Check out our New Publishers' Select for Free Articles

Applied Microbiology and Biotechnology (v.81, #3)

The white-rot fungus Phanerochaete chrysosporium: conditions for the production of lignin-degrading enzymes by Deepak Singh; Shulin Chen (pp. 399-417).

Investigating optimal conditions for lignin-degrading peroxidases production by Phanerochaete chrysosporium (P. chrysosporium) has been a topic for numerous researches. The capability of P. chrysosporium for producing lignin peroxidases (LiPs) and manganese peroxidases (MnPs) makes it a model organism of lignin-degrading enzymes production. Focusing on compiling and identifying the factors that affect LiP and MnP production by P. chrysosporium, this critical review summarized the main findings of about 200 related research articles. The major difficulty in using this organism for enzyme production is the instability of its productivity. This is largely due to the poor understanding of the regulatory mechanisms of P. chrysosporium responding to different nutrient sources in the culture medium, such as metal elements, detergents, lignin materials, etc. In addition to presenting the major conclusions and gaps of the current knowledge on lignin-degrading peroxidases production by P. chrysosporium, this review has also suggested further work, such as correlating the overexpression of the intra and extracellular proteins to the nutrients and other culture conditions to discover the regulatory cascade in the lignin-degrading peroxidases production process, which may contribute to the creation of improved P. chrysosporium strains leading to stable enzyme production.

Keywords: Phanerochaete chrysosporium; Lignin peroxidase; Manganese peroxidase; Culture conditions

Prospects of using marine actinobacteria as probiotics in aquaculture by Surajit Das; Louise R. Ward; Chris Burke (pp. 419-429).

Chemotherapeutic agents have been banned for disease management in aquaculture systems due to the emergence of antibiotic resistance gene and enduring residual effects in the environments. Instead, microbial interventions in sustainable aquaculture have been proposed, and among them, the most popular and practical approach is the use of probiotics. A range of microorganisms have been used so far as probiotics, which include Gram-negative and Gram-positive bacteria, yeast, bacteriophages, and unicellular algae. The results are satisfactory and promising; however, to combat the latest infectious diseases, the search for a new strain for probiotics is essential. Marine actinobacteria were designated as the chemical factory a long time ago, and quite a large number of chemical substances have been isolated to date. The potent actinobacterial genera are Streptomyces; Micromonospora; and a novel, recently described genus, Salinispora. Despite the existence of all the significant features of a good probiont, actinobacteria have been hardly used as probiotics in aquaculture. However, this group of bacteria promises to supply the most potential probiotic strains in the future.

Keywords: Aquaculture; Actinobacteria ; Streptomyces ; Probiotics; Growth; Survival

Influence of processing parameters on disintegration of Chlorella cells in various types of homogenizers by J. Doucha; K. Lívanský (pp. 431-440).

The following bead mills used for disruption of the microalga Chlorella cells were tested: (1) Dyno-Mill ECM-Pilot, grinding chamber volume 1.5 L; KDL-Pilot A, chamber volume 1.4 L; KD 20 S, chamber volume 18.3 L; KD 25 S, chamber volume 26 L of Willy A. Bachofen, Basel, Switzerland, (2) LabStar LS 1, chamber volume 0.6 L of Netzsch, Selb, Germany, (3) MS 18, chamber volume 1.1 L of FrymaKoruma, Neuenburg, Germany. Amount of disrupted cells decreased with increasing Chlorella suspension feed rate and increased up to about 85% of the beads volume in the grinding chamber of the homogenizers. It also increased with agitator speed and number of passes of the algae suspension through the chamber. The optimum beads diameter was 0.3–0.5 mm in the homogenizers Dyno-Mill and LabStar LS 1 and 0.5–0.7 mm in the homogenizer MS 18. While the degree of the cell disruption decreased with increasing cell density in Dyno-Mill and LabStar, the cell disruption in the MS 18 increased. Depending on processing parameters, more than 90% of algae cells were disrupted by passing through the bead mills and bacteria count in algae suspension was reduced to about two orders.

