The purple strains of bacteria are an interesting group belonging to the family of Rhodospirillaceae. In this group, we find Rhodopseudomonas (Rp.) palustris, which is known for its ability to produce a clean fuel as H2 [1], a polymer as poly-?-hydroxybutyrate (PHB) [2], a bioactive substance as cis-vaccenic acid (antivirus) [3, 4] and carotenoid type as lycopene [5]. Rhodopseudomonas biomasses are rich in proteins (from 51 to 61 % of dry weight) and they can be used very well as feed stock supplements (Vrati 1984). The underwater tubular photobioreactor (UwTP) is a fully controlled outdoor system for the study of photosynthetic bacteria under anaerobic conditions [2]. We used a 53 L-reactor volume with high performances to investigate on Rhodopseudomonas palustris growth. The growth kinetics of Rhodopseudomonas cells was investigated under a natural light-dark cycle (from sunrise to sunset) and under a forced light-dark cycle (10L/14D). Relationships among solar radiation (SR), biomass output rate (BOR) and growth rate (?) were investigated. After determining the elemental biomass molar composition and its combustion heat, some trends of photosynthetic efficiency (PE) were obtained over daylight. The PE trends always were of oscillatory type, with the exception of that achieved at low biomass concentration. The reason why Rp. cells exhibited this growth behavior was not clear and further studies are in progress. Under a natural light/dark cycle the maximum value of PE was 11.2% at sunset; under a forced light cycle (10L/14D) the highest PE of 8.5% was achieved in the morning. Three initial biomass concentrations were investigated (0.65 g l-1; 1.01 g l-1 and 1.54 g l-1). When the initial biomass concentration was optimal (1.01 g l-1), over the period 11:30 - 13:00, we achieved the highest reactor output rate of 9.91 g (dw) R-1 h-1 and the growth rate reached its maximum value of 0.121 h-1. In the past, the primary goal of photosynthetic microorganism mass-culture systems was to maximize the production of biomass; the second and often equally important goal was to optimize the production of specific biochemicals [6]. Nowadays, optimization of the production of specific biochemicals is surely the most important goal. By scaling up the photobioreactor we can produce biomasses as potential sources of livestock and fish feed. Alternatively, we could produce a specific bioactive substance (cis-vaccenic acid), a thermoplastic polymer (PHB) or a biofuel (H2), which can be more economically successful than biomasses for animal feed.
Investigation on photosynthetic efficiency and growth kinetics of Rhodopseudomonas palustris cultured outdoors, inside an underwater tubular photobioreactor
Carlozzi P;Pushparaj B;Sacchi A;Pinzani E
2006
Abstract
The purple strains of bacteria are an interesting group belonging to the family of Rhodospirillaceae. In this group, we find Rhodopseudomonas (Rp.) palustris, which is known for its ability to produce a clean fuel as H2 [1], a polymer as poly-?-hydroxybutyrate (PHB) [2], a bioactive substance as cis-vaccenic acid (antivirus) [3, 4] and carotenoid type as lycopene [5]. Rhodopseudomonas biomasses are rich in proteins (from 51 to 61 % of dry weight) and they can be used very well as feed stock supplements (Vrati 1984). The underwater tubular photobioreactor (UwTP) is a fully controlled outdoor system for the study of photosynthetic bacteria under anaerobic conditions [2]. We used a 53 L-reactor volume with high performances to investigate on Rhodopseudomonas palustris growth. The growth kinetics of Rhodopseudomonas cells was investigated under a natural light-dark cycle (from sunrise to sunset) and under a forced light-dark cycle (10L/14D). Relationships among solar radiation (SR), biomass output rate (BOR) and growth rate (?) were investigated. After determining the elemental biomass molar composition and its combustion heat, some trends of photosynthetic efficiency (PE) were obtained over daylight. The PE trends always were of oscillatory type, with the exception of that achieved at low biomass concentration. The reason why Rp. cells exhibited this growth behavior was not clear and further studies are in progress. Under a natural light/dark cycle the maximum value of PE was 11.2% at sunset; under a forced light cycle (10L/14D) the highest PE of 8.5% was achieved in the morning. Three initial biomass concentrations were investigated (0.65 g l-1; 1.01 g l-1 and 1.54 g l-1). When the initial biomass concentration was optimal (1.01 g l-1), over the period 11:30 - 13:00, we achieved the highest reactor output rate of 9.91 g (dw) R-1 h-1 and the growth rate reached its maximum value of 0.121 h-1. In the past, the primary goal of photosynthetic microorganism mass-culture systems was to maximize the production of biomass; the second and often equally important goal was to optimize the production of specific biochemicals [6]. Nowadays, optimization of the production of specific biochemicals is surely the most important goal. By scaling up the photobioreactor we can produce biomasses as potential sources of livestock and fish feed. Alternatively, we could produce a specific bioactive substance (cis-vaccenic acid), a thermoplastic polymer (PHB) or a biofuel (H2), which can be more economically successful than biomasses for animal feed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
