Juliana A. Ramsay

PHB recovery by hypochlorite digestion of non-PHB biomass

Hypochlorite digestion of bacterial biomass from intracellular poly-β-hydroxybutyrate (PHB) has not been used on a large scale since it has been reported to severely degrade PHB. In this study, to minimize degradation, the initial biomass concentration, digestion time and pH of the hypochlorite solution were optimized. Consequently, PHB of 95% purity with a weight average molecular weight (MW) of 600,000 and a polydispersity index (PI) of 4.5 was recovered from biomass initially containing PHB with a MW of 1,200,000 and a PI of 3.

Processing and characterization of thermoplastic starch/polyethylene blends

Abstract The behaviour of gelatinized starch plasticized with glycerol (also known as thermoplastic starch (TS)) is studied as the dispersed component in a polyethylene (LDPE or LLDPE) matrix. A processing technique was developed to compound the blends in one continuous process in a co-rotating twin-screw extruder fed by a single-screw extruder. The use of the single-screw as a side feeder allowed for gelatinization of the starch before feeding it into the twin-screw at controlled temperature and pressure. The screw configuration of the twin-screw extruder maintained high pressure (⩾0.9 MPa) during blending to prevent early evaporation of water. These materials displayed morphological characteristics typical of immiscible polymer-polymer blends. The number-average diameter of the dispersed phase increased from 4 μm with 8 wt% TS to 18 μm with 36 wt% TS in LDPE blends. It ranged from 3 to 8 μm in LLDPE blends containing 7 to 39 wt% TS. These results therefore indicate the possibility of achieving a level of morphological control with respect to the size and shape of the dispersed phase in these systems. Dry granular starch, on the other hand, typically is dispersed as a spherical like particle with a fixed morphology of approximately 10 μm. The blends in this study, at high TS loadings, demonstrate high elongational properties at break even without addition of an interfacial modifier. The LDPE blend containing 22% TS had 240% elongation at break and its modulus was 109 MPa. The LLDPE blend containing 39% TS had more than 540% elongation at break, while the modulus was 136 MPa.

Extraction of poly-3-hydroxybutyrate using chlorinated solvents

Recovery of poly-3-hydroxybutyrate (PHB) in three chlorinated solvents with or without acetone pretreatment and degradation of extracted PHB (99% pure) in hot chloroform were studied. When lyophilized Alcaligenes eutrophus biomass was used, the best results were obtained with acetone pretreatment and solvent reflux for 15 min in methylene chloride or chloroform. Recovered PHB had a 95% purity and molecular weights (Mw) of 1,050,000 and 930,000 g/mol respectively. Further heating resulted in a serious Mw, loss at reflux temperatures. Degradation of extracted PHB at 110°C in chloroform was due to random and chain-end scission, the former being predominant.

Effects of Mn2+ and NH+4 concentrations on laccase and manganese peroxidase production and Amaranth decoloration by Trametes versicolor

Abstract Extracellular lignin peroxidase (LiP) was not detected during decoloration of the azo dye, Amaranth, by Trametes versicolor. Approximately twice as much laccase and manganese peroxidase (MnP) was produced by decolorizing cultures compared to when no dye was added. At a low Mn2+ concentration (3 M), N-limited (1.2 mM NH4+) cultures decolorized eight successive additions of Amaranth with no visible sorption to the mycelial biomass. At higher Mn2+ concentrations (200 M), production of MnP increased and that of laccase decreased, but the rate or number of successive Amaranth decolorations was unaffected. There was always a 6-h to 8-h lag prior to decoloration of the first aliquot of Amaranth, regardless of MnP and laccase concentrations. Although nitrogen-rich (12 mM NH4+) cultures at an initial concentration of 200 M Mn2+ produced high laccase and MnP levels, only three additions of Amaranth were decolorized, and substantial mycelial sorption of the dye occurred. While the results did not preclude roles for MnP and laccase, extracellular MnP and laccase alone were insufficient for decoloration. The cell-free supernatant did not decolorize Amaranth, but the mycelial biomass separated from the whole broth and resuspended in fresh medium did. This indicates the involvement of a mycelial-bound, lignolytic enzyme or a H2O2-generating mechanism in the cell wall. Nitrogen limitation was required for the expression of this activity.

