A high Mn(II)-tolerance strain, Bacillus thuringiensis HM7, isolated from manganese ore and its biosorption characteristics

Abstract

Microorganisms play a significant part in detoxifying and immobilizing excessive metals. The present research isolated a strain (HM7) with high Mn(II) tolerance from Mn(II)-contaminated soil samples. The 16S rDNA sequence analysis showed that HM7 had a 99% similarity to Bacillus thuringiensis, which can survive under a high concentration 4,000 mg/L of Mn(II), and the highest removal rate was up to 95.04% at the concentration of 400 mg/L. The highest Mn(II) removal rate was detected at the contact time 72 h, temperature 30 °C, and pH 5.0, while the differences in strain growth and Mn(II) removal rate among different inoculation doses were insignificant. Scanning electron microscopy indicated B. thuringiensis HM7 cells appeared irregular and cracked under Mn(II) stress. Fourier transform infrared exhibited that functional groups like carboxyl, hydroxyl, amino, sulfhydryl groups, and amide bands might take part in the complexation of Mn(II). In addition, HM7 suggested the ability of indoleacetic acid production, siderophore production, and P’ solubilization potential. Therefore, HM7 might have a potential to promote metal absorption by changing the form of heavy metals, and the experiments supported the application of B. thuringiensis HM7 as a biological adsorbent in Mn(II) contaminated environment remediation.

Tolerance and reduction of Cr(VI) by Bacillus amyloliquefaciens, B. thuringiensis and Paenibacillus sp., isolated from Pasto River

“…A similar phenomenon was observed by Huang et al (2020) when evaluating the biosorption capacity of Mn(II) in a concentration range of Mn(II) (0-10000 mg/L) by the B. thuringiensis HM7 strain. The results showed that the growth of HM7 within a concentration range (200 -800 mg/L) was greater than without Mn(II) (Huang, et al, 2020). The effect of Cr(VI) concentrations on the population density of Paenibacillus sp.…”

“…This phenomenon may be due to the bacteria adapting differently to conditions of the environment, depending on the tolerance mechanism that these use (Dhal, et al, 2013;Rath, et al, 2014;Rath, et al, 2019). A similar phenomenon was observed by Huang et al (2020) when evaluating the biosorption capacity of Mn(II) in a concentration range of Mn(II) (0-10000 mg/L) by the B. thuringiensis HM7 strain. The results showed that the growth of HM7 within a concentration range (200 -800 mg/L) was greater than without Mn(II) (Huang, et al, 2020).…”

A High Manganese-Tolerant Pseudomonas sp. Strain Isolated from Metallurgical Waste Heap Can Be a Tool for Enhancing Manganese Removal from Contaminated Soil

“…Other researches observed the low Mn 2+ adsorption rate in an acidic condition (pH < 5), caused by the large amounts of protons like H 3 O + and H + , which increased the difficulty in binding sites of Mn 2+ to cell walls. When pH increased the higher removal rate was reached, which could be connected with more negatively charged cells available, promoting a greater metal uptake [34]. Another reason of this observation is that under acidic conditions, the carboxyl groups responsible for the retention of metals are protonated and restrict entry of metallic ions, whereas at a higher pH, these groups are negatively charged, facilitating the binding of the metals ions [43,44].…”

“…MSB 5 isolated from Sanindipur mines was also viable at even a 1000 mM concentration of MnCl 2 [5]. Meanwhile, Bacillus thuringiensis HM7 isolated from Xiangtan Mn ore in China was able to grow at 31.78 mM [34].…”

Unraveling the Underlying Heavy Metal Detoxification Mechanisms of Bacillus Species

“…The removal and regulation of Mn by microorganisms is mediated by metal-specific regulators that regulate low or sufficient concentrations of Mn inside the cell. This system is well characterized in bacteria, especially Gram-positive bacteria such as Bacillus spp., due to the fact that many studies have reported Mn bioremediation by Bacillus [ 44 , 151 , 152 , 153 ], whereas the Mn homeostasis mechanisms have been studied extensively over the years ( Table 1 ). In B. subtilis, Mn concentration is regulated by MntR, an Mn-specific metallo-regulator related to the DtxR/IdeR family [ 181 ], which serves important roles in the sensing of metals such as iron (Fe) and Mn in several bacterial species [ 189 ].…”