Aquatic Research

Abstract

Cyanobacteria (blue-green microalgae) is a gram-negative prokaryotic autotroph found in natural waters that plays a pivotal role in biochemical cycles. The present investigation proposed to study the potential of using different concentrations of glucose as the carbon substrate to produce microalgal biomass and biochemical components, such as photosynthetic pigments and total carbohydrates (CH) by Oscillatoria sp. The cyanobacteria were collected, and the isolated colony was found to be Oscillatoria sp., and it was grown in BG-11 medium for mass cultivation. Then, the centrifuged biomass was weighed and used to extract bioactive compounds. Oscillatoria sp. cells were cultured in three different tropic cultures (phototrophic, heterotrophic and mixotrophic) under controlled laboratory conditions with continuous light illumination or unillumination and aeration. Chl–a and total C.H. contents were also evaluated after 120 hrs. The recorded optical density of Oscillatoria was increased from 0.6798 ±0.01 at 660 nm and 0.5847 ±0.01 at 750 nm after 24 hrs to 1.2174±0.002 at 680nm and 1.0243±0.01 at 730nm at the end of 120hrs of the experiment. According to analysis results, the mean amount of Chl-a and Total C.H. of Oscillatoria sp. biomass was determined as 0.5132 µg L-1 and 3.5715 mg mL-1 under the phototrophic culture (absence of glucose), respectively. Under the mixotrophic culture (presence of light), the experimental results showed that the chl-a content was calculated as 0.1770, 0.3380 and 0.7098 µg L-1. In contrast, the total C.H. was calculated as 3.6150, 7.9129 and 11.3191 mg mL-1 in the presence of 2.5, 5 and 10 g L-1 glucose, respectively. Under the heterotrophic culture (absence of light), the results showed that the chl-a content was 0.2366, 0.2456 and 0.2346 µg L-1 while the total C.H. was 4.2969, 8.0990 and 11.5861 mg m L-1 in the presence of 2.5, 5 and 10 g L-1 glucose, respectively. The experimental results showed that the total C.H. content was increased from 3.5715 to 11.58 61 mg mL-1 in the heterotrophic (the absence of light and the presence of 10 g L-1 glucose) BG-11 culture conditions. The chlorophyll-a content was increased from 0.1770 µg L-1 to 0.7098 µg L-1 in the mixotrophic (the presence of glucose and light) BG-11 culture conditions. As a result of the experiment, it was determined that the most suitable culture in terms of total carbohydrate and growth rate was mixotrophic and heterotrophic BG-11 (10 g L-1 glucose) culture condition, and in terms of chl-a was mixotrophic culture (10 g L-1 glucose).