Antimicrobial and anti-biofilm activities of Bi subnitrate and BiNPs produced by Delftia sp. SFG against clinical isolates of Staphylococcus aureus, Pseudomonas aeruginosa, and Proteus mirabilis.

In the present study Delftia sp. Shakibaie, Forootanfar, and Ghazanfari (SFG), was applied for preparation of biogenic Bi nanoparticles (BiNPs) and antibacterial and anti-biofilm activities of the purified BiNPs were investigated by microdilution and disc diffusion methods. Transmission electron micrographs showed that the produced nanostructures were spherical with a size range of 40-120 nm. The measured minimum inhibitory concentration of both the Bi subnitrate and BiNPs against three biofilms producing bacterial pathogens of Staphylococcus aureus, Pseudomonas aeruginosa, and Proteus mirabilis were found to be above 1280 µg/ml. Addition of BiNPs (1000 µg/disc) to antibiotic discs containing tobramycin, nalidixic acid, ceftriaxone, bacitracin, cefalexin, amoxicillin, and cefixime significantly increased the antibacterial effects against methicillin-resistant S. aureus (MRSA) in comparison with Bi subnitrate (p < 0.05). Furthermore, the biogenic BiNPs decreased the biofilm formation of S. aureus, P. aeruginosa, and P. mirabilis to 55, 85, and 15%, respectively. In comparison to Bi subnitrate, BiNPs indicated significant anti-biofilm activity against P. aeruginosa (p < 0.05) while the anti-biofilm activity of BiNPs against S. aureus and P. mirabilis was similar to that of Bi subnitrate. To sum up, the attained results showed that combination of biogenic BiNPs with commonly used antibiotics relatively enhanced their antibacterial effects against MRSA.

Anti-quorum Sensing and Anti-biofilm Activity of Delftia tsuruhatensis Extract by Attenuating the Quorum Sensing-Controlled Virulence Factor Production in Pseudomonas aeruginosa.

Multidrug-resistance bacteria commonly use cell-to-cell communication that leads to biofilm formation as one of the mechanisms for developing resistance. Quorum sensing inhibition (QSI) is an effective approach for the prevention of biofilm formation. A Gram-negative bacterium, Delftia tsuruhatensis SJ01, was isolated from the rhizosphere of a species of sedge (Cyperus laevigatus) grown along the coastal-saline area. The isolate SJ01 culture and bacterial crude extract showed QSI activity in the biosensor plate containing the reference strain Chromobacterium violaceum CV026. A decrease in the violacein production of approximately 98% was detected with the reference strain C. violaceum CV026. The bacterial extract (strain SJ01) exhibited anti-quorum sensing activity and inhibited the biofilm formation of clinical isolates wild-type Pseudomonas aeruginosa PAO1 and P. aeruginosa PAH. A non-toxic effect of the bacterial extract (SJ01) was detected on the cell growth of the reference strains as P. aeruginosa viable cells were present within the biofilm. It is hypothesized that the extract (SJ01) may change the topography of the biofilm and thus prevent bacterial adherence on the biofilm surface. The extract also inhibits the motility, virulence factors (pyocyanin and rhamnolipid) and activity (elastase and protease) in P. aeruginosa treated with SJ01 extract. The potential active compound present was identified as 1,2-benzenedicarboxylic acid, diisooctyl ester. Microarray and transcript expression analysis unveiled differential expression of quorum sensing regulatory genes. The key regulatory genes, LasI, LasR, RhlI, and RhlR were down-regulated in the P. aeruginosa analyzed by quantitative RT-PCR. A hypothetical model was generated of the transcriptional regulatory mechanism inferred in P. aeruginosa for quorum sensing, which will provide useful insight to develop preventive strategies against the biofilm formation. The potential active compound identified, 1,2-benzenedicarboxylic acid, diisooctyl ester, has the potential to be used as an anti-pathogenic drug for the treatment of biofilm-forming pathogenic bacteria. For that, a detailed study is needed to investigate the possible applications.

