Coprinus comatus endophytic bacteria characteristics and mechanisms for the cadmium resistance

Characteristics and resistant mechanisms of macro-fungus endophytic bacteria to cadmium (Cd) have not been well defined. Strains L1 and L3 with Cd-resistant capacity were isolated from the fruiting body of Coprinus comatus, which were identified as Bacillus sp. Under the stress of Cd, the morphologies of both L1 and L3 changed to reduce the threat of Cd. The results of Fourier Transform Infrared Spectrometry indicated that functional groups such as -OH, -COOH, and -NH₂ participated in the Cd adsorption process. The contents of Cd adsorbed on the cell wall of L1 were 83.46-174.51% higher than that of L3. On the contrary, the contents of Cd accumulated in L1 cytoplasm were 38.77-74.77% lower than that of L3. As the level of Cd increased from 10 to 30 mg/L, the percentages of Cd distributed on the cell walls of L1 and L3 increased by 42.43% and 26.78%, respectively. The results also revealed that the contents of Cd absorbed by the sterilized strains L1 and L3 were 47.67-64.94% and 8.65-78.63% higher than that of living ones, respectively. In addition, the proline production of L1 was 23.75-109.68% higher than that of L3, while the malondialdehyde (MDA) production of L1 was 0.96-15.60% lower than that of L3. Thus, through the comparison of endophytic bacterial physiological responses, the possible characteristics and resistant mechanisms of macro-fungus endophytic bacteria under Cd stress were firstly reported.