Contribution of manganese peroxidase and laccase to dye decoloration by Trametes versicolor

During dye decoloration by Trametes versicolor ATCC 20869 in modified Kirk’s medium, manganese peroxidase (MnP) and laccase were produced, but not lignin peroxidase, cellobiose dehydrogenase or manganese-independent peroxidase. Purified MnP decolorized azo dyes [amaranth, reactive black 5 (RB5) and Cibacron brilliant yellow] in Mn2+-dependent reactions but did not decolorize an anthraquinone dye [Remazol brilliant blue R (RBBR)]. However, the purified laccase decolorized RBBR five to ten times faster than the azo dyes and the addition of a redox mediator, 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid), did not alter decoloration rates. Amaranth and RB5 were decolorized the most rapidly by MnP since they have a hydroxyl group in an ortho position and a sulfonate group in the meta position relative to the azo bond. During a typical batch decoloration with the fungal culture, the ratio of laccase:MnP was 10:1 to 20:1 (based on enzyme activity) and increased to greater than 30:1 after decoloration was complete. Since MnP decolorized amaranth about 30 times more rapidly than laccase per unit of enzyme activity, MnP should have contributed more to decoloration than laccase in batch cultures.

Recovery of poly-3-hydroxyalkanoic acid granules by a surfactant-hypochlorite treatment

When Alcaligenes eutrophus biomass was treated with a surfactant and then washed with hypochlorite, the recovered poly-3-hydroxyalkanoic acid (PHA) granules were 97 to 98% pure with a molecular weight (MW) between 730,000 and 790,000, depending on the surfactant used. When treated with only surfactant, the MW was slightly higher than that obtained with the surfactant-hypochlorite treatment but the purity was 10% lower. PHA of higher purity but lower MW was obtained with just a hypochlorite treatment.

Decoloration of textile dyes by Trametes versicolor and its effect on dye toxicity

Amaranth, Tropaeolin O, Reactive Blue 15, Congo Red, and Reactive Black 5 were completely decolorized with no dye sorption by Trametes versicolor. Cibacron Brilliant Red 3G-P, Cibacron Brilliant Yellow 3B-A, and Remazol Brilliant Blue R were partially decolorized with some dye sorbed to the biomass. The Microtox assay before decoloration showed that Amaranth and Tropaeolin O were not toxic [the percent concentration to decrease 20% of the luminescence of Vibrio fischeri (EC20) was greater than 100%]; Cibacron Brilliant Yellow 3B-A, Reactive Blue 15 and Cibacron Brilliant Red 3G-P were moderately non-toxic (100% > EC20 > 75%); Remazol Brilliant Blue R was toxic (75% > EC20 > 50%); and Congo Red and Reactive Black 5 were moderately toxic (50% > EC20 > 25%). After decoloration the toxicity of the solutions containing Amaranth, Tropaeolin O and Reactive Black 5 was unchanged; Reactive Blue 15, Remazol Brilliant Blue R and Cibacron Brilliant Red 3G-P decreased to non-toxic levels; and Cibacron Brilliant Yellow 3B-A and Congo Red became very toxic (EC20 < 25%).

Fermentation process development for the production of medium-chain-length poly-3-hyroxyalkanoates

This paper presents a review of the existing fermentation processes for the production of medium-chain-length poly-3-hydroxyalkanoates (MCL-PHAs). These biodegradable polymers are usually produced most efficiently from structurally related carbon sources such as alkanes and alkanoic acids. Unlike alkanoic acids, alkanes exhibit little toxicity but their low aqueous solubility limits their use in high density culture. Alkanoic acids pose little mass transfer difficulty, but their toxicity requires that their concentration be well controlled. Using presently available technology, large-scale production of MCL-PHA from octane has been reported to cost from US

Review: microbial mechanisms of accessing insoluble Fe(III) as an energy source

5 to 10 per kilogram, with expenditures almost evenly divided between carbon source, fermentation process, and the separation process. However, MCL-PHAs, even some with functional groups in their subunits, can also be produced from cheaper unrelated carbon sources, such as glucose. Metabolic engineering and other approaches should also allow increased PHA cellular content to be achieved. These approaches, as well as a better understanding of fermentation kinetics, will likely result in increased productivity and lower production costs.

Identification of the key factors affecting composting of a weathered hydrocarbon-contaminated soil

Of all the terminal electron acceptors, Fe(III) is the most naturally abundant in many subsurface environments. Fe(III)-reducing microorganisms are phylogenetically diverse and have been isolated from a variety of sources. Unlike most electron acceptors, Fe(III) has a very low solubility and is usually present as insoluble oxides at neutral pH. The mechanisms by which microorganisms access and reduce insoluble Fe(III) are poorly understood. Initially, it was considered that microorganisms could only reduce insoluble Fe(III) through direct contact with the oxide. However, recent studies indicate that extracellular electron shuttling or Fe(III)-chelating compounds may alleviate the need for cell–oxide contact. These include microbially secreted compounds or exogenous electron shuttling agents, mainly from humic substances. Electron shuttling via humic substances is likely a significant process for Fe(III) reduction in subsurface environments. This paper reviews the various mechanisms by which Fe(III) reduction may be occurring in pure culture and in soils and sediments.