Keywords: Processing parameters; Disintegration efficiency; Chlorella ; Bacteria reduction

Optimization of the production of rhamnolipids by Pseudomonas aeruginosa UFPEDA 614 in solid-state culture by Doumit Camilios Neto; Joel Alexandre Meira; Janete Magali de Araújo; David Alexander Mitchell; Nadia Krieger (pp. 441-448).

In recent years, biosurfactants have attracted attention because of their low toxicity, high biodegradability, and good ecological acceptability. However, their production in submerged liquid culture is hampered by the severe foaming that occurs. Solid-state cultivation can avoid this problem. In the current work, we optimized the production of a rhamnolipid biosurfactant by Pseudomonas aeruginosa UFPEDA 614, grown on a solid medium impregnated with a solution containing glycerol. During the study, we increased the production of the biosurfactant over tenfold, with levels reaching 172 g of rhamnolipid per kilogram of dry initial substrate after 12 days. On the basis of the volume of impregnating solution added to the solid support, this yield is of the order of 46 g/L, which is comparable with the best results that have been obtained to date in submerged liquid cultivation. Our results suggest that there is a great potential for using solid-state cultivation for the production of rhamnolipids.

Keywords: Rhamnolipids; Biosurfactants; Solid-state cultivation; Solid-state fermentation; Pseudomonas aeruginosa

Impact on disinfection efficiency of cell load and of planktonic/adherent/detached state: case of Hafnia alvei inactivation by Plasma Activated Water by Georges Kamgang-Youbi; Jean-Marie Herry; Jean-Louis Brisset; Marie-Noëlle Bellon-Fontaine; Avaly Doubla; Murielle Naïtali (pp. 449-457).

This paper describes the effects of initial microbial concentration and planktonic/adherent/detached states on the efficiency of plasma-activated water. This disinfecting solution was obtained by treating distilled water with an atmospheric pressure plasma produced by gliding electric discharges in humid air. The inactivation kinetics of planktonic cells of Hafnia alvei (selected as a bacterial model) were found to be of the first order. They were influenced by the initial microbial concentration. Efficiency decreased when the initial viable population N ₀ increased, and the inactivation rate k _max was linearly modified as a function of Log₁₀ (N ₀). This relation was used to compare planktonic, adherent, and detached cells independently from the level of population. Bacteria adhering to stainless steel and high-density polyethylene were also sensitive to treatment, but at a lower rate than their free-living counterparts. Moreover, cells detached from these solid substrates exhibited an inactivation rate lower than that of planktonic cells but similar to adherent bacteria. This strongly suggests the induction of a physiological modification to bacteria during the adhesion step, rendering adherent—and further detached—bacteria less susceptible to the treatment, when compared to planktonic bacteria.

Keywords: Plasma-activated water (PAW); Glidarc; Non-thermal plasma; Initial cell load; Sessile bacteria; Released bacteria; Disinfection

An efficient succinic acid production process in a metabolically engineered Corynebacterium glutamicum strain by Shohei Okino; Ryoji Noburyu; Masako Suda; Toru Jojima; Masayuki Inui; Hideaki Yukawa (pp. 459-464).

A Corynebacterium glutamicum strain (ΔldhA-pCRA717) that overexpresses the pyc gene encoding pyruvate carboxylase while simultaneously exhibiting a disrupted ldhA gene encoding l-lactate dehydrogenase was investigated in detail for succinic acid production. Succinic acid was shown to be efficiently produced at high-cell density under oxygen deprivation with intermittent addition of sodium bicarbonate and glucose. Succinic acid concentration reached 1.24 M (146 g l⁻¹) within 46 h. The yields of succinic acid and acetic acid from glucose were 1.40 mol mol⁻¹ (0.92 g g⁻¹) and 0.29 mol mol⁻¹ (0.10 g g⁻¹), respectively. The succinic acid production rate and yield depended on medium bicarbonate concentration rather than glucose concentration. Consumption of bicarbonate accompanied with succinic acid production implied that added bicarbonate was used for succinic acid synthesis.

