Biological degradation of plastics: a comprehensive review

Lack of degradability and the closing of landfill sites as well as growing water and land pollution problems have led to concern about plastics. With the excessive use of plastics and increasing pressure being placed on capacities available for plastic waste disposal, the need for biodegradable plastics and biodegradation of plastic wastes has assumed increasing importance in the last few years. Awareness of the waste problem and its impact on the environment has awakened new interest in the area of degradable polymers. The interest in environmental issues is growing and there are increasing demands to develop material which do not burden the environment significantly. Biodegradation is necessary for water-soluble or water-immiscible polymers because they eventually enter streams which can neither be recycled nor incinerated. It is important to consider the microbial degradation of natural and synthetic polymers in order to understand what is necessary for biodegradation and the mechanisms involved. This requires understanding of the interactions between materials and microorganisms and the biochemical changes involved. Widespread studies on the biodegradation of plastics have been carried out in order to overcome the environmental problems associated with synthetic plastic waste. This paper reviews the current research on the biodegradation of biodegradable and also the conventional synthetic plastics and also use of various techniques for the analysis of degradation in vitro.     

Proceedings of the SMBE Tri-National Young Investigators' Workshop 2005. Insight into the diversity and evolution of the cryptomonad nucleomorph genome

The cryptomonads are an enigmatic group of marine and freshwater unicellular algae that acquired their plastids through the engulfment and retention of a eukaryotic (secondary) endosymbiont. Together with the chlorarachniophyte algae, the cryptomonads are unusual in that they have retained the nucleus of their endosymbiont in a miniaturized form called a nucleomorph. The nucleomorph genome of the cryptomonad Guillardia theta has been completely sequenced and with only three chromosomes and a total size of 551 kb, is a model of nuclear genome compaction. Using this genome as a reference, we have investigated the structure and content of nucleomorph genomes in a wide range of cryptomonad algae. In this study, we have sequenced nine new cryptomonad nucleomorph 18S ribosomal DNA (rDNA) genes and four heat shock protein 90 (hsp90) gene fragments, and using pulsed-field gel electrophoresis and Southern hybridizations, have obtained nucleomorph genome size estimates for nine different species. We also used long-range polymerase chain reaction to obtain nucleomorph genomic fragments from Hanusia phi CCMP325 and Proteomonas sulcata CCMP704 that are syntenic with the subtelomeric region of nucleomorph chromosome I in G. theta. Our results indicate that (1) the presence of three chromosomes is a common feature of the nucleomorph genomes of these organisms, (2) nucleomorph genome size varies dramatically in the cryptomonads examined, (3) unidentified cryptomonad species CCMP1178 has the largest nucleomorph genome identified to date at approximately 845 kb, (4) nucleomorph genome size reductions appear to have occurred multiple times independently during cryptomonad evolution, (5) the relative positions of the 18S rDNA, ubc4, and hsp90 genes are conserved in three different cryptomonad genera, and (6) interchromosomal recombination appears to be rapidly changing the size and sequence of a repetitive subtelomeric region of the nucleomorph genome between the 18S rDNA and ubc4 loci. These results provide a glimpse into the genetic diversity of nucleomorph genomes in cryptomonads and set the stage for more comprehensive sequence-based studies in closely and distantly related taxa.     

Exencephaly and axial skeletal dysmorphogenesis induced by maternal exposure to cadmium in the mouse

To investigate the axial skeletal dysmorphogenesis associated with exencephaly and facial abnormalities, two doses of cadmium chloride (4 mg/kg and 6 mg/kg) were administered subcutaneously to MF1 mice on day 7 of gestation (sperm-positive day = day 0). Fetuses were collected on day 18. Gross examination revealed a very high incidence of cranioschisis aperta with exencephaly, maxillary and mandibular hypoplasia, low-set microtia, edema, and growth retardation of fetuses in both treatment groups. Alizarin red S-stained and cleared skeletal preparations of these embryos revealed hypoplasia of the premaxilla, maxilla, nasal bone, zygoma, and mandible of the facial skeleton. The orbital plate represented the frontal bone. The vault of the skull was conspicuously absent. In cranioschisis, the exoccipitals had splayed and fused with the atlas. The basicranial bones were hypoplastic and crowded, thus reducing the cranial cavity. The vertebral bodies were more affected than the arches. Hemivertebrae and longitudinal fusion of centra and arches were also noted. The ribs were usually rudimentary. Agenesis, fusion, and forking of ribs were frequently observed. The sternebrae were rudimentary, bipartite, or longitudinally fused. These data clearly establish the association between neural tube and axial mesodermal abnormalities and emphasize the interdependence of the neurectoderm and mesoderm in normal morphogenesis.     

