D-Tryptophan governs biofilm formation rates and bacterial interaction in P. mendocina and S. aureus.

Biofilm genesis by Pseudomonasand Staphylococcus sp is associated with biofouling in natural settings. D-Tryptophan (D-Trp) inhibits bacterial biofilms and have been proposed for biofouling control applications. In this study, D-Trp significantly inhibited Pseudomonas mendocina and Staphylococcus aureuscell attachment (biofilm formation) rates on polystyrene96-well microtiter plates in comparison with L-Tryptophan (L-Trp) and mixtures of D-/L-Tryptophan (D-/L-Trp). Theinhibitory effect was greater on P. mendocina,where the rate of cell adherence was declined to 8.79105cells/h from8.09106cells/h (control) inP. mendocina.InS. aureusit was declined to 4.29107cells/h from 9.29107cells/h(control) at 1 mM concentration. It hindered the intracellular communication and adherence in both the strains, as con-firmed by SEM and real time PCR analysis. Addition of D-Trp to preformed biofilms also caused partial disassembly. Intraand interbacterial aggregation were decreased subsequently upon treatment with D-Trp. It repressed the genes involved incell-cell communication, which could be responsible for the diminished biofilm formation of the selected strains. HenceD-Tryptophan has proved to be an effective strategy to control biofilm and may support in the development of surfacecoating technologies.

Characterization of Aerobic Denitrifying Bacterium Pseudomonas mendocina Strain GL6 and Its Potential Application in Wastewater Treatment Plant Effluent.

To remove nitrate in wastewater treatment plant effluent, an aerobic denitrifier was newly isolated from the surface flow constructed wetland and identified as Pseudomonas mendocina strain GL6. It exhibited efficient aerobic denitrification ability, with the nitrate removal rate of 6.61 mg (N)·L-1·h-1. Sequence amplification indicated that the denitrification genes napA, nirK, norB, and nosZ were present in strain GL6. Nitrogen balance analysis revealed that approximately 74.5% of the initial nitrogen was removed as gas products. In addition, the response surface methodology experiments showed that the maximum removal of total nitrogen occurred at pH 7.76, C/N ratio of 11.2, temperature of 27.8 °C, and with shaking at 133 rpm. Furthermore, under the optimized cultivation condition, strain GL6 was added into wastewater treatment plant effluent and the removal rates of nitrate nitrogen and total nitrogen reached 95.6% and 73.6%, respectively. Thus, P. mendocina strain GL6 has high denitrification potential for deep improvement of effluent quality.

Production and recovery of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) from biodiesel liquid waste (BLW).

Polyhydroxyalkanoates (PHAs) has been paid great attention because of its useful thermoplastic properties and complete degradation in various natural environments. But, at industrial level, the successful commercialization of PHAs is limited by the high production cost due to the expensive carbon source and recovery processes. Pseudomonas mendocina PSU cultured for 72 h in mineral salts medium (MSM) containing 2% (v/v) biodiesel liquid waste (BLW) produced 79.7 wt% poly(3-hydroxybutyrate) (PHB) at 72 h. In addition, this strain produced 43.6 wt% poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with 8.6 HV mol% at 60 h when added with 0.3% sodium propionate. The synthesized intracellular PHA granules were recovered and purified by the recently reported biological method using mealworms. The weight average molecular weight (Mw ) and number average molecular weight (Mn ) of the biologically extracted PHA were higher than that from the chloroform extraction with comparable melting temperature (Tm ) and high purity. This study has successfully established a low-cost process to synthesize PHAs from BLW and subsequently confirmed the ability of mealworms to extract PHAs from various kinds of bacterial cells.

Optimization of medium composition for 3-hydroxycarboxylic acid production by Pseudomonas mendocina-biodegraded polyhydroxybutyrate.

We optimized the culture medium for 3-hydroxycarboxylic acid production by Pseudomonas mendocina DS-04-T-biodegraded polyhydroxybutyrate (PHB) using the Plackett-Burman design, steepest ascent method, and Box-Behnken design. The optimized concentrations of the constituents of the culture medium were as follows: PHB (7.57 g/L), NH4 Cl (5.0 g/L), KH2 PO4 (2.64 g/L), Na2 HPO4 ·12H2 O (12 g/L), MgSO4 ·7H2 O (0.5 g/L), and CaCl2 ·2H2 O (5 mg/L). The yield of 3-hydroxycarboxylic acid obtained using the optimized culture medium was 56.8 ± 1.64%, which was 2.5-fold higher than that obtained when the unoptimized culture medium was used.

Aerobic microbial Fe acquisition from ferrihydrite nanoparticles: effects of crystalline order, siderophores, and alginate.

