Metabolic engineering of the model photoautotrophic cyanobacterium synechocystis for ethanol production: optimization strategies and challenges

peer-reviewedPhotoautotrophic ethanol production using model cyanobacteria is an attractive technology that offers potential for sustainable ethanol production as a biofuel. Model strains of Synechocystis PCC6803 have been metabolically engineered to convert central metabolic intermediates such as pyruvate to acetaldehyde via cloned heterologous pyruvate decarboxylase and from acetaldehyde to ethanol via cloned homologous or heterologous alcohol dehydrogenase. While the technology is now proven, strategies are required to increase the ethanol levels through metabolic and genetic engineering and in addition, production and process strategies are required to make the process sustainable. Here we discuss both genetic and molecular strategies in combination with do wnstream strategies that are being applied while also discussing challenges to future application

The Potential of the Photoautotroph Synechocystis for Metal Bioremediation

The photoautotrophic cyanobacterium Synechocystis PCC6803 has received much attention as a model photosynthetic cell factory for the production of a range of important biotech products. The biomass remaining from this activity may then have further utility in processes such as metal bioremediation. In addition Synechocystis being an inhabitant of many natural aquatic environments is seen as an environmentally friendly alternative to using chemical precipitation methodologies for metal remediation. Synechocystis produces a range of extracellular polysaccharide substances (EPS) that can undergo modification as a function of culture age and growth nutrients which have been implicated in metal biosorption. Many studies have demonstrated that high levels of charged groups present in EPS are important in forming polymeric matrices with metallic ions allowing their biosorption. Genetic studies has revealed genes involved in such metal binding indicating that EPS can be modified for potential enhancement of binding or modification of the types of metals bound. The utility of metal binding to live and dead biomass of Synechocystis has been demonstrated for a range of metals including Cr(VI), Cd(II), Cu(II), Pb(II), Sb, Ni(II), Mn(II), Mn(IV), As(III), As(V), Cs and Hg. The potential of using Synechocystis as a biosorption platform is discussed

New and emerging SXT/R391 integrative conjugative elements as vehicles for stable mobile element transfer and spread of antibiotic resistance in both human and animals.

peer-reviewedThe integrative conjugative elements, ICE s SXT and R391 are the prototypes of a group of gram negative integrative elements known as the SXT/R391 group. R391 was identified in a clinical isolate of Providencia in the late 1960 s in South Africa, while SXT was initially isolated in 1992 in a clinical isolate of Vibrio cholerae O139 and variants have since been isolated in pandemic strains throughout the world. Subsequent sequencing of both elements demonstrated a high degree of structural similarity leading to the group being classified as the SXT/R391 group. The SXT/R391 ICE elements are characterised as integrating into a specific chromosomal site within gram ve hosts, being extremely stable and promiscuous and possessing a number of element hotspots for integration of heterologous DNA including increasingly, antibiotic resistance determinants. This makes such ICE s highly adapted for antibiotic spread. New evidence emerging indicates that SXT/R391-like ICE s are increasingly being identified worldwide particularly in Asia not only from Vibrio species, where they have been found widely in human clinical isolates, but from other gram -ve associated infections of domestic animals and fish. Evidence of more such elements may emerge in the future as a new trapping vector pIceCap has been developed to capture them in a circular form, aiding characterisation. The types of the novel ICE s now emerging, their comparison with prototype elements and the antibiotic resistances associated with them are important given their promiscuous nature and stability. PUBLISHEDPeer reviewe

Analysis and comparative genomics of R997, the first SXT/R391 integrative and conjugative element (ICE) of the Indian Sub-Continent

peer-reviewedThe aim of this study was to analyse R997, the first integrative and conjugative element (ICE) isolated from the Indian Sub-Continent, and to determine its relationship to the SXT/R391 family of ICEs. WGS of Escherichia coli isolate AB1157 (which contains R997) was performed using Illumina sequencing technology. R997 context was assessed by de novo assembly, gene prediction and annotation tools, and compared to other SXT/R391 ICEs. R997 has a size of 85 Kb and harbours 85 ORFs. Within one of the variable regions a HMS-1 β-lactamase resistance gene is located. The Hotspot regions of the element contains restriction digestion systems and insertion sequences. R997 is very closely related to the SXT-like elements from widely dispersed geographic areas. The sequencing of R997 increases the knowledge of the earliest isolated SXT/R391 elements and may provide insight on the emergence of these elements on the Indian sub-continent.PUBLISHEDpeer-reviewe

Ultrasonic intensification as a tool for enhanced microbial biofuel yields

peer-reviewedUltrasonication has recently received attention as a novel bioprocessing tool for process intensification in many areas of downstream processing. Ultrasonic intensification (periodic ultrasonic treatment during the fermentation process) can result in a more effective homogenization of biomass and faster energy and mass transfer to biomass over short time periods which can result in enhanced microbial growth. Ultrasonic intensification can allow the rapid selective extraction of specific biomass components and can enhance product yields which can be of economic benefit. This review focuses on the role of ultrasonication in the extraction and yield enhancement of compounds from various microbial sources, specifically algal and cyanobacterial biomass with a focus on the production of biofuels. The operating principles associated with the process of ultrasonication and the influence of various operating conditions including ultrasonic frequency, power intensity, ultrasonic duration, reactor designs and kinetics applied for ultrasonic intensification are also described

Chapter The Potential of the Photoautotroph Synechocystis for Metal Bioremediation

Pollution & threats to the environmen