Culture conditions for the production of an acidic exopolysaccharide by the nitrogen-fixing bacterium Burkholderia tropica

The cepacian-like exopolysaccharide of Paraburkholderia ultramafica STM10279T enhances growth and metal adaptation of Tetraria comosa on New Caledonian ultramafic soil

Paraburkholderia ultramafica STM10279T is a metal-tolerant rhizobacterium that promotes plant growth. It was isolated from the roots of Tetraria arundinaceae, a pioneer endemic tropical herb growing on ultramafic soils in New Caledonia. We have recently shown that the main mechanism of metal tolerance of P. ultramafica is related to the production of an acidic exopolysaccharide (EPS). To explore the potential role of this EPS in the plant's environmental adaptation, we first elucidated its structure by employing a combination of chromatography and mass spectrometry techniques. These analyses revealed that the EPS is highly branched and composed of galactosyl (35.8%), glucosyl (33.2%), rhamnosyl (19.5%), mannosyl (7.2%), and glucuronosyl residues (4.4%), similar to the EPS of the Burkholderia cepacia complex known as cepacian. We subsequently conducted greenhouse experiments on Tetraria comosa plantlets inoculated with P. ultramafica or a solution of its EPS during transplanting onto ultramafic substrate. The data showed that the dry weight of T. comosa shoots was 2.5 times higher in the plants treated with the EPS compared to the unexposed plants. In addition, inductively coupled plasma-optical emission spectrometry (ICP-OES) analysis revealed that exposure to the EPS significantly increased Ca, Mg, K, and P uptake as well as K content in roots. In vitro experiments using the Pikovskaya method showed that the EPS was able to solubilize phosphorus. Consistent with the retention of metals in roots and a reduction in shoots, our data revealed a significant decrease in metal translocation factors (TFs) in the plants inoculated with the EPS. These results suggest a beneficial effect of the rhizobacterial EPS on plant growth and abiotic stress mitigation. In addition, the data suggest that the reduced levels of trace metals in plants exposed to P. ultramafica STM10279T are due to metal chelation by the EPS. Further investigations are needed to firmly demonstrate whether this EPS could be used as a biostimulant for plant growth and adaptation to ultramafic soils.

The Exopolysaccharide Cepacian Plays a Role in the Establishment of the Paraburkholderia phymatum - Phaseolus vulgaris Symbiosis

Paraburkholderia phymatum is a rhizobial strain that belongs to the beta-proteobacteria, a group known to form efficient nitrogen-fixing symbioses within root nodules of several legumes, including the agriculturally important common bean. The establishment of the symbiosis requires the exchange of rhizobial and plant signals such as lipochitooligosaccharides (Nod factors), polysaccharides, and flavonoids. Inspection of the genome of the competitive rhizobium P. phymatum revealed the presence of several polysaccharide biosynthetic gene clusters. In this study, we demonstrate that bceN, a gene encoding a GDP-D-mannose 4,6-dehydratase, which is involved in the production of the exopolysaccharide cepacian, an important component of biofilms produced by closely related opportunistic pathogens of the Burkholderia cepacia complex (Bcc), is required for efficient plant colonization. Wild-type P. phymatum was shown to produce cepacian while a bceN mutant did not. Additionally, the bceN mutant produced a significantly lower amount of biofilm and formed less root nodules compared to the wild-type strain with Phaseolus vulgaris as host plant. Finally, expression of the operon containing bceN was induced by the presence of germinated P. vulgaris seeds under nitrogen limiting conditions suggesting a role of this polysaccharide in the establishment of this ecologically important symbiosis.

