Date Published: September 21, 2017
Publisher: Springer Berlin Heidelberg
Author(s): Nirmal Chandra Barman, Fatema Tuj Zohora, Keshob Chandra Das, Md. Golam Mowla, Nilufa Akhter Banu, Md. Salimullah, Abu Hashem.
The study was conducted to select the best promising keratinolytic bacterial strain. A good keratinase positive bacterium isolated from the soil samples of Hazaribagh tannery industrial zone, Dhaka was identified as Arthrobacter genus depending on the conventional techniques and confirmed as Arthrobacter sp. by sequencing 16S rRNA gene. The medium components and culture conditions were optimized to enhance keratinase production through shake flask culture. Keratin and feather powder (10 g/l or 1%) were good substrates for the highest keratinase production along with yeast extract (0.2 g/l or 0.02%) as an organic nitrogen source and potassium nitrate (1 g or 0.1%) as an inorganic nitrogen source. Maximum yield of keratinase was found after 24 h of incubation at 37 °C with an initial pH of 7.0 and inoculums volume 5% under 150 rpm when keratin, yeast extract and potassium nitrate were used as nutrient sources. Keratinase production was more than 5.0-fold increased when all optimized parameters were applied simultaneously. The optimum reaction temperature and pH were determined to be 40 °C and 8.0 respectively for crude keratinase activity. Therefore, Arthrobacter sp. NFH5 might be used for large scale production of keratinase for industrial purposes in less time.
A huge amount of feather and leather wastes are generated every year as a by-product from the poultry and tannery industry due to continuous meat consumption worldwide. Globally over 5 million tons of feathers are produced from poultry-processing plants as a waste product (Poole et al. 2009) every year. Feathers contain a very high content of about 90% keratinous protein, (Onifade et al. 1998; Martinez-Hernandez and Velasco-Santos 2012). These keratins are biologically insoluble, fibrous, recalcitrant and biochemically rigid molecules which are resistant to degradation by most common proteolytic enzymes (McGovern 2000; Riffel et al. 2007; Zaghloal et al. 2011). Native keratin is also highly inert and exhibits usually un-degradable characteristics and lead to persist long term in the environment.
In the present study, bacteria were isolated from collected soil samples and screened for keratinase producing capability on the basis of clear zone formation. The higher clear zone forming isolate on both media was considered as better keratinase producer. The bacterial isolate was gram positive and confirmed as Arthrobacter sp. (NFH5). In most cases, keratin degradation is executed by gram positive bacteria (Gupta and Ramnani 2006). It was also found in previous study that keratinases are produced by coccus Arthrobacter sp. (Pereira et al. 2014). Arthrobacter creatinolyticus KP015744 has been reported as better keratinase producer (Kate and Pethe 2014). Thus Arthrobacter sp. appears to be a potential candidate for keratinase production.