دانلود رایگان مقاله خواص تولید agarase خارج سلولی جدا شده از رسوبات دریایی

abstract

A marine, gram negative, rod shaped bacterium that degrades agar was isolated from the east coast of India and was identified to be Acinetobacter junii PS12B based on 16S rRNA gene sequencing. The effect of different culture conditions, namely pH of the medium, time and temperature of incubation and the agar concentration in the medium, on the agarase production by the strain, was evaluated. The agarase production was significantly (po0.05) affected by the culture conditions. The optimum conditions as determined by response surface methodology were found to be a temperature of 35 °C, pH of 7.0 and time of fermentation of 33 h and agar concentration of 0.5%. Under the optimum conditions, the isolate produced 0.17 units of agarase per ml of the medium. Ammonium nitrate and sodium nitrate were the best nitrogen source in the medium for agarase production by the isolate. Supplementing the agar containing minimal media with simple sugars like glucose and galactose was found to enhance agarase production significantly by two fold. The isolate was also able to degrade carrageenan, which indicates its role in utilization of marine polysaccharides for the production of bioactive oligosaccharides.

4. Discussion

Numerous species of bacterial genera have been reported to be producers of agarase. Most of the reports on agarolytic bacteria are from those isolated from the marine environment (Chi et al., 2012; Fu et al., 2010). Several marine bacteria are known to be agarolytic, examples being Pseudoalteromonas sp. (Jung et al., 2012), Bacillus cereus ASK202 (Kim et al., 1999), Janthinobacterium sp. SY12 (Shi et al., 2008), Micrococcus sp. GNUM-08124 (Choi et al., 2011), Catenovulum sp. X3 (Xie et al., 2013) Agarivorans sp. LQ48 (Long et al., 2010), Bacillus megaterium (Khambhaty et al., 2008). Based on phylogenetic analysis, the strain PS12B found to be Acinetobacter junii. Acinetobacter species are widely distributed in nature and the hospital environment. Tsai et al. (2012) showed that A. junii is a bacterium of low virulence and low mortality rates. However, only certain Acinetobacter species are pathogenic to humans, causing disease mainly in neonates and immunocompromised individuals. The genus Acinetobacter comprises of more than 23 known species and 11 unknown species, which are commonly gram-negative, rod-shaped, non-pigmented, heterotropic, strictly aerobic, polar-flagellated bacteria. There are several species of Acinetobacter from marine environment are known to degrade oil, edible and mineral oils (Tanaka et al., 2010; Luo et al., 2013), and produce enzymes (Fu et al., 2014). Acientobacter junii PS12B isolated in the study was found to be a good candidate for agarase production. Comparing with Acinetobacter sp. reported earlier for agarase isolated from soil environment, the bacterium from the present study could thrive under different conditions as the organism was isolated from marine environment and could degrade marine polysaccharide such as carrageenan. Only one species of Acinetobacter has been reported as agarase producer from the terrestrial environment (Lakshmikanth et al., 2006a). This is the first report on Acinetobacter sp. from marine environment producing agarase enzyme.