Fermentation conditions optimization, purification, and antioxidant activity of exopolysaccharides obtained from the plant growth-promoting endophytic actinobacterium Glutamicibacter halophytocola KLBMP 5180

In this study, an endophytic actinobacterium Glutamicibacter halophytocola KLBMP 5180, was investigated for the production and antioxidant activity of exopolysaccharides (EPSs). First, the suitable fermentation time, temperature, inoculation volume, pH value, and the carbon and nitrogen sources for EPSs production were obtained using the one variable at a time method (OVAT). Then, a central composition design was used for fermentation conditions optimization to obtain the maximum EPS yield. The optimal medium and condition were as follows: 100 mL broth in 250 mL Erlenmeyer flasks, including 3.65 g/L maltose, 9.88 g/L malt extract, 3.40 g/L yeast extract, 1.41 g/L MnCl₂, pH 7.5, culture temperature 28 °C, and 200 rpm for 7 days, which increased the yield of EPSs to 2.89 g/L. Two purified EPSs, 5180EPS-1 (MW 58.9 kDa) and 5180EPS-2 (10.5 kDa), comprising rhamnose, galacturonic acid, glucose, glucuronic acid, xylose, and arabinose, were obtained for chemical analysis and antioxidant evaluation. The scavenging ability and reducing power of the superoxide anion and hydroxyl radicals demonstrated the moderate in vitro antioxidant activities of the two EPSs, thus indicating their potential to be a new source of natural antioxidants. However, further structure elucidation and functional studies need to be continued.

Polysaccharides from Burkholderia species as targets for vaccine development, immunomodulation and chemical synthesis

Covering: up to 2018 Burkholderia species are a vast group of human pathogenic, phytopathogenic, and plant- or environment-associated bacteria. B. pseudomallei, B. mallei, and B. cepacia complex are the causative agents of melioidosis, glanders, and cystic fibrosis-related infections, respectively, which are fatal diseases in humans and animals. Due to their high resistance to antibiotics, high mortality rates, and increased infectivity via the respiratory tract, B. pseudomallei and B. mallei have been listed as potential bioterrorism agents by the Centers for Disease Control and Prevention. Burkholderia species are able to produce a large network of surface-exposed polysaccharides, i.e., lipopolysaccharides, capsular polysaccharides, and exopolysaccharides, which are virulence factors, immunomodulators, major biofilm components, and protective antigens, and have crucial implications in the pathogenicity of Burkholderia-associated diseases. This review provides a comprehensive and up-to-date account regarding the structural elucidation and biological activities of surface polysaccharides produced by Burkholderia species. The chemical synthesis of oligosaccharides mimicking Burkholderia polysaccharides is described in detail. Emphasis is placed on the recent research efforts toward the development of glycoconjugate vaccines against melioidosis and glanders based on synthetic or native Burkholderia oligo/polysaccharides.

Characterization of biofilm production by Pseudomonas fluorescens isolated from refrigerated raw buffalo milk

Pseudomonas fluorescens can often be isolated from refrigerated raw milk. Two strains of P. fluorescens PL5.4 and PL7.1, isolated from raw buffalo milk, were evaluated for their proteolytic capacity, exopolysaccharide production and biofilm production. Proteolytic activity was observed in both strains. The P. fluorescens PL5.4 strain presented fluorescence in the presence of calcofluor, indicating exopolysaccharide production. Both strains were able to produce biofilm at 7 °C for 72 h. For the biofilm production test on stainless steel, adherent cell counts of up to 7.1, 7.3 and 8.8 log CFU/cm² at 7, 23 and 30 °C were obtained. Through scanning electron microscopy, it was possible to observe the biofilm produced by the P. fluorescens PL5.4 strain. Proper cleaning and disinfection practices in order are important to reduce bacterial contamination and extend the useful life of raw material and its derivatives.

