Optimization of lipid production in the oleaginous bacterium Rhodococcus erythropolis growing on glycerol as the sole carbon source

The growth of an oleaginous bacteria strain Rhodococcus erythropolis on glycerol was studied. Lipid accumulation was influenced by the glycerol concentration, nitrogen source, nitrogen concentration, pH medium, incubation time and aeration rate. Under the best optimized flask culture medium; 30 g/L glycerol plus 0.75 g/L urea, incubation temperature at 30°C, agitation rate of 150 rpm and 96 h of cultivation time, 3.93 g/L of dry biomass, 1.84 g/L cellular lipid accumulation and 45.8% accumulated lipid of total dry biomass were produced. The scaling up of R. erythropolis in bioreactors yielded the biomass and lipid content of 11.74 g/L and 14.1% of total dry biomass, respectively. The lipid composition of oleaginous microorganisms contained a high proportion of C16 and C18 fatty acids. The extracted lipids were mainly 16.48% C14:1, 16.69% C16:1, 20.16% C16:0, 18.90% C18:1. R. erythropolis could be directed to using raw glycerol obtained from biodiesel by-product as substrate, in order to accumulate lipids for biodiesel production.Key words: Rhodococcus eryhropolis, glycerol, lipid accumulation, biodiesel, fatty acid composition

Examination of the Metallothionein Gene Family in Greater Duckweed <i>Spirodela polyrhiza</i>

Duckweeds are aquatic plants that proliferate rapidly in a wide range of freshwaters, and they are regarded as a potential source of sustainable biomass for various applications and the cost-effective bioremediation of heavy metal pollutants. To understand the cellular and molecular basis that underlies the high metal tolerance and accumulation capacity of duckweeds, we examined the forms and transcript profiles of the metallothionein (MT) gene family in the model duckweed Spirodela polyrhiza, whose genome has been completely sequenced. Four S. polyrhiza MT-like genes were identified and annotated as SpMT2a, SpMT2b, SpMT3, and SpMT4. All except SpMT2b showed high sequence homology including the conserved cysteine residues with the previously described MTs from flowering plants. The S. polyrhiza genome appears to lack the root-specific Type 1 MT. The transcripts of SpMT2a, SpMT2b, and SpMT3 could be detected in the vegetative whole-plant tissues. The transcript abundance of SpMT2a was upregulated several-fold in response to cadmium stress, and the heterologous expression of SpMT2a conferred copper and cadmium tolerance to the metal-sensitive ∆cup1 strain of Saccharomyces cerevisiae. Based on these results, we proposed that SpMT2a may play an important role in the metal detoxification mechanism of duckweed

Removal of lead from battery manufacturing wastewater by egg shell

This research was carried out to investigate the removal of lead from battery manufacturing wastewater by egg shells. The effect of operating parameters i.e., initial pH, contact time, types of egg shell anddose of egg shell were investigated. The characteristics and chemical compositions of egg shells were also investigated and experimental samples were analyzed using AAS, then the data was statistically processedusing least significant difference at a 95% confidence level (p<0.05).The results indicated that the optimum pH for lead removal using 4 types of egg shell was at pH 6, but at this pH final concentration of lead was too low for study of adsorption isotherm. Therefore, unadjustedpH wastewater was used with an initial lead concentration of about 2.365 mg/L, initial pH of 1.35-1.45. Unadjusted pH wastewater decreased the use of expensive chemical reagent for adjusting pH and reducedchemical residues in the environment due to basic properties of egg shell which immediately increased the pH of solution. The optimum dose of egg shell was 1.0 g/100 ml of wastewater with a contact time of 90 minutes. The best adsorbent was natural duck egg shell, which had a significant difference from the othertypes of egg shell. The final concentration of lead was 0.059 mg/L which was lower than the wastewater quality standard. Equilibrium modeling of the adsorption isotherm showed that removal of lead by 4 types of egg shellswere able to be described by the Freundlich model. From this study, precipitation might take part in the adsorption process, especially at the high doses of egg shell which increased the high final pH of solution.Finally, the result of the adsorption isotherm demonstrated that the descending lead removal efficiency was natural duck egg shell, natural hen egg shell, boiled duck egg shell and boiled hen egg shell, respectively