Keywords: Succinic acid; Corynebacterium glutamicum ; Pyruvate carboxylase

Directed evolution of a Baeyer–Villiger monooxygenase to enhance enantioselectivity by Anett Kirschner; Uwe T. Bornscheuer (pp. 465-472).

The Baeyer–Villiger monooxygenase (BVMO) BmoF1 from Pseudomonas fluorescens DSM 50106 was shown before to enantioselectively oxidize different 4-hydroxy-2-ketones to the corresponding hydroxyalkyl acetates, being the first example of a BVMO-catalyzed kinetic resolution of aliphatic acyclic ketones. However, the wild-type enzyme exhibited only moderate E values (E ∼ 55). Thus, the enantioselectivity was enhanced by means of directed evolution and optimization of reaction conditions since it was found that higher E values (E ∼ 70 for wild-type BmoF1) could already be obtained when performing biotransformations in shake flasks rather than small tubes. In a first step, random mutations were introduced by error-prone polymerase chain reaction, and BmoF1 mutants (>3,500 clones) were screened for improved activity and enantioselectivity using a microtiter-plate-based screening method. Mutations S136L and L252Q were found to increase conversion compared to wild type, while several mutations (H51L, F225Y, S305C, and E308V) were identified enhancing the enantioselectivity to a varying extent (E ∼ 75–90). In a second step, beneficial mutations were recombined by consecutive cycles of QuikChange® site-directed mutagenesis resulting in a double mutant (H51L/S136L) showing both improved conversion and enantioselectivity (E ∼ 86).

Keywords: Baeyer–Villiger monooxygenase; Directed evolution; Enzyme catalysis; Enantioselectivity; β-hydroxyketones

Involvement of PEG-carboxylate dehydrogenase and glutathione S-transferase in PEG metabolism by Sphingopyxis macrogoltabida strain 103 by Peechapack Somyoonsap; Akio Tani; Jittima Charoenpanich; Toshiyuki Minami; Kazuhide Kimbara; Fusako Kawai (pp. 473-484).

Sphingopyxis terrae and the Sphingopyxis macrogoltabida strains 103 and 203 are able to degrade polyethylene glycol (PEG). They possess the peg operon, which is responsible for the conversion of PEG to PEG-carboxylate-coenzyme A (CoA). The upstream (3.0 kb) and downstream (6.5 kb) regions of the operon in strain 103 were cloned and sequenced. The structure was well conserved between S. macrogoltabida strain 203 and S. terrae, except that two sets of transposases are absent in strain 203. The downstream region contains the genes for PEG-carboxylate dehydrogenase (PCDH), glutathione S-transferase (GST), tautomerase, and a hypothetical protein. The genes for pcdh and gst were transcribed constitutively and monocistronically, indicating that their transcription is independent of the operon regulation. PCDH and GST were expressed in Escherichia coli and characterized biochemically. PCDH is a homotetramer of 64-kDa subunits and contains one molecule of flavin adenine dinucleotide per subunit. The enzyme dehydrogenates PEG-carboxylate to yield glyoxylate, suggesting that the enzyme is the third enzyme involved in PEG degradation. GST is a homodimer of 28-kDa subunits. GST activity was noncompetitively inhibited by acyl-CoA and PEG-carboxylate-CoA, suggesting the interaction of GST with them. The proposed role for GST is to buffer the toxicity of PEG-carboxylate-CoA.

Keywords: Polyethylene glycol (PEG); peg operon; PEG-carboxylate dehydrogenase; Glutathione S-transferase; Sphingopyxis macrogoltabida

Thermotoga maritima TM0298 is a highly thermostable mannitol dehydrogenase by Seung Hoon Song; Nitasha Ahluwalia; Yvonne Leduc; Louis T. J. Delbaere; Claire Vieille (pp. 485-495).