Terrestrial Microorganisms: Cell Factories of Bioactive Molecules with Skin Protecting Applications

It is well known that terrestrial environments host an immense microbial biodiversity. Exposed to different types of stress, such as UV radiation, temperature fluctuations, water availability and the inter- / intra-specific competition for resources, terrestrial microorganisms have been evolved to produce a large spectrum of bioactive molecules. Bacteria, archaea, protists, fungi and algae have shown a high potential of producing biomolecules for pharmaceutical or other industrial purposes as they combine a sustainable, relatively low-cost and fast-production process. Herein, we provide an overview of the different bioactive molecules produced by terrestrial microorganisms with skin protecting applications. The high content in polyphenolic and carotenoid compounds produced by several strains, as well as the presence of exopolysaccharides, melanins, indole and pyrrole derivatives, mycosporines, carboxylic acids and other molecules, are discussed in the context of their antioxidant, photo-protective and skin-whitening activity. Relevant biotechnological tools developed for the enhanced production of high added value natural products, as well as the protecting effect of some antioxidant, hydrolytic and degrading enzymes are also discussed. Furthermore, we describe classes of microbial compounds that are used or have the potential to be used as antimicrobials, moisturizers, biosurfactants, pigments, flavorings and fragrances.

Environmental interactions are regulated by temperature in Burkholderia seminalis TC3.4.2R3

Burkholderia seminalis strain TC3.4.2R3 is an endophytic bacterium isolated from sugarcane roots that produces antimicrobial compounds, facilitating its ability to act as a biocontrol agent against phytopathogenic bacteria. In this study, we investigated the thermoregulation of B. seminalis TC3.4.2R3 at 28 °C (environmental stimulus) and 37 °C (host-associated stimulus) at the transcriptional and phenotypic levels. The production of biofilms and exopolysaccharides such as capsular polysaccharides and the biocontrol of phytopathogenic fungi were enhanced at 28 °C. At 37 °C, several metabolic pathways were activated, particularly those implicated in energy production, stress responses and the biosynthesis of transporters. Motility, growth and virulence in the Galleria mellonella larvae infection model were more significant at 37 °C. Our data suggest that the regulation of capsule expression could be important in virulence against G. mellonella larvae at 37 °C. In contrast, B. seminalis TC3.4.2R3 failed to cause death in infected BALB/c mice, even at an infective dose of 10⁷ CFU.mL^-1. We conclude that temperature drives the regulation of gene expression in B. seminalis during its interactions with the environment.

Degradation of crude oil by mixed cultures of bacteria isolated from the Qinghai-Tibet plateau and comparative analysis of metabolic mechanisms

This study investigates the biodegradation of crude oil by a mixed culture of bacteria isolated from the Qinghai-Tibet plateau using gas chromatography-mass spectrometer (GC-MS) and the gravimetric method. The results showed that a mixed culture has a stronger ability to degrade hydrocarbon than pure cultures. Once both Nocardia soli Y48 and Rhodococcus erythropolis YF28-1 (8) were present in a culture, the culture demonstrated the highest crude oil removal efficiency of almost 100% after 10 days of incubation at 20 °C. Moreover, further analysis of the degradation mechanisms used by the above strains, which revealed utilization of different n-alkane substrates, indicated the diversity of evolution and variations in different strains, as well as the importance of multiple metabolic mechanisms for alkane degradation. Therefore, it is concluded that a mixed culture of Y48 and YF28-1 (8) strains can provide a more effective method for bioremediation of hydrocarbon-contaminated soil in permafrost regions.

Genomic Features and Insights into the Taxonomy, Virulence, and Benevolence of Plant-Associated Burkholderia Species

The members of the Burkholderia genus are characterized by high versatility and adaptability to various ecological niches. With the availability of the genome sequences of numerous species of Burkholderia, many studies have been conducted to elucidate the unique features of this exceptional group of bacteria. Genomic and metabolic plasticity are common among Burkholderia species, as evidenced by their relatively large multi-replicon genomes that are rich in insertion sequences and genomic islands and contain a high proportion of coding regions. Such unique features could explain their adaptability to various habitats and their versatile lifestyles, which are reflected in a multiplicity of species including free-living rhizospheric bacteria, plant endosymbionts, legume nodulators, and plant pathogens. The phytopathogenic Burkholderia group encompasses several pathogens representing threats to important agriculture crops such as rice. Contrarily, plant-beneficial Burkholderia have also been reported, which have symbiotic and growth-promoting roles. In this review, the taxonomy of Burkholderia is discussed emphasizing the recent updates and the contributions of genomic studies to precise taxonomic positioning. Moreover, genomic and functional studies on Burkholderia are reviewed and insights are provided into the mechanisms underlying the virulence and benevolence of phytopathogenic and plant-beneficial Burkholderia, respectively, on the basis of cutting-edge knowledge.

