Benjamin Pushparaj

As integrated culture system for outdoor production of microalgae and cyanobacteria

Cultivation of microalgae in closed photobioreactors suffers from high temperatures, whereas in open raceway ponds the optimal temperature is seldom reached. With an integrated device coupling a raceway pond with a suitably sized and positioned closed system (alveolar panel), the heat accumulated in the panel was efficiently transferred to the pond and a near-optimum temperature regimen for Arthrospira platensis was maintained, with no need for any additional cooling device. The productivity obtained in the integrated system was higher than the sum of the productivities (g reactor−1 day−1) of the pond and panel systems operating separately.

Biological constraints in algal biotechnology

In the past decade, considerable progress has been made in developing the appropriate biotechnology for microalgal mass cultivation aimed at establishing a new agro-industry. This review points out the main biological constraints affecting algal biotechnology outdoors and the requirements for making this biotechnology economically viable. One of them is the availability of a wide variety of algal species and improved strains that favorably respond to varying environmental conditions existing outdoors. It is thus just a matter of time and effort before a new methodology like genetic engineering can and will be applied in this field as well. The study of stress physiology and adaptation of microalgae has also an important application in further development of the biotechnology for mass culturing of microalgae. In outdoor cultures, cells are exposed to severe changes in light and temperature much faster than the time scale required for the cells to acclimate. A better understanding of those parameters and the ability to rapidly monitor those conditions will provide the growers with a better knowledge on how to optimize growth and productivity. Induction of accumulation of high value products is associated with stress conditions. Understanding the physiological response may help in providing a better production system for the desired product and, at a later stage, give an insight of the potential for genetic modification of desired strains. The potential use of microalgae as part of a biological system for bioremediation/detoxification and wastewater treatment is also associated with growing the cells under stress conditions. Important developments in monitoring and feedback control of the culture behavior through application of on-line chlorophyll fluorescence technique are in progress. Understanding the process associated with those unique environmental conditions may help in choosing the right culture conditions as well as selecting strains in order to improve the efficiency of the biological process.

Microbial biomass recovery using a synthetic cationic polymer

Abstract A synthetic cationic polymer (Praestol) for biomass recovery by flocculation of Tetraselmis suecica, Spirulina platensis and Rhodopseudomonas palustris was tested both in the laboratory and outdoors. The flocculating efficiency of Praestol increased with the dose used up to 1 mg litre−1 for all microorganisms tested. With this flocculant dose, the percentage of biomass separated was 86% for Rhodopseudomonas and 70% for Tetraselmis and Spirulina. The maximum flocculation efficiency was observed when the flocculant: biomass ratio was 1:1000 (by weight). Moreover, satisfactory flocculation efficiency was maintained when Praestol was used on cultures grown in sea- or brackish-water media. No inhibitory effect on the growth of the cultures was noted when the medium was recycled in the pond after flocculation.

Toxicological analysis of the marine cyanobacterium Nodularia harveyana

Nodularia harveyana, a dinitrogen-fixing cyanobacterial isolate from the Mediteranean Sea, grown in an outdoor photobioreactor, was assayed for its bioactive compounds. The active substance(s) were lypophilic and showed strong allelopathic actvity against other axenic cyanobacteria, antibiotic activity against Gram-positive pathogenic bacteria and antifungal activity against two plant pathogens. The extracts were toxic (LC50 at 30 μL) for grazers such as a rotifer (Brachionus calyciflorus) and a crustacean (Thamnocephalus platyurus).

Production of bio-fuels (hydrogen and lipids) through a photofermentation process.

The purple non-sulfur photosynthetic bacteria Rhodopseudomonas palustris (strain 42OL) was investigated for a co-production of both bio-H(2) and biodiesel (lipids). The investigation was carried out using malic and glutamic acids in a fed-batch cultivation system under continuous irradiances of 36, 56, 75, 151, 320, 500, and 803 W m(-2). Boltzmanns sigmoidal regression model was used to determine growth kinetic parameters during hydrogen photoevolution. The upper limit of volumetric hydrogen photoevolution was 15.5 + or - 0.9 ml l(-1) h(-1). During the entire cultivation period (408 h), the highest average hydrogen production rate (HPR(av)) of 11.1 + or - 3.1 ml l(-1) h(-1) was achieved at an irradiance of 320 W m(-2). Biomasses stored at the end of each experimental set were analyzed in order to determine lipid content, which ranged from a minimum of 22 + or - 1% to a maximum of 39 + or - 2% of biomass dry weight.

Fatty acid composition of Antarctic cyanobacteria

Pushparaj B., Buccioni A., Paperi R., Piccardi R., Ena A., Carlozzi P., and Sili C. 2008. Fatty acid composition of Antarctic cyanobacteria. Phycologia 47: 430–435. DOI: 10.2216/07-90.1 The 31 Antarctic cyanobacterial strains, object of this study, were isolated from south polar lake sediments, soil and lichen associations and belong to the genera of Cyanothece, Chondrocystis, Leptolyngbya, Pseudophormidium, Phormidium, Hormoscilla and Nostoc. They are maintained in the Culture Collection of the Istituto per lo Studio degli Ecosistemi (ISE-CNR, Florence). The fatty acid composition varied among the strains, with relatively high quantities of polyunsaturated fatty acids. Arachidonic acid was found in two strains of Phormidium pseudopristleyi at 24% and 32% of the total fatty acid content. The total lipid content and the C/N ratio varied among strains from 13% to 9% and 3.7 to 11.2, respectively. The diversity of saturated and unsaturated fatty acid composition among the Antarctic strains and their possible application as nutrient supplements are discussed.

Growth physiology of a marine nitrogen-fixing cyanobacterium (Nodularia harveyana) in outdoor culture

The performance ofNodularia harveyana, a N2-fixing cyanobacterium isolated from seawater, has been studied outdoors in two different culture systems: open pond (OP) and tubular photobioreactor (TPR). The productivity in both devices was influenced by areal density. The maximum yield obtained was 12.0 g (d.wt) m−2 day−1 in OP and 14.0 g (d.wt) m−2 day−1 in TPR in August, corresponding to the highest solar radiation received. In a month-long experiment with the cyanobacterium cultivated in TPR at high circulation speed, a net increase in productivity was obtained over that at low circulation speed. The influence of temperature on the productivity of the cultures grown in open ponds and tubular photobioreactors has been investigated. The higher productivity obtained in TPR compared to OP was attributed to its better controlled temperature conditions. In outdoor culture the maximum nitrogenase activity did not coincide with the maximum light intensity, but occurred in early afternoon. The amount of carbohydrate accumulated during the day probably influenced the rate of dark nitrogenase activity and its duration in the night.