This research compared the bioavailability of Fe associated with two forms of the hydrous Fe oxyhydroxide nanomineral ferrihydrite (Fh)--the smaller (1-3 nm), less ordered 2-line (2L) phase and the slightly larger, (2-6 nm) more ordered 6-line (6L) phase--to the common aerobic soil bacterium Pseudomonas mendocina ymp. P. mendocina can acquire Fe from minerals using high-affinity Fe(III) binding ligands known as siderophores and a cell-associated metalloreductase that requires direct cell-mineral contact. Wild-type (WT) P. mendocina and a siderophore(-) mutant were used to monitor siderophore -related and -independent Fe acquisition from 2L and 6L Fh. Both WT and mutant strains acquired Fe from Fh, although Fe acquisition and growth were substantially greater on the 2L phase than on the 6L phase. In the absence of bacteria, copious quantities of the biofilm exopolysaccharide alginate slightly promoted dissolution of 2L and 6L Fh. In biotic experiments, added alginate slightly enhanced growth and Fe acquisition from 6L Fh but not from 2L Fh. Recent research has led to an emerging understanding that Fe-oxide nanoparticle structure, stability, and reactivity are highly sensitive to size at the nanoscale; this research emphasizes how subtle differences in nanoparticle size-related properties can also affect bioavailability.

Characterization of Pseudomonas mendocina LR capable of removing nitrogen from various nitrogen-contaminated water samples when cultivated with Cyperus alternifolius L.

A new strain of denitrifying bacterium, Pseudomonas mendocina LR, was isolated from rhizosphere soil of aquatic plants living in a river contaminated with industrial wastewater and domestic sewage. The isolate was found to fully remove as much as 613.2 mg nitrate in 60 h under stationary culture conditions. The effects of carbon sources and nitrogen sources on nitrogen removal were investigated using a modified denitrification medium (DM). Sodium citrate was identified as the most effective source of carbon. The ability of LR to adapt to different nitrogen sources, including nitrite, indicated that LR could be used in the purification of wastewater containing different forms of nitrogen. The optimal C/N ratio was 7 for LR, and it was resistant to antibiotics Amp, Chl, Ery, and Str. Plant-microbe bioaugmentation was performed to remove nitrogen dissolved in Hoagland medium and natural wastewater. An increased rate of nitrogen removal was observed when root exudates of Cyperus alternifolius L. were added simultaneously with LR. LR was not able to survive in the natural wastewater unless root exudates from umbrella grass were added. LR cultured with umbrella grass exhibited a maximal nitrogen reduction rate of 95.9% and 97.3% in Hoagland medium and wastewater, respectively. This shows that bioaugmentation utilizing plant-microbe interactions can be an effective and exhaustive means of removing nitrogen and may be an attractive approach to nitrogen reduction in natural environments and wastewater treatment factories.

Size-dependent bioavailability of hematite (α-Fe2O3) nanoparticles to a common aerobic bacterium.

The size-dependent bioavailability of hematite (α-Fe(2)O(3)) nanoparticles to obligate aerobic Pseudomonas mendocina bacteria was examined using the natural siderophore-producing wild type strain and a siderophore(-) mutant strain. Results showed that Fe from hematite less than a few tens of nm in size appears to be considerably more bioavailable than Fe associated with larger particles. This increased bioavailability is related to the total available particle surface area, and depends in part on greater accessibility of the Fe to the chelating siderophore(s). Greater bioavailability is also related to mechanism(s) that depend on cell/nanomineral proximity, but not on siderophores. Siderophore(-) bacteria readily acquire Fe from particles <10 nm but must be in direct physical proximity to the nanomineral; the bacteria neither produce a diffusible Fe-mobilizing agent nor accumulate a reservoir of dissolved Fe in supernatant solutions. Particles <10 nm appear to be capable of penetrating the outer cell wall, offering at least one possible pathway for Fe acquisition. Other cell-surface-associated molecules and/or processes could also be important, including a cell-wall associated reducing capability. The increased bioavailability of <10 nm particles has implications for both biogeochemical Fe cycling and applications involving engineered nanoparticles, and raises new questions regarding biogenic influences on adsorbed contaminants.

Roles of siderophores, oxalate, and ascorbate in mobilization of iron from hematite by the aerobic bacterium Pseudomonas mendocina.

In aerobic, circumneutral environments, the essential element Fe occurs primarily in scarcely soluble mineral forms. We examined the independent and combined effects of a siderophore, a reductant (ascorbate), and a low-molecular-weight carboxylic acid (oxalate) on acquisition of Fe from the mineral hematite (alpha-Fe(2)O(3)) by the obligate aerobe Pseudomonas mendocina ymp. A site-directed DeltapmhA mutant that was not capable of producing functional siderophores (i.e., siderophore(-) phenotype) did not grow on hematite as the only Fe source. The concentration of an added exogenous siderophore (1 microM desferrioxamine B [DFO-B]) needed to restore wild-type (WT)-like growth kinetics to the siderophore(-) strain was approximately 50-fold less than the concentration of the siderophore secreted by the WT organism grown under the same conditions. The roles of a reductant (ascorbate) and a simple carboxylic acid (oxalate) in the Fe acquisition process were examined in the presence and absence of the siderophore. Addition of ascorbate (50 microM) alone restored the growth of the siderophore(-) culture to the WT levels. A higher concentration of oxalate (100 microM) had little effect on the growth of a siderophore(-) culture; however, addition of 0.1 muM DFO-B and 100 muM oxalate restored the growth of the mutant to WT levels when the oxalate was prereacted with the hematite, demonstrating that a metabolizing culture benefits from a synergistic effect of DFO-B and oxalate.

