Elementary Screening Of Copper-resistant Bacteria And Its Effects On Elsholtzia Splendens Growth And Copper Absortion

Along with the impact of human activities on the environment,copper contamination of soils is becoming more serious.Copper pollution not only inhibits plant growth,but also causes great harm to human health through the food chain.Currently,there are two methods to solve the problem of soil pollution and transfer through the food chain:on the one hand,by reducing the plants’ absorption of heavy metals,thereby reducing the transfer to the food chain;on the other hand,by increasing the concentration of heavy metals in certain plants to remove the heavy metals contamination of soils.The use of methods of plant and microbial bioremediation of heavy metal contaminated soils has drawn attention due to the low-cost,permanent repair efficacy and lack of secondary pollution of these methods.This study attempts to find high copper resistant bacteria,which can be combined with plants,by inoculating the plants in order to understand its effect on plant growth and on the absorption of copper.China’s copper hyperaccumulator plant Elsholtzia splendens is inoculated to study the effects of the screened strains on the plant.Siberia Cocklebur,Creeping Day flower,Elsholtzia splendens and Cockeye weed collected from Daye district(copper mine zone)and Hubei University(non-copper mine zone)were the object of study.Endophytes and rhizosphere soil bacteria were screened and isolated from those plants,and the resistance levels of microorganisms to copper were compared in both zones.Through comparative analysis,it was found that for the same part of the plant,the microorganisms isolated from the plants grown in the copper mine zone have a significantly higher resistance level to copper than the plants from the non-copper mine zone.The resistance level to copper of the rhizosphere bacteria and the root endophytes is higher than the stem endophytes,which in turn is higher than the leaf endophytes.Plant tissue resistance to copper from the underground part to the aboveground part is more and more weak.Experiments isolated a high level of anti-copper strain from the rhizosphere soil of the Cocklebur plant grown in the copper mine zone.This strain is marked as CET.The CET tolerance to Cu2+ can reach up to 9 mmol/L.The CET strain underwent morphological,physiological and biochemical tests as well as the 16SrDNA sequence analysis.The strain was identified as Klebsiella,and the similarity to Klebsiella quasipneumoniae subsp.Similipneumoniae reached up to 98.95%.The CET strain’s growth curve under the Cu2+ stress was experimentally studied.The results showed that low concentrations of Cu2+(1.5mmol/L)promoted the strain’s biomass.On the contrary,high concentrations of Cu2+(6mmol/L)inhibited the strain’s biomass.Intermediate concentrations of Cu2+(3mmol/L)didn’t affect significantly the strains’ biomass but delayed the time entrance in the logarithmic phase.Elsholtzia splendens seed germination and plant growth experiments showed that:at different concentrations of copper stress,CET delayed Elsholtzia splendens seed germination time,but improved the overall germination rate of seeds.Within seven days,the average germination rate increased 2%to 6%.Under copper stress,inoculation treatment promoted the seed root and stem growth,which made the root increase from 14%to 57%and stem increase from 11%to 87.5%.Pot experiment results show that under copper stress,compared with non-inoculated group,the inoculation treatment promoted the growth of Elsholtzia splendens,the average height increased from 28.2cm to 33cm,an increase of 14.5%.The effect of CET strains on the Elsholtzia splendens physiological experiments showed that:under copper stress,CET strains significantly increased the Elsholtzia leaf’s superoxide dismutase(SOD)activity,reducing plant proline content and MDA,ultimately reducing the copper ions peroxidation damage to plants;CET strains improved chlorophyll content and promoted the photosynthesis under stress conditions,thus increasing the height,aboveground and underground plant biomass maintaining plant normal growth.It was also determined the copper content of both the aboveground and underground parts of the plants.The results showed that the copper content of the roots of the plants from the inoculated group was 1.5 times less than from the bacteria group;aboveground copper content is lower than that in the inoculation groups.The results showed that soil inoculation significantly reduced strain CET soil copper ions effectiveness,reduced copper ion transfer rate,thereby reducing the toxicity of copper plant damage.In short,under copper stress inoculation,CET bacteria can significantly promote the growth of Elsholtzia splendens and increase its biomass,reduce the absorption of copper and reduce the damage caused by copper toxicity.