Unusual poly(3-hydroxyalkanoate) (PHA) biosynthesis behavior of Pseudomonas putida Bet001 and Delftia tsuruhatensis Bet002 isolated from palm oil mill effluent.

Pseudomonas putida Bet001 and Delftia tsuruhatensis Bet002, isolated from palm oil mill effluent, accumulated poly(3-hydroxyalkanoates) (PHAs) when grown on aliphatic fatty acids, sugars, and glycerol. The substrates were supplied at 20:1 C/N mole ratio. Among C-even n-alkanoic acids, myristic acid gave the highest PHA content 26 and 28 wt% in P. putida and D. tsuruhatensis, respectively. Among C-odd n-alkanoic acids, undecanoic gave the highest PHA content at 40 wt% in P. putida and 46 wt% in D. tsuruhatensis on pentadecanoic acid. Sugar and glycerol gave <10 wt% of PHA content for both bacteria. Interestingly, D. tsuruhatensis accumulated both short- and medium-chain length PHA when supplied with n-alkanoic acids ranging from octanoic to lauric, sucrose, and glycerol with 3-hydroxybutyrate as the major monomer unit. In P. putida, the major hydroxyalkanoates unit was 3-hydroxyoctanoate and 3-hydroxydecanoate when grown on C-even acids. Conversely, 3-hydroxyheptanoate, 3-hydrxoynonanoate, and 3-hydroxyundecanoate were accumulated with C-odd acids. Weight-averaged molecular weight (Mw ) was in the range of 53-81 kDa and 107-415 kDa for P. putida and D. tsuruhatensis, respectively. Calorimetric analyses indicated that both bacteria synthesized semicrystalline polymer with good thermal stability with degradation temperature (Td ) ranging from 178 to 282 °C.

Green synthesis of bacterial gold nanoparticles conjugated to resveratrol as delivery vehicles.

Bio-directed synthesis of metal nanoparticles is gaining importance in view of their biocompatibility, low toxicity and eco-friendly characteristics. The present study describes the application of resveratrol conjugated gold nanoparticles as effective delivery vehicles. The green chemistry approach was used for the synthesis of gold nanoparticles by using the culture supernatant of Delftia sp. strain KCM-006. The synthesized gold nanoparticles were mono-dispersed, spherical in shape with an average size of 11.3 nm. They were found to be photoluminescent and crystalline in nature with a zeta potential of -25 mV, indicating their high stability. Resveratrol, an anticancer drug, was conjugated to these gold nanoparticles (RSV-AuNP). The cell viability and immunocytochemistry analysis with human lung cancer cell line (A549) demonstrated that RSV-AuNPs were 65% more effective as drug when compared to resveratrol alone. In vitro observations on the drug release from these nanoparticles exhibited pH dependency; the release was significant (95%) under acidic conditions (pH 5.2) when compared to physiological conditions (pH 7.4).

Enhancement of stress tolerance in the polyhydroxyalkanoate producers without mobilization of the accumulated granules.

Poly(3-hydroxybutyrate) [P(3HB)], a polymer belonging to the polyhydroxyalkanoate (PHA) family, is accumulated by numerous bacteria as carbon and energy storage material. The mobilization of accumulated P(3HB) is associated with increased stress and starvation tolerance. However, the potential function of accumulated copolymer such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] remained unknown. In this study, Delftia acidovorans DS 17 was used to evaluate the contributions of P(3HB) and P(3HB-co-3HV) granules during simulated exogenous carbon deprivation on cell survival by transferring cells with PHAs to carbon-free mineral salt medium supplemented with 1% (w/v) nitrogen source. By mobilizing the intracellular P(3HB) and P(3HB-co-3HV) at 11 and 40 mol% 3HV compositions, the cells survived starvation. Surprisingly, D. acidovorans containing P(3HB-co-94 mol% 3HV) also survived although the mobilization was not as effective. Similarly, recombinant Escherichia coli pGEM-T::phbCAB(Cn) (harboring the PHA biosynthesis genes of Cupriavidus necator) containing P(3HB) granules had a higher viable cell counts compared to those without P(3HB) granules but without any P(3HB) mobilization when exposed to oxidative stress by photoactivated titanium dioxide. This study provided strong evidence that enhancement of stress tolerance in PHA producers can be achieved without mobilization of the previously accumulated granules. Instead, PHA biosynthesis may improve bacterial survival via multiple mechanisms.