Synergistic degradation of crude oil by indigenous bacterial consortium and exogenous fungus Scedosporium boydii

The purpose of this study was to investigate the potential of defined co-culture of indigenous bacterial consortium and exogenous fungus Scedosporium boydii for biodegradation of crude oil. After 7 days of incubation, residual oil, n-alkanes and aromatic fraction were analyzed. The degradation rate of crude oil was increased from 61.06% to 81.45% by the defined co-culture according to the 3:1 inoculation ratio of bacteria to fungi. The microbial activity was enhanced markedly and the formation of biofilms was accelerated after suitable inoculation of Scedosporium boydii. High throughput analysis showed that bacterial evenness and diversity were increased and the relative abundance of Paraburkholderia tropica was increased observably from 7.67% to 56.13% in the defined co-culture. These results indicated that synergistic degradation of crude oil in the bacteria-fungi consortium may be advantageous for bioremediation of petroleum-contaminated site.

Structural studies of an exopolysaccharide produced by Gluconacetobacter diazotrophicus Pal5

Gluconacetobacter diazotrophicus is a nitrogen-fixing bacterium that has been found colonizing several plants. This acid-tolerant bacterium produces phytohormones that promote plant growth and is also able to grow in high-sugar concentrations. It has been demonstrated that exopolysaccharides (EPS), which are produced by strain Pal5 of G. diazotrophicus, play an important role in plant infection. We have investigated the structure of the EPS, which was produced by a strain of Pal5 grown in liquid medium containing mannitol as the sole carbon source. The results reveal an EPS with Glc, Gal, Man in a molar ratio of 6:3:1, respectively. NMR spectroscopy and chemical derivatization have revealed that the EPS structure has 4-O-substituted units of β-glucose, 3-O-substituted units of β-galactose and 2-O-substituted units of α-mannose. Glucose and galactose units linked at C6 were also found. The structure proposed herein is different from EPS produced by other species of Gluconacetobacter published to date.

Monitoring bacterial twitter: does quorum sensing determine the behavior of water and wastewater treatment biofilms?

Bacteria have their own form of "twitter" communication, described as quorum sensing (QS), where bacteria emit and sense chemical signal molecules as a means to gauge population density and control gene expression. Many QS-controlled genes relate to biofilm formation and function and may be important for some water and wastewater treatment biofilms. There is a need to better understand bacterial QS, the bacteria biofilm aspects influenced by QS in engineered reactors, and to assess how designs and operations might be improved by taking this signaling into account. This paper provides a critical review of QS and how it relates to biofilms in engineered water and wastewater treatment systems and identifies needs for future research.

Common features of environmental and potentially beneficial plant-associated Burkholderia

The genus Burkholderia comprises more than 60 species isolated from a wide range of niches. Although they have been shown to be diverse and ubiquitously distributed, most studies have thus far focused on the pathogenic species due to their clinical importance. However, the increasing number of recently described Burkholderia species associated with plants or with the environment has highlighted the division of the genus into two main clusters, as suggested by phylogenetical analyses. The first cluster includes human, animal, and plant pathogens, such as Burkholderia glumae, Burkholderia pseudomallei, and Burkholderia mallei, as well as the 17 defined species of the Burkholderia cepacia complex, while the other, more recently established cluster comprises more than 30 non-pathogenic species, which in most cases have been found to be associated with plants, and thus might be considered to be potentially beneficial. Several species from the latter group share characteristics that are of use when associating with plants, such as a quorum sensing system, the presence of nitrogen fixation and/or nodulation genes, and the ability to degrade aromatic compounds. This review examines the commonalities in this growing subgroup of Burkholderia species and discusses their prospective biotechnological applications.