Thermotoga maritima TM0298 is annotated as an alcohol dehydrogenase, yet it shows high identity and similarity to mesophilic mannitol dehydrogenases. To investigate this enzyme further, its gene was cloned and expressed in Escherichia coli. The purified recombinant enzyme was most active on fructose and mannitol, making it the first known hyperthermophilic mannitol dehydrogenase. T. maritima mannitol dehydrogenase (TmMtDH) is optimally active between 90 and 100 °C and retains 63% of its activity at 120 °C but shows no detectable activity at room temperature. Its kinetic inactivation follows a first-order mechanism, with half-lives of 57 min at 80 °C and 6 min at 95 °C. Although TmMtDH has a higher V _max with NADPH than with NADH, its catalytic efficiency is 2.2 times higher with NADH than with NADPH and 33 times higher with NAD⁺ than with NADP⁺. This cofactor specificity can be explained by the high density of negatively charged residues (Glu193, Asp195, and Glu196) downstream of the NAD(P) interaction site, the glycine motif. We demonstrate that TmMtDH contains a single catalytic zinc per subunit. Finally, we provide the first proof of concept that mannitol can be produced directly from glucose in a two-step enzymatic process, using a Thermotoga neapolitana xylose isomerase mutant and TmMtDH at 60 °C.

Keywords: Thermotoga maritima ; Mannitol dehydrogenase; Thermostable enzyme; Mannitol; Glucose; Fructose

Functional analysis of a fatty acid elongase from arachidonic acid-producing Mortierella alpina 1S-4 by Eiji Sakuradani; Shoichi Murata; Hiroyuki Kanamaru; Sakayu Shimizu (pp. 497-503).

We describe the isolation and characterization of a gene (MAELO) that encodes a fatty acid elongase from arachidonic acid-producing fungus Mortierella alpina 1S-4. Although the homologous MAELO gene had already been isolated from M. alpina ATCC 32221, its function had not yet been identified. The MAELO gene from M. alpina 1S-4 was confirmed to encode a fatty acid elongase by its expression in yeast Saccharomyces cerevisiae. Analysis of the fatty acid composition of the yeast transformant revealed the accumulation of 22-, 24-, and 26-carbon saturated fatty acids. On the other hand, RNA interference of the MAELO gene in M. alpina 1S-4 was carried out. The gene-silenced strain obtained on RNA interference exhibited low contents of 20-, 22-, and 24-carbon saturated fatty acids and a high content of stearic acid (18 carbons), compared with those in the wild strain. The enzyme encoded by the MAELO gene was demonstrated to be involved in the biosynthesis of 20-, 22-, and 24-carbon saturated fatty acids in M. alpina 1S-4.

Keywords: Fatty acid elongase; Mortierella ; RNA interference; Gene expression; Functional analysis

Transcriptional regulation of Corynebacterium glutamicum methionine biosynthesis genes in response to methionine supplementation under oxygen deprivation by Masako Suda; Haruhiko Teramoto; Takashi Imamiya; Masayuki Inui; Hideaki Yukawa (pp. 505-513).

Expression at the mRNA level of six methionine biosynthesis genes in Corynebacterium glutamicum cells under oxygen-deprived conditions was repressed by supplementation of medium with methionine. The repression was not observed in a mutant deficient in the TetR-type transcriptional repressor McbR. Analysis of transcriptional start sites of the methionine biosynthesis genes confirmed that McbR binding motifs exist in the promoter regions of all genes repressed by methionine supplementation. Furthermore, electrophoretic mobility shift assays revealed that not only S-adenosylhomocysteine but also S-adenosylmethionine affects binding of McbR to the promoter region of metY, suggesting that both of these methionine metabolites are involved in the regulation of methionine biosynthesis genes.

Keywords: Corynebacterium glutamicum ; Methionine biosynthesis genes; S-adenosylmethionine; McbR

Insecticidal evaluation of Beauveria bassiana engineered to express a scorpion neurotoxin and a cuticle degrading protease by Dingding Lu; Monica Pava-Ripoll; Zengzhi Li; Chengshu Wang (pp. 515-522).