Immobilization of Delftia tsuruhatensis in macro-porous cellulose and biodegradation of phenolic compounds in repeated batch process.

Delftia tsuruhatensis BM90, previously isolated from Tyrrhenian Sea and selected for its ability to degrade a wide array of phenolic compounds, was immobilized in chemically modified macro porous cellulose. The development of bacterial adhesion on the selected carrier was monitored by scanning electron microscopy. Evident colonization started already after 8h of incubation. After 72h, almost all the carrier surface was covered by the bacterial cells. Extracellular bacterial structures, such as pili or fimbriae, contributed to carrier colonization and cell attachment. Immobilized cells of D. tsuruhatensis were tested for their ability to biodegrade a pool of 20 phenols in repeated batch process. During the first activation batch (72h), 90% of phenols degradation was obtained already in 48h. In the subsequent batches (up to 360h), same degradation was obtained after 24h only. By contrast, free cells were slower: to obtain almost same degradation, 48h were needed. Thus, process productivity, achieved by the immobilized cells, was double than that of free cells. Specific activity was also higher suggesting that the use of immobilized D. tsuruhatensis BM90 could be considered very promising in order to obtain an efficient reusable biocatalyst for long-term treatment of phenols containing effluents.

Biodegradation of 2-chloroaniline, 3-chloroaniline, and 4-chloroaniline by a novel strain Delftia tsuruhatensis H1.

A new strain Delftia tsuruhatensis H1 able to degrade several chloroanilines (CAs) as individual compounds or a mixture was isolated from a CA-degrading mixed bacterial culture. The isolated strain could completely degrade 3-CA and 4-CA as growth substrates, while concurrently metabolize 2-CA by growing on other CA compounds. The strain could also efficiently degrade all the three CA components when presented as a mixture. Following CA consumption, stoichiometric amounts of chloride were released and small amount of soluble metabolites accumulated in the medium, indicating that the loss of CA was mainly via mineralization and incorporation into cell material. The additions of yeast extract, citrate or succinate appeared to accelerate CA degradation. In contrast, aniline strongly inhibited the CA degradation. The strain H1 could also decompose other substituted aniline compounds such as 3,4-dichloroaniline, 4-methylaniline, 2,3-dichloroaniline and 2,4-dichloroaniline. The elimination of these CA compounds seemed to occur via an ortho-cleavage pathway.

Characterization of a novel plant growth-promoting bacteria strain Delftia tsuruhatensis HR4 both as a diazotroph and a potential biocontrol agent against various plant pathogens.

A novel, plant growth-promoting bacterium Delftia tsuruhatensis, strain HR4, was isolated from the rhizoplane of rice (Oryza sativa L., cv. Yueguang) in North China. In vitro antagonistic assay showed this strain could suppress the growth of various plant pathogens effectively, especially the three main rice pathogens (Xanthomonas oryzae pv. oryzae, Rhizoctonia solani and Pyricularia oryzae Cavara). Treated with strain HR4 culture, rice blast, rice bacterial blight and rice sheath blight for cv. Yuefu and cv. Nonghu 6 were evidently controlled in the greenhouse. Strain HR4 also showed a high nitrogen-fixing activity in N-free Döbereiner culture medium. The acetylene reduction activity and 15N2-fixing activity (N2FA) were 13.06 C2H4 nmolml(-1) h(-1) and 2.052 15Na.e.%, respectively. The nif gene was located in the chromosome of this strain. Based on phenotypic, physiological, biochemical and phylogenetic studies, strain HR4 could be classified as a member of D. tsuruhatensis. However, comparisons of characteristics with other known species of the genus Delftia suggested that strain HR4 was a novel dizotrophic PGPB strain.