Cyanobacteria (blue–green algae, BGA) are morphologically diverse group of phototrophic prokaryotes, which occur in almost every habitat on earth and useful to mankind in various ways [3]. They constitute a vast potential resource in varied applications such as food, feed, fuel, fertilizer, medicine, industry and in combating pollution [3]. Until past few decades of research, cyanobacteria were of academic interests and were mostly ignored as nuisance but, now are proved as potential organisms for much biotechnological utilization [4-5,3]. The interest in these organisms as generators of pharmacologically active and industrially important compounds has been stimulated by recent results [6]. A Variety of carotenoids produced by cyanobacteria have important commercial uses. Since carotenoids are non-toxic, they are desirable and used as coloring agents in the food industry [7]. Carotenoids are also well recognized for their antioxidant activity, which is a real asset in the framework of psoriasis; through radical scavenging, carotenoids can reduce the exacerbation of inflammation, thus reducing tissue damage and accelerating repair [8] .Carotenoids are frequently used in dietary additives for poultry and aquaculture farming [9].   

Method of Collection

The soil samples from 5-10 cm deep soil layers were collected using the scalpels. Soil samples were collected in polythene bags of size 6 x 4 inches.

Nutrient Media

The different culture media namely BG-11 [10-12], Allen and Arnon’s medium [13], CFTRI medium [14] and Zarrouk’s medium [15] were used for the rich growth of cyanobacteria. These media were separately used in different sets.

Isolation of cyanobacterial species

The dry soil samples were spread in petri dishes and moistened with sterilized distilled water and cultures were incubated in light. When the visible growth of cyanobacteria begins to appear in the cultures, these cultures were used for the isolation of unialgal cultures of Aphanocapsa biformis.

 Identification of the algal samples 

Morpohometric studies were carried out by using ocular and stage micrometer. The identification of Aphanocapsa biformis was carried out using monograph and keys of Desikachary [1].

Biomass production

For production of biomass, glass bottles (300 mL capacity) were used. The bottles were filled with 100 mL medium and autoclaved. The inoculum was ground in the sterile mortar and pestle in laminar air flow. Then the bottles were inoculated with 5 mL of unialgal suspension of Aphanocapsa biformis and labeled properly. All the cultures were maintained in the culture room at temperature 28±2°C under 8-h light/16-h dark photoperiod with a photosynthetic photon flux density of 40 moles-2S-1provided by cool white fluorescent tube lights .After harvesting, the biomass obtained was subjected to the growth analysis

Estimation of Carotenoids

Carotenoids were estimated by spectrophotometer method according to Gowenlock [2]. Absorbance of carotenoids solution in n- hexane was determined at 440nm and the amount was calculated by comparing with standard. The amount of carotenoids is expressed as % on dry weight basis

Out of the different culture media used, BG-11 medium supported the growth of Aphanocapsa biformis properly as compared to other media used. Allen and Arnon medium also supported growth but after 20 to 25 days, photo bleaching of biomass was observed. Other growth media, such as Fogg’s medium and Zarrouk’s medium supported the growth of Aphanocapsa biformis but the growth rate was very slow.

Yield of biomass is one of the direct measures of quantity of biomass produced per unit area within a specific time. Higher yield indicates higher biomass produced per unit area. Comparison of Aphanocapsa biformisin different media showed that highest biomass per bottle in terms of dry weight was produced in BG-11 medium followed by Allen and Arnon medium.The carotenoids content was more in the Aphanocapsa biformis grown in Fogg’s medium followed by the BG-11 medium. CFTRI medium showed poor response for the carotenoids content (Table 1).

Cyanobacteria are photoautotrophic bacteria and require all the essential major and minor elements. The heterocystous cyanobacteria fix atmospheric nitrogen and they can use atmospheric nitrogen as a source of nitrogen. In bottles, the medium does not come in contact with atmospheric nitrogen and the source needs to be added in the culture medium. If the culture medium is devoid of nitrogen, it results in poor growth of cyanobacteria. Similar results were reported by Olatz [16], medium lacking nitrogen source, results in yellowish green color of the cells which is a characteristic of nitrogen deficiency. In the culture methods like photo- bioreactors, pure nitrogen is continuously bubbled into culture medium, [17-19], so that cultures do not get affected due to nitrogen deficiency. 

Table 1: Influence of Different Media on Growth and Carotenoids in Aphanocapsa Biformis

Values are mean±SE of three independent experiments

The growth of Aphanocapsa biformis was more in BG-11 medium than in other media. For optimum growth of cyanobacteria, appropriate Ka⁺: Na⁺ ratio is required in the cytoplasm. High Na⁺ is required by nitrogen fixing cyanobacteria for conversion of molecular nitrogen into ammonia [20]. BG-11 medium consists moderate concentration of Na⁺ and in Allen and Arnon medium, Zarrouk’s medium and CFTRI medium there is high concentration of Na⁺ while in Fogg’s medium; there is no Na⁺ source. Aphanocapsa biformis is from moist soil habitat, which may not require high concentration of Na⁺ ions in the medium. 

Production of pigments depends on composition of medium and its pH. In Fogg’s medium composition and pH is moderate which resulted in higher accumulation of carotenoides in the biomass of Aphanocapsa biformis.Cifuentes and co-workers [21-22] demonstrated that low nitrogen content results in higher accumulation of carotenoides in Dunaliella sp.This response can be explained by the well-known effect of limitation in this nutrient as an inductive factor of carotenogenesis in Dunaliella [23] .Fogg’s medium does not contain nitrogen source, therefore the higher production of carotenoides may be due to low nitrogen content of the medium.

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