Effect of carbon starvation on p-nitrophenol degradation by a Moraxella strain in buffer and river water

Managing the efficiencies of three different bacterial isolates for removing atrazine from wastewater

Three individual bacterial isolates previously isolated from two types of soil with a different history of atrazine applications were chosen, purified, and subjected to subsequent work. Identification of the individual bacterial isolates was conducted using molecular methods 16S rRNA and then tested for their atrazine degradation potentials. Effects of different parameters like mixing, starvation, UV exposure, and sodium citrate for enhancing the atrazine bioremediation process by identified bacteria were also studied. The molecular method identified individual bacterial isolates as Stenotrophomonas sp. strain SD2 (strain SD2), Bacillus cereus strain BC3 (strain BC3), and Paenarthrobacter ureafaciens strain AD3 (strain AD3). The bacterial isolate strain AD3 was able to degrade 47.95% of atrazine after 28 days. Mixing strain AD3 with strain BC3 showed almost doubled of atrazine degradation percentage (61.39%) of using strain BC3 as an individual isolate (36.59%). The atrazine degradation efficacy for Stenotrophomonas sp. strain SD2, Bacillus cereus strain BC3, and Paenarthrobacter ureafaciens strain AD3 was increased between 1.28 and 4.32 folds after the starvation process. The UV exposure enhanced the efficiencies of the tested isolates either individual or mixtures (from 1.08 to 4.63-fold). Adding sodium citrate as a stimulator to the media of growing the tested isolates enhanced their potential for atrazine degradation.

Metabolic Engineering of Escherichia coli for Methyl Parathion Degradation

Organophosphate compounds are widely used in pesticides to control weeds, crop diseases, and insect pests. Unfortunately, these synthetic compounds are hazardous and toxic to all types of living organisms. In the present work, Escherichia coli was bioengineered to achieve methyl parathion (MP) degradation via the introduction of six synthetic genes, namely, opdS, pnpAS, pnpBS, pnpCS, pnpDS, and pnpES, to obtain a new transformant, BL-MP. MP and its subsequent decomposition intermediates were completely degraded by this transformant to enter the metabolites of multiple anabolic pathways. The MP-degraded strain created in this study may be a promising candidate for the bioremediation of MP and potential toxic intermediates.

Starvation-Dependent Inhibition of the Hydrocarbon Degrader Marinobacter sp. TT1 by a Chemical Dispersant

During marine oil spills, chemical dispersants are used routinely to disperse surface slicks, transferring the hydrocarbon constituents of oil into the aqueous phase. Nonetheless, a comprehensive understanding of how dispersants affect natural populations of hydrocarbon-degrading bacteria, particularly under environmentally relevant conditions, is lacking. We investigated the impacts of the dispersant Corexit EC9500A on the marine hydrocarbon degrader Marinobacter sp. TT1 when pre-adapted to either low n-hexadecane concentrations (starved culture) or high n-hexadecane concentrations (well-fed culture). The growth of previously starved cells was inhibited when exposed to the dispersant, as evidenced by 55% lower cell numbers and 30% lower n-hexadecane biodegradation efficiency compared to cells grown on n-hexadecane alone. Cultures that were well-fed did not exhibit dispersant-induced inhibition of growth or n-hexadecane degradation. In addition, fluorescence microscopy revealed amorphous cell aggregate structures when the starved culture was exposed to dispersants, suggesting that Corexit affected the biofilm formation behavior of starved cells. Our findings indicate that (previous) substrate limitation, resembling oligotrophic open ocean conditions, can impact the response and hydrocarbon-degrading activities of oil-degrading organisms when exposed to Corexit, and highlight the need for further work to better understand the implications of environmental stressors on oil biodegradation and microbial community dynamics.

Enhancing methyl parathion degradation by the immobilization of Burkholderia sp. isolated from agricultural soils

Organophosphate pesticides are of great interest for research because they are currently the most commonly used pesticides. In this study, a bacterial strain capable of completely degrading methyl parathion (MP) was isolated from agricultural soils in central Mexico. This strain was designated strain S5-2 and was identified as Burkholderia cenocepacia. To increase degradation yields, cells were immobilized on three different supports: powdered zeolite and Opuntia sp. and Agave sp. fibers. The results indicated a significant increase in MP hydrolysis and p-nitrophenol (PNP) degradation with immobilized cells compared to free cell cultures. Furthermore, immobilized cells were capable of withstanding and degrading higher concentrations of PNP compared to cell suspension cultures. The cell viability in the free cell cultures, as well as PNP degradation, was affected at concentrations greater than 25 mg/L. In contrast, cells immobilized on Opuntia sp. and Agave sp. fibers completely degraded PNP at concentrations of 100 mg/L. To verify that MP solution toxicity was decreased by B. cenocepacia strain S5-2 via pesticide degradation, we measured the acetylcholinesterase activity, both before and after treatment with bacteria. The results demonstrate that the activity of acetylcholinesterase was unaffected after MP degradation by bacteria.

Viable but non-culturable (VBNC) bacteria: Gene expression in planktonic and biofilm cells

Viable but non-culturable (VBNC) bacteria are common in nutrient poor and/or stressed environments as planktonic cells and biofilms. This article discusses approaches to researching VBNC bacteria to obtain knowledge that is lacking on their gene expression while in the VBNC state, and when they enter into and then recover from this state, when provided with the necessary nutrients and environmental conditions to support growth and cell division. Two-dimensional gel electrophoresis of proteins, global gene expression, reverse-transcription polymerase chain reaction (PCR) analysis and sequencing by synthesis coupled with data on cell numbers, viability and species present are central to understanding the VBNC state.