To improve the insecticidal efficacy of the entomopathogen Beauveria bassiana, the fungus was genetically modified with an insect-specific scorpion neurotoxin AAIT and an insect cuticle degrading protease PR1A from another insect pathogen (Metarhizium anisopliae). The wild-type and the transformants were bioassayed against the larvae of Masson’s pine caterpillar Dendrolimus punctatus and the wax moth Galleria mellonella. In comparison to the wild-type strain, engineered isolates took fewer spores to kill 50% of pine caterpillars, 15-fold less for the aaIT single transformant Bb13T and eightfold less for the double transformant Bb13TPR1A, respectively. The median lethal times for Bb13T and Bb13TPR1A were reduced by 40% and 36.7%, respectively against D. punctatus and 24.4% and 20.9%, respectively against G. mellonella. Our data showed that the cotransformation of these two genes produced no synergistic effects on virulence improvement. It is evident from this study that AAIT could be degraded by the protease PR1A when they are expressed together, emphasizing that protein interactions need to be evaluated when working with multiple genes, particularly if they include proteases.

Keywords: Beauveria bassiana ; Genetic engineering; Scorpion neurotoxin; Protease; Virulence

Overproduction of soluble recombinant transglutaminase from Streptomyces netropsis in Escherichia coli by Yu-Jen Yu; Shih-Cheng Wu; Hung-Hsiang Chan; Yu-Cheng Chen; Zong-Yu Chen; Ming-Te Yang (pp. 523-532).

A novel microbial transglutaminase (TGase) from the cultural filtrate of Streptomyces netropsis BCRC 12429 (Sn) was purified. The specific activity of the purified TGase was 18.2 U/mg protein with an estimated molecular mass of 38 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis. The TGase gene of S. netropsis was cloned and an open reading frame of 1,242 bp encoding a protein of 413 amino acids was identified. The Sn TGase was synthesized as a precursor protein with a preproregion of 82 amino acid residues. The deduced amino acid sequence of the mature S. netropsis TGase shares 78.9–89.6% identities with TGases from Streptomyces spp. A high level of soluble Sn TGase with its N-terminal propeptide fused with thioredoxin was expressed in E. coli. A simple and efficient process was applied to convert the purified recombinant protein into an active enzyme and showed activity equivalent to the authentic mature TGase.

Keywords: Cloning; Fusion protein; Microbial transglutaminase; Proregion; Streptomyces netropsis ; Thioredoxin

Studies on the production of conjugated linoleic acid from linoleic and vaccenic acids by mixed rumen protozoa by Mamun M. Or-Rashid; Ousama AlZahal; Brian W. McBride (pp. 533-541).

The present study was designed to investigate the capability of mixed rumen protozoa to synthesize conjugated linoleic acid (CLA) from linoleic (LA) and vaccenic acids (VA). Rumen contents were collected from fistulated cows. The protozoal fraction was separated and washed several times with MB9 buffer and then resuspended in autoclaved rumen fluid. The suspensions were anaerobically incubated up to 18 h at 38.5 °C with substrates in the presence (P-AB) or the absence of antibacterial-agents (P-No-AB). Neither P-AB nor P-No-AB suspensions were capable of producing CLA from VA (11t-18:1). Linoleic acid was catabolized by P-No-AB to a greater extent than P-AB. Different isomers of CLA were synthesized by P-AB from LA. The 9c11t-CLA was predominant. Thirty seven percent of the maximum accumulated 9c11t-CLA was found in the P-AB suspension as early as 0.1 h into the incubation period. Accumulation of 10t12c-CLA in P-AB suspension was approximately 10.0 times lower than that of 9c11t-CLA. There were no significant productions of VA, 10t-18:1, and 18:0 in P-AB compared with the control, indicating that rumen protozoa have no ability to biohydrogenate CLA isomers. On the other hand, the concentrations of 10t-18:1, VA, and 18:0 in P-No-AB were greater (P < 0.05) compared with those in P-AB, indicating the role of symbiotic bacteria associated with P-No-AB in biohydrogenating CLA isomers. We concluded that mixed rumen protozoa are capable of synthesizing CLA from LA through isomerization reactions. However, they are incapable of metabolizing CLA further. They are also incapable of vaccenic acid biohydrogenation and/or desaturation.

