Subhasree Ray

Bioconversion of crude glycerol to polyhydroxyalkanoate by Bacillus thuringiensis under non-limiting nitrogen conditions

Glycerol has emerged as a cheap waste material due to blooming biodiesel manufacturing units worldwide. The need is to exploit the crude glycerol (CG) to produce useful products such as polyhydroxyalkanoate (PHA). Bacillus thuringiensis EGU45 was found to produce 1.5-3.5 gP HA L(-1) from feed containing 1-10% CG (vv(-1)) and nutrient broth (NB, 125 mL) without any acclimatization. B. thuringiensis EGU45 could produce PHA at the rate of 1.54-1.83 g L(-1), from 1% CG (vv(-1)) on media having high nitrogen contents: (i) NB, (ii) NB+0.5% NH4Cl (wv(-1)), and (iii) peptone+yeast extract+0.5% NH4Cl (wv(-1)). B. thuringiensis EGU45 was able to produce co-polymer of P(3HB-co-3HV) with 13.4% 3HV content on high N containing feed supplemented with propionic acid. This is the first report demonstrating the abilities of B. thuringiensis to convert CG into PHA co-polymer under non-limiting N conditions.

Production of co-polymers of polyhydroxyalkanoates by regulating the hydrolysis of biowastes

Production of polyhydroxyalkanoate (PHA) co-polymers by Bacillus spp. was studied by feeding defined volatile fatty acids (VFAs) obtained through controlled hydrolysis of various wastes. Eleven mixed hydrolytic cultures (MHCs) each containing 6 strains could generate VFA from slurries of (2% total solids): pea-shells (PS), potato peels (PP), apple pomace (AP) and onion peels (OP). PS hydrolysates (obtained with MHC2 and MHC5) inoculated with Bacillus cereus EGU43 and Bacillus thuringiensis EGU45 produced co-polymers of PHA at the rate of 15-60mg/L with a 3HV content of 1%w/w. An enhancement in PHA yield of 3.66-fold, i.e. 205-550mg/L with 3HV content up to 7.5%(w/w) was observed upon addition of OP hydrolysate and 1% glucose (w/v) to PS hydrolysates. This is the first demonstration, where PHA co-polymer composition, under non-axenic conditions, could be controlled by customizing VFA profile of the hydrolysate by the addition of different biowastes.

Dark fermentative bioconversion of glycerol to hydrogen by Bacillus thuringiensis

Biodiesel manufacturing units discharge effluents rich in glycerol. The need is to convert crude glycerol (CG) into useful products such as hydrogen (H2). Under batch culture, Bacillusthuringiensis EGU45 adapted on pure glycerol (PG, 2% v/v) resulted in an H2 yield of 0.646 mol/mol glycerol consumed on minimal media (250 mL) supplemented with 1% ammonium nitrate at 37°C over 4 days. Here, H2 constituted 67% of the total biogas. Under continuous culture, at 2 days of hydraulic retention time, B. thuringiensis immobilized on ligno-cellulosic materials (banana leaves - BL, 10% v/v) resulted in a H2 yield of 0.386 mol/mol PG consumed. On CG, the maximal H2 yield of 0.393 mol/mol feed consumed was recorded. In brief, B. thuringiensis could transform CG, on limited resources - minimal medium with sodium nitrate, by immobilizing them on cheap and easily available biowaste, which makes it a suitable candidate for H2 production on a large scale.

Challenges and Opportunities for Customizing Polyhydroxyalkanoates.

Abstract Polyhydroxyalkanoates (PHAs) as an alternative to synthetic plastics have been gaining increasing attention. Being natural in their origin, PHAs are completely biodegradable and eco-friendly. However, consistent efforts to exploit this biopolymer over the last few decades have not been able to pull PHAs out of their nascent stage, inspite of being the favorite of the commercial world. The major limitations are: (1) the high production cost, which is due to the high cost of the feed and (2) poor thermal and mechanical properties of polyhydroxybutyrate (PHB), the most commonly produced PHAs. PHAs have the physicochemical properties which are quite comparable to petroleum based plastics, but PHB being homopolymers are quite brittle, less elastic and have thermal properties which are not suitable for processing them into sturdy products. These properties, including melting point (Tm), glass transition temperature (Tg), elastic modulus, tensile strength, elongation etc. can be improved by varying the monomeric composition and molecular weight. These enhanced characteristics can be achieved by modifications in the types of substrates, feeding strategies, culture conditions and/or genetic manipulations.