Differential effects of Pseudomonas mendocina and Glomus intraradices on lettuce plants physiological response and aquaporin PIP2 gene expression under elevated atmospheric CO2 and drought.

Arbuscular mycorrhizal (AM) symbiosis and plant-growth-promoting rhizobacterium (PGPR) can alleviate the effects of water stress in plants, but it is unknown whether these benefits can be maintained at elevated CO2. Therefore, we carried out a study where seedlings of Lactuca sativa were inoculated with the AM fungus (AMF) Glomus intraradices N.C. Schenk & G.S. Sm. or the PGPR Pseudomonas mendocina Palleroni and subjected to two levels of watering and two levels of atmospheric CO2 to ascertain their effects on plant physiological parameters and gene expression of one PIP aquaporin in roots. The inoculation with PGPR produced the greatest growth in lettuce plants under all assayed treatments as well as the highest foliar potassium concentration and leaf relative water content under elevated [CO2] and drought. However, under such conditions, the PIP2 gene expression remained almost unchanged. G. intraradices increased significantly the AMF colonization, foliar phosphorus concentration and leaf relative water content in plants grown under drought and elevated [CO2]. Under drought and elevated [CO2], the plants inoculated with G. intraradices showed enhanced expression of the PIP2 gene as compared to P. mendocina or control plants. Our results suggest that both microbial inoculation treatments could help to alleviate drought at elevated [CO2]. However, the PIP2 gene expression was increased only by the AMF but not by the PGPR under these conditions.

Effect of exogenous reductant on growth and iron mobilization from ferrihydrite by the Pseudomonas mendocina ymp strain.

Growth of the Pseudomonas mendocina ymp strain on insoluble ferrihydrite is enhanced by exogenous reductants with concurrent increase in soluble iron concentrations. This shows that exogenous reductants play a substantial role in the overall microbial iron bioavailability. The exogenous reductants may work together with the siderophores, Fe-scavenging agents, to facilitate ferrihydrite dissolution.

Factors affecting the biodegradation of PCP by Pseudomonas mendocina NSYSU.

A pentachlorophenol (PCP) degrading bacterium was isolated from PCP-contaminated soils and identified as Pseudomonas mendocina NSYSU (P. mendocina NSYSU). The main objectives of this study were to (1) clarify the factors affecting the ability and efficiency of PCP biodegradation by P. mendocina NSYSU, and (2) optimize the use of this bacterium in bioremediation of PCP. Microcosm experiments were conducted to fulfill the objectives. In batch cultures, P. mendocina NSYSU used PCP as its sole source of carbon and energy and was capable of completely degrading this compound. This was confirmed by the stoichiometric release of chloride ion. Moreover, P. mendocina NSYSU was able to mineralize a high concentration of PCP (150 mg/L). Results from the oxygen concentration experiment reveal that the growth of P. mendocina NSYSU was inhibited under low oxygen and anaerobic conditions. Results indicate that the optimal growth conditions for P. mendocina NSYSU include the following: slightly acidic (6

Cometabolism of methyl tertiary butyl ether and gaseous n-alkanes by Pseudomonas mendocina KR-1 grown on C5 to C8 n-alkanes.

Pseudomonas mendocina KR-1 grew well on toluene, n-alkanes (C5 to C8), and 1 degrees alcohols (C2 to C8) but not on other aromatics, gaseous n-alkanes (C1 to C4), isoalkanes (C4 to C6), 2 degrees alcohols (C3 to C8), methyl tertiary butyl ether (MTBE), or tertiary butyl alcohol (TBA). Cells grown under carbon-limited conditions on n-alkanes in the presence of MTBE (42 micromoles) oxidized up to 94% of the added MTBE to TBA. Less than 3% of the added MTBE was oxidized to TBA when cells were grown on either 1 degrees alcohols, toluene, or dextrose in the presence of MTBE. Concentrated n-pentane-grown cells oxidized MTBE to TBA without a lag phase and without generating tertiary butyl formate (TBF) as an intermediate. Neither TBF nor TBA was consumed by n-pentane-grown cells, while formaldehyde, the expected C1 product of MTBE dealkylation, was rapidly consumed. Similar Ks values for MTBE were observed for cells grown on C5 to C8 n-alkanes (12.95 +/- 2.04 mM), suggesting that the same enzyme oxidizes MTBE in cells grown on each n-alkane. All growth-supporting n-alkanes (C5 to C8) inhibited MTBE oxidation by resting n-pentane-grown cells. Propane (Ki = 53 micromoles) and n-butane (Ki = 16 micromoles) also inhibited MTBE oxidation, and both gases were also consumed by cells during growth on n-pentane. Cultures grown on C5 to C8 n-alkanes also exhibited up to twofold-higher levels of growth in the presence of propane or n-butane, whereas no growth stimulation was observed with methane, ethane, MTBE, TBA, or formaldehyde. The results are discussed in terms of their impacts on our understanding of MTBE biodegradation and cometabolism.