Keywords: CLA; Rumen protozoa; Linoleic acid; Vaccenic acid

Effects of spaceflight on polysaccharides of Saccharomyces cerevisiae cell wall by Hong-Zhi Liu; Qiang Wang; Xiao-Yong Liu; Sze-Sze Tan (pp. 543-550).

Freeze-dried samples of four Saccharomyces cerevisiae strains, namely, FL01, FL03, 2.0016, and 2.1424, were subjected to spaceflight. After the satellite’s landing on Earth, the samples were recovered and changes in yeast cell wall were analyzed. Spaceflight strains of all S. cerevisiae strains showed significant changes in cell wall thickness (P < 0.05). One mutant of S. cerevisiae 2.0016 with increased biomass, cell wall thickness, and cell wall glucan was isolated (P < 0.05). The spaceflight mutant of S. cerevisiae 2.0016 showed 46.7%, 62.6%, and 146.0% increment in biomass, cell wall thickness and β-glucan content, respectively, when compared to the ground strain. Moreover, growth curve analysis showed spaceflight S. cerevisiae 2.0016 had a faster growth rate, shorter lag phase periods, higher final biomass, and higher content of β-glucan. Genetic stability analysis showed that prolonged subculturing of spaceflight strain S. cerevisiae 2.0016 did not lead to the appearance of variants, indicating that the genetic stability of S. cerevisiae 2.0016 mutant could be sufficient for its exploitation of β-glucan production.

Keywords: Spaceflight; Saccharomyces cerevisiae ; Cell wall; β-Glucan; Mannan

A mutation upstream of an ATPase gene significantly increases magnetosome production in Magnetospirillum gryphiswaldense by Jiangning Liu; Yao Ding; Wei Jiang; Jiesheng Tian; Ying Li; Jilun Li (pp. 551-558).

A mutant of Magnetospirillum gryphiswaldense, NPHB, was obtained from a conjugation experiment. An aberrant recombination occurred between a putative elongation factor-G gene (fus-like) of the bacterial chromosome and the chloramphenicol resistant gene (cat) of a suicide vector, pSUP202. Complementary experiments and transcription analysis of genes around the recombinant site showed that the cat promoter enhanced the expression of adenosine triphosphatase gene downstream. Adenosine triphosphate hydrolyzing activity in NPHB was 35% higher than in the wild-type strain (M. gryphiswaldense MSR-1). NPHB accumulated 71% less poly-β-hydroxybutyrate and consumed 56% more oxygen and 40% more lactate than MSR-1. The magnetosome content of NPHB was 69% higher than MSR-1 in flask culture. NPHB cultured in a 7.5-L bioreactor gave a maximum yield of 58.4 ± 6.4 mg magnetosomes per liter.

Keywords: Magnetospirillum gryphiswaldense ; PHB production; ATPase activity; Magnetosome production; Oxygen consumption

Dynamic analysis of Lactobacillus delbrueckii subsp. bulgaricus CFL1 physiological characteristics during fermentation by Aline Rault; Marielle Bouix; Catherine Béal (pp. 559-570).

This study aimed at examining and comparing the relevance of various methods in order to discriminate different cellular states of Lactobacillus bulgaricus CFL1 and to improve knowledge on the dynamics of the cellular physiological state during growth and acidification. By using four fluorescent probes combined with multiparametric flow cytometry, membrane integrity, intracellular esterase activity, cellular vitality, membrane depolarization, and intracellular pH were quantified throughout fermentations. Results were compared and correlated with measurements of cultivability, acidification activity (Cinac system), and cellular ability to recover growth in fresh medium (Bioscreen system). The Cinac system and flow cytometry were relevant to distinguish different physiological states throughout growth. Lb. bulgaricus cells maintained their high viability, energetic state, membrane potential, and pH gradient in the late stationary phase, despite the gradual decrease of both cultivability and acidification activity. Viability and membrane integrity were maintained during acidification, at the expense of their cultivability and acidification activity. Finally, this study demonstrated that the physiological state during fermentation was strongly affected by intracellular pH and the pH gradient. The critical pHi of Lb. bulgaricus CFL1 was found to be equal to pH 5.8. Through linear relationships between dpH and cultivability and pHi and acidification activity, pHi and dpH well described the time course of metabolic activity, cultivability, and viability in a single analysis.