Co-metabolism of substrates by Bacillus thuringiensis regulates polyhydroxyalkanoate co-polymer composition

Polyhydroxyalkanoate (PHA) production by Bacillus thuringiensis EGU45 was studied by co-metabolism of crude glycerol (CG) (1%, v/v), glucose (0.05-0.5%, w/v) and propionic acid (0.05-0.5%, v/v) under batch (shake flask) culture conditions. Glycerol+PA combination resulted in 15-100mg/L PHA co-polymers with a HV content of 33-81mol%. The addition of NH4Cl (0.5%, w/v) to CG+PA enhanced PHA production by 1.55-fold, with a HV content of 58-70mol%. The time period of incubation of PA to the feed: CG+glucose was optimized to be 3h after initiation of fermentation. The PHA contents were found to be stable at 1900-2050mg/L up scaling from 0.4 to 2.0L feed material. Biochemical characterization through GC-MS of PHA co-polymer revealed the presence of 3-hydroxydecanoate (3-HDD), 3-hydroxyoctadecanoate (3HOD), 3-hydroxyhexadecanoate (3HHD).

Biotechnology in Aid of Biodiesel Industry Effluent (Glycerol): Biofuels and Bioplastics

Crude glycerol produced by the biodiesel industries as a waste has gathered significant attention as a cheap carbon source. It was recently realized that this forthcoming problem of waste glycerol may be circumvented through biological routes. The role of glycerol to serve as start material for a plethora of chemicals has been well recognized. The lead of science in the field of biotechnology has broadened the application range of glycerol using microorganisms. Here, we are dealing with the potential of the glycerol for the production of third-generation fuels and polymers. The reduced nature of the glycerol molecule makes it a suitable substrate for these biological processes. It would be worth observing that the rapidly thriving biodiesel industry will certainly assist in offering a low-cost glycerol feed for producing other valuable bioproducts. An integrative approach to merge all these procedures could possibly assist in growing and managing a sustainable energy production.

Biological Significance of Degradation of Polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are biodegradable polymers produced by microbes under nutrient-deprived conditions. These polymers act as food reserves of the organism to survive under adverse environmental conditions. These molecules show high similarity with petroleum-based plastics. Hence, these are promoted as biodegradative alternatives to plastics. PHAs are degraded by the depolymerase enzyme primarily to generate energy for microbial growth. Extracellular degradation occurs on the PHA released from the lysed cell. Various factors are known to influence the degradative process such as humidity, temperature, monomeric composition, etc. The PHA degradation accompanies a decline in the polymer molecular weight and an increase in its crystallinity. Microbes involved in the PHA degradation contribute toward maintenance of ecosystem through the carbon cycle. The by-products of PHA degradation process can be subjected to different biological applications, especially in the energy and medical fields.

Wastewater: A Potential Bioenergy Resource

Wastewaters are a rich source of nutrients for microorganisms. However, if left unattended the biodegradation may lead to severe environmental hazards. The wastewaters can thus be utilized for the production of various value added products including bioenergy (H2 and CH4). A number of studies have reported utilization of various wastewaters for energy production. Depending on the nature of the wastewater, different reactor configurations, wastewater and inoculum pretreatments, co-substrate utilizations along with other process parameters have been studied for efficient product formation. Only a few studies have reported sequential utilization of wastewaters for H2 and CH4 production despite its huge potential for complete waste degradation.

Targeting Quorum Sensing Mediated Staphylococcus aureus Biofilms: A Proteolytic Approach

Staphylococcus aureus infects human through biofilm formed by the process of quorum sensing. Biofilm confers this human pathogen with high resistance to antibiotics. The inhibition of biofilm forming process or dispersal of already formed biofilm can be the potential targets for treating the diseases. Since, the biofilm is made up of exopolysaccharides, proteins and lipids, the action of proteases can hydrolyse the protein component and disrupt the biofilm matrix. Consequently the bacterium so exposed can be eliminated by low doses of antibacterials.

Quorum Sensing and Its Inhibition: Biotechnological Applications

Microorganisms have long been used in various areas of biotechnology. In the recent times what has gained fascination is the communication among microbes, known as Quorum sensing (QS). Fascinating information has been generated on understanding the significance of QS, and its inhibition (QSI), especially in plant, animal and human pathogenesis. Focus has now shifted on exploiting QS and QSIs for biotechnological applications in designing: (i) genetic circuits for producing novel products, (ii) biosensors, (iii) molecules for cancer therapy, etc. Here, we cover a few applications in Health, Agriculture, Aquaculture, Energy and Bioremediation sectors.