2,6-Dichlorobenzamide (BAM) herbicide mineralisation by Aminobacter sp. MSH1 during starvation depends on a subpopulation of intact cells maintaining vital membrane functions

Mineralisation capability was studied in the 2,6-dichlorobenzamide (BAM)-degrading Aminobacter sp. MSH1 under growth-arrested conditions. Cells were starved in mineral salts (MS) solution or groundwater before (14)C-labelled BAM (0.1mM) was added. Cell physiology was monitored with a panel of vitality stains combined with flow cytometry to differentiate intact, depolarised and dead cells. Cells starved for up to 3 weeks in MS solution showed immediate growth-linked mineralisation after BAM amendment while a lag-phase was seen after 8 weeks of starvation. In contrast, cells amended with BAM in natural groundwater showed BAM mineralisation but no growth. The cell-specific mineralisation rate was always comparable (10(-16)molCintact cell(-1)day(-1)) independent of media, growth, or starvation period after BAM amendment; lower rates were only observed as BAM concentration decreased. MSH1 seems useful for bioremediation and should be optimised to maintain an intact cell subpopulation as this seems to be the key parameter for successful mineralisation.

Novel detection of Escherichia coli beta-D-glucuronidase activity using a microbially-modified glassy carbon electrode and its potential for faecal pollution monitoring

The electrochemical detection of Escherichia coli beta-D-glucuronidase activity as a means of monitoring water pollution by faecal material was investigated using separate Moraxella- and Pseudomonas putida-modified glassy carbon electrodes. The former was more sensitive and selective. The Moraxella-modified biosensor was 100 times more rapid and sensitive than the spectrophotometric detection of beta-D-glucuronidase activity. The experimental limit of detection of the biosensor was two c.f.u. per 100 ml polluted water sample within 20 min. The biosensor gave a linear response to commercial beta-D-glucuronidase concentration between 0.2 ng and 2 microg ml(-1). The biosensor detected activity of beta-D-glucuronidase from viable but non-culturable (VBNC) cells and can therefore serve as a presence or absence device for rapid water quality monitoring.

Mineralization of paraoxon and its use as a sole C and P source by a rationally designed catabolic pathway in Pseudomonas putida

Organophosphate compounds, which are widely used as pesticides and chemical warfare agents, are cholinesterase inhibitors. These synthetic compounds are resistant to natural degradation and threaten the environment. We constructed a strain of Pseudomonas putida that can efficiently degrade a model organophosphate, paraoxon, and use it as a carbon, energy, and phosphorus source. This strain was engineered with the pnp operon from Pseudomonas sp. strain ENV2030, which encodes enzymes that transform p-nitrophenol into beta-ketoadipate, and with a synthetic operon encoding an organophosphate hydrolase (encoded by opd) from Flavobacterium sp. strain ATCC 27551, a phosphodiesterase (encoded by pde) from Delftia acidovorans, and an alkaline phosphatase (encoded by phoA) from Pseudomonas aeruginosa HN854 under control of a constitutive promoter. The engineered strain can efficiently mineralize up to 1 mM (275 mg/liter) paraoxon within 48 h, using paraoxon as the sole carbon and phosphorus source and an inoculum optical density at 600 nm of 0.03. Because the organism can utilize paraoxon as a sole carbon, energy, and phosphorus source and because one of the intermediates in the pathway (p-nitrophenol) is toxic at high concentrations, there is no need for selection pressure to maintain the heterologous pathway.

Visible laser and UV-A radiation impact on a PNP degrading Moraxella strain and its rpoS mutant

The role of stationary phase sigma factor gene (rpoS) in the stress response of Moraxella strain when exposed to radiation was determined by comparing the stress responses of the wild-type (WT) and its rpoS knockout (KO) mutant. The rpoS was turned on by starving the WT cultures for 24 h in minimal salt medium. Under non-starved condition, both WT and KO planktonic Moraxella cells showed an increase in mortality with the increase in duration of irradiation. In the planktonic non-starved Moraxella, for the power intensity tested, UV radiation caused a substantially higher mortality rate than did by the visible laser light (the mortality rate observed for 15-min laser radiation was 53.4 +/- 10.5 and 48.7 +/- 8.9 for WT and KO, respectively, and 97.6 +/- 0 and 98.5 +/- 0 for 25 s of UV irradiation in WT and KO, respectively). However, the mortality rate decreased significantly in the starved WT when exposed to these two radiations. In comparison, rpoS protected the WT against the visible laser light more effectively than it did for the UV radiation. The WT and KO strains of Moraxella formed distinctly different types of biofilms on stainless steel coupons. The KO strain formed a denser biofilm than did the WT. Visible laser light removed biofilms from the surfaces more effectively than did the UV. This was true when comparing the mortality of bacteria in the biofilms as well. The inability of UV radiation to penetrate biofilms due to greater rates of surface absorption is considered to be the major reason for the weaker removal of biofilms in comparison to that of the visible laser light. This result suggests that high power visible laser light might be an effective tool for the removal of biofilms.

Development of a microtiter plate-based method for determination of degradation profile of nitrophenolic compounds

A microtiter plate-based assay was developed for the automatic monitoring of degradation profile of the yellow-coloured nitrophenolic compounds. The method enables to reduce the intervals between measurements of substrate concentration to minutes and to overcome the problem of discontinuity of sampling typical for conventional methods. The concentrations of nitrophenolic compounds were calculated from the absorbance values determined automatically by BIOSCREEN C. Verification of the method was based on the comparison of results with the conventional HPLC method results. The values of the rate and saturation constants were comparable for both the microtiter plate-based assay and the conventional HPLC method. The automatic method described here seems to be efficient for the screening degradation studies, which requires the treatment of quantity of samples.