Isolation and screening of heavy metal resistant ammonia oxidizing bacteria from soil and waste dump: a potential candidates for bioremediation of heavy metals

Abstract

12The study was undertaken to examine the response of ammonia oxidizing bacteria to 13 different heavy metal salt in an elevated concentration. Surface soil samples at depth of 0-15 14 cm were collected at random from Akwa Ibom State University in Akwa Ibom State, soil 15 sample from University of Nigeria, Nsukka and from solid waste disposal site in Uyo, Akwa 16 Ibom State. The response of heavy metal salt on Ammonia Oxidizing bacteria(AOB) isolated 17 from soil samples were investigated by supplementing different heavy metal salts namely, 18 copper(Cu),nickel (Ni), lead (Pb) and cadmium (Cd) at four loading rates(100,200,500,1000 19 µg/ml) in mineral salt broth with Ammonia Oxidizing Bacteria (AOB) isolate. The cultures 20were incubated for 7 days. Growth of AOB was measured by withdrawing samples from the 21 medium every 24 hours and absorbance of the turbidity measured at 600 nanometre using 22 spectrophotometer. All bacteria showed high tendency to decrease optical density while 23 increasing metal concentration in the medium. Tolerance for the metal ions was dependent on 24 concentration, time and the isolate tested. All the Ammonia oxidizing bacterial (AOB) showed 25 a high level of tolerance for the metals tested, and exhibited good growth at all metal salt 26 concentrations tested. These make the nitrifying bacteria attractive potential candidates for 27 further investigations regarding their ability to remove metals from contaminated soil. 28 IMPORTANCE:The aim of this study is tolerance of ammonia oxidizing bacteria 29 growth to heavy metal. Nitrifying bacteria remain a good option for bioremediation of soil 30 and waste dump, since it is regarded as eco-friendly and efficient in biosorption of heavy 31 metal. The study is significant to the field of environmental microbiology by adding to 32 knowledge in bioremediation. Hadia and Ahmed, 2018). Amongst the pollutants that are of environmental and public health 37 concerns due to their toxicities are: heavy metals, nuclear wastes, pesticides, greenhouse gases, 38 and hydrocarbons. These toxic pollutants are discharged from specific locations worldwide and 39 thus pollute specific regions. These pollutants have different toxicity and chemical behaviour 40 (Nibourg et al., 2013). Environmental contamination caused by heavy metals (HM) has received 41 increased attention worldwide (Gupta et al., 2016;Sharma, 2016; Ayangbenro and Babalola, 42 2017; Liu et al., 2018). Heavy metal (HM) is any metallic element that has a relatively high 43 density and is toxic or poisonous at low concentrations. Heavy metals are elements with atomic 44 number higher than 20, an atomic mass greater than 40 g and a specific weight of more than 5 45 g/cm 3 (Canli et al., 2003; Hamsa et al., 2017). These elements often find their way into soil 46 through environmental contaminants including the atmospheric pollutants in industrial regions 47 (emissions from the rapidly expanding industrial areas), unlimited use of agricultural fertilizers, 48 mine tailings, disposal of high...