella pneumoniae H12. Tight adhesion of S272 cells to the root tissue was microscopically observed. The growth promotion is assumed to have been caused by antibiotic effects for the following two reasons: 1) PT (4 mg/l) and DG (24 mg/l) addition to a radish culture enhanced stem growth to 130% of the normal level; 2) a culture solution containing the S272 culture broth (0.01-1% v/v) markedly inhibited the decomposition of hypersensitive chrysanthemum leaves. A soil-cultivation experiment with Gomphrena globosa under natural conditions also exhibited enhanced stem length (160%) by coaddition of the S272 culture broth and H12 polysaccharide. These results suggest that polysaccharide-enhanced adhesion of P. fluorescens S272 cells might be useful for promoting plant growth through the increased antibiotic effect.