Keywords: Lactic acid bacteria; Physiological state; Viability; Acidification activity; Flow cytometry

Bioremediation of trace cobalt from simulated spent decontamination solutions of nuclear power reactors using E. coli expressing NiCoT genes by G. Raghu; V. Balaji; G. Venkateswaran; A. Rodrigue; P. Maruthi Mohan (pp. 571-578).

Removal of radioactive cobalt at trace levels (≈nM) in the presence of large excess (10⁶-fold) of corrosion product ions of complexed Fe, Cr, and Ni in spent chemical decontamination formulations (simulated effluent) of nuclear reactors is currently done by using synthetic organic ion exchangers. A large volume of solid waste is generated due to the nonspecific nature of ion sorption. Our earlier work using various fungi and bacteria, with the aim of nuclear waste volume reduction, realized up to 30% of Co removal with specific capacities calculated up to 1 μg/g in 6–24 h. In the present study using engineered Escherichia coli expressing NiCoT genes from Rhodopseudomonas palustris CGA009 (RP) and Novosphingobium aromaticivorans F-199 (NA), we report a significant increase in the specific capacity for Co removal (12 μg/g) in 1-h exposure to simulated effluent. About 85% of Co removal was achieved in a two-cycle treatment with the cloned bacteria. Expression of NiCoT genes in the E. coli knockout mutant of NiCoT efflux gene (rcnA) was more efficient as compared to expression in wild-type E. coli MC4100, JM109 and BL21 (DE3) hosts. The viability of the E. coli strains in the formulation as well as at different doses of gamma rays exposure and the effect of gamma dose on their cobalt removal capacity are determined. The potential application scheme of the above process of bioremediation of cobalt from nuclear power reactor chemical decontamination effluents is discussed.

Keywords: Bioremediation; Decontamination solution; NiCoT genes; Cobalt removal; Nuclear power reactors

Comparative study of using different materials as bacterial carriers to treat hydrogen sulfide by Zhiling Li; Tonghua Sun; Nanwen Zhu; Xinde Cao; Jinping Jia (pp. 579-588).

The use of support media for the immobilization of microorganisms is widely known to provide a surface for microbial growth and protect the microorganisms from inhibitory compounds. In this study, molecular sieve, granular porous carbon, and ferric oxide desulfurizer, immobilized with autotrophic bacteria capable of oxidizing ferrous iron to ferric iron, were developed to treat hydrogen sulfide (H₂S). Their corresponding bioreactors were referred to as BMS, BPC, and BFO, respectively. H₂S loading, gas retention time, hydrogen ion, and aluminous, ferric, and ferrous iron concentrations of recycling effluents were evaluated. Thermogravimetric analysis, Brauner-Emmett-Teller method, and scanning electron microscopy were used to characterize packing materials. Results showed that the elimination capacity was in the order of BFO > BPC > BMS. This study suggested that the material characteristics progressively influenced the deodorization capacities of bioreactors. H₂S was oxidized into elemental sulfur and oxidized sulfur species, according to differences of carriers. Furthermore, this study revealed the potential application of simultaneously treating of H₂S under extremely acidic conditions.

Keywords: Biotrickling filter; Hydrogen sulfide; Molecular sieve; Porous carbon; Ferric oxide desulfurizer; Autotrophic bacteria

Prospects of using marine actinobacteria as probiotics in aquaculture by Surajit Das; Louise R. Ward; Chris Burke (pp. 589-589).

Sections

Personal tools

Applied Microbiology and Biotechnology (v.81, #3)

Sections

Personal tools

Local resources

Applied Microbiology and Biotechnology (v.81, #3)