Glycogen, poly(3-hydroxybutyrate) and pigment accumulation in three Synechocystis strains when exposed to a stepwise increasing salt stress.

The cyanobacterial genus Synechocystis is of particular interest to science and industry because of its efficient phototrophic metabolism, its accumulation of the polymer poly(3-hydroxybutyrate) (PHB) and its ability to withstand or adapt to adverse growing conditions. One such condition is the increased salinity that can be caused by recycled or brackish water used in cultivation. While overall reduced growth is expected in response to salt stress, other metabolic responses relevant to the efficiency of phototrophic production of biomass or PHB (or both) have been experimentally observed in three Synechocystis strains at stepwise increasing salt concentrations. In response to recent reports on metabolic strategies to increase stress tolerance of heterotrophic and phototrophic bacteria, we focused particularly on the stress-induced response of Synechocystis strains in terms of PHB, glycogen and photoactive pigment dynamics. Of the three strains studied, the strain Synechocystis cf. salina CCALA192 proved to be the most tolerant to salt stress. In addition, this strain showed the highest PHB accumulation. All the three strains accumulated more PHB with increasing salinity, to the point where their photosystems were strongly inhibited and they could no longer produce enough energy to synthesize more PHB.

Biotechnological conversion of spent coffee grounds into lactic acid.

This work investigates the potential bioconversion of spent coffee grounds (SCG) into lactic acid (LA). SCG were hydrolysed by a combination of dilute acid treatment and subsequent application of cellulase. The SCG hydrolysate contained a considerable amount of reducing sugars (9·02 ± 0·03 g l-1 , glucose; 26·49 ± 0·10 g l-1 galactose and 2·81 ± 0·07 g l-1 arabinose) and it was used as a substrate for culturing several lactic acid bacteria (LAB) and LA-producing Bacillus coagulans. Among the screened micro-organisms, Lactobacillus rhamnosus CCM 1825 was identified as the most promising producer of LA on a SCG hydrolysate. Despite the inhibitory effect exerted by furfural and phenolic compounds in the medium, reasonably high LA concentrations (25·69 ± 1·45 g l-1 ) and yields (98%) were gained. Therefore, it could be demonstrated that SCG is a promising raw material for the production of LA and could serve as a feedstock for the sustainable large-scale production of LA. SIGNIFICANCE AND IMPACT OF THE STUDY: Spent coffee grounds (SCG) represent solid waste generated in millions of tonnes by coffee-processing industries. Their disposal represents a serious environmental problem; however, SCG could be valorized within a biorefinery concept yielding various valuable products. Herein, we suggest that SCG can be used as a complex carbon source for the lactic acid production.

Chicken feather hydrolysate as an inexpensive complex nitrogen source for PHA production by Cupriavidus necator on waste frying oils.

The chicken feather hydrolysate (FH) has been tested as a potential complex nitrogen source for the production of polyhydroxyalkanoates by Cupriavidus necator H16 when waste frying oil was used as a carbon source. The addition of FH into the mineral salt media with decreased inorganic nitrogen source concentration improved the yields of biomass and polyhydrohyalkanoates. The highest yields were achieved when 10 vol.% of FH prepared by microwave-assisted alkaline hydrolysis of 60 g l-1 feather was added. In this case, the poly(3-hydroxybutyrate) (PHB) yields were improved by more than about 50% as compared with control cultivation. A positive impact of FH was also observed for accumulation of copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) when sodium propionate was used as a precursor. The copolymer has superior processing and mechanical properties in comparison with PHB homopolymer. The application of FH eliminated the inhibitory effect of propionate and resulted in altered content of 3-hydroxyvalerate (3HV) in copolymer. Therefore, the hydrolysed feather can serve as an excellent complex source of nitrogen for the polyhydroxyalkanoates (PHA) production. Moreover, by the combination of two inexpensive types of waste, such as waste frying oil and feather hydrolysate, it is possible to produce PHA with substantially improved efficiency and sustainability. SIGNIFICANCE AND IMPACT THE STUDY: Millions of tons of feathers, important waste product of poultry-processing industry, are disposed off annually without any further benefits. Thus, there is an inevitable need for new technologies that enable ecologically and economically sensible processing of this waste. Herein, we report that alkali-hydrolysed feathers can be used as a complex nitrogen source considerably improving polyhydroxyalkanoates production on waste frying oil employing Cupriavidus necator.

Use of controlled exogenous stress for improvement of poly(3-hydroxybutyrate) production in Cupriavidus necator.

The PHB production by Cupriavidus necator H16 depends on the type and concentration of stress factors and on the time of stress application. Hydrogen peroxide and ethanol significantly enhanced PHB accumulation in C. necator cells. Improved yields (10.9 g/L PHB) were observed after exposure of bacterial culture to 0.5 mmol/L H2O2 at the beginning of cultivation and to additional peroxide stress (5 mmol/L H2O2) after 60 h of cultivation (beginning of the stationary phase). Production was then approximately 28 % higher than in control (8.50 g/L PHB). The highest yields (11.2 g/L PHB) were observed when ethanol (0.5 %) was applied at the beginning of stationary phase. An application of exogenous stress could thus be used as a simple strategy for a significant improvement of PHB production in C. necator.