Kinetics and thermodynamics of catalysis and thermal inactivation of a novel α-amylase (Tp-AmyS) from Thermotoga petrophila

Abstract

This research is focussed on kinetic, thermodynamic and thermal inactivation of a novel thermostable recombinant α-amylase (Tp-AmyS) from Thermotoga petrophila. The amylase gene was cloned in pHIS-parallel1 expression vector and overexpressed in Escherichia coli. The steady-state kinetic parameters (V_max, K_m, k_cat and k_cat/K_m) for the hydrolysis of amylose (1.39?mg/min, 0.57?mg, 148.6?s^?1, 260.7), amylopectin (2.3?mg/min, 1.09?mg, 247.1?s^?1, 226.7), soluble starch (2.67?mg/min, 2.98?mg, 284.2?s^?1, 95.4) and raw starch (2.1?mg/min, 3.6?mg, 224.7?s^?1, 61.9) were determined. The activation energy (E_a), free energy (ΔG), enthalpy (ΔH) and entropy of activation (ΔS) at 98?°C were 42.9?kJ mol^?1, 74?kJ mol^?1, 39.9?kJ mol^?1 and ?92.3 J mol^?1 K^?1, respectively, for soluble starch hydrolysis. While ΔG of substrate binding (ΔG_E-S) and ΔG of transition state binding (ΔG_E-T) were 3.38 and ?14.1?kJ mol^?1, respectively. Whereas, EaD, Gibbs free energy (ΔG*), increase in the enthalpy (ΔH*) and activation entropy (ΔS*) for activation of the unfolding of transition state were 108, 107, 105?kJ mol^?1 and ?4.1 J mol^?1 K^?1. The thermodynamics of irreversible thermal inactivation of Tp-AmyS revealed that at high temperature the process involves the aggregation of the protein.     

Description of a new species of Anuretes (Copepoda: Caligidae) from Kerala

A new species ofAnuretes collected from the gills ofDiagramma crassispinum Day at Cape Comorin, India, is described in detail. The carapace of the three females obtained was folded ventrally likeHermilius on the gill filaments.     

Description of a new species of Lepeophtheirus (copepoda: caligidae) from Kerala

A new species of Lepeophtheirus collected from Plotosus anguillaris (Bloch) by the author is described in detail. All the related species of the genus are compared with Lepeophtheirus anguilli sp. nov.     

Distribution of natural radionuclide40K in biotic and abiotic components of the Cauvery river system,Tiruchirapalli, India

Abiotic components like water and sediment, and biotic components such as mussels, fish and grass collected from Cauvery river at Tiruchirapalli were analysed for⁴⁰K activity. The highest level of⁴⁰K activity was found in the sediment (342 mBq g^-1 dry weight) and the lowest activity was found in water (2·209 mBq ml⁻¹). In the freshwater musselParreysia favidens (Benson)⁴⁰K activity was estimated in the total soft tissues and shells of mussels belonging to three different size groups. In all the size groups⁴⁰K activity was two times higher in shells (68–39 mBq g^-1 fresh weight) than in the total soft tissues (25–17 mBq g^-1 fresh weight). The results indicate that the younger mussels accumulated more⁴⁰K than the older ones. The ability of internal organs of mussels belonging to group III to accumulate⁴⁰K was in the following order: gills > digestive gland > foot > mantle. The values ranged from 47 to 18 mBq g⁻¹ fresh weight in the various organs. Concentration of⁴⁰K in the mussel was distinctly higher than in the grassEchinochloa colonum (J Koenig) (95 mBq g⁻¹ fresh weight), and the concentration of⁴⁰K in the bone of the fishCirrhina cirrhosa (Bloch) (126 mBq g⁻¹ fresh weight) was higher than to that of muscle (113 mBq g⁻¹ fresh weight)