Remediation Effect On The Continuously Cropped Peanut Soil Of Serratia Marcescens RZ-21 And The Optimization Study Of Prodigiosin

Continuous cropping practice is a serious problem in the agriculture industry of our country,and causes a severe decline in peanut yield.Although a number of measures have been taken to improve the situation,there still exit many disadvantages,and they still could not solve this problem.So the first part of our study was to investigate the remediation effect of Serratia marcescens on continuously cropped peanut soil.A pot experiment was conducted under natural conditions to determine peanut agronomic indices,soil microorganism characteristics,soil enzyme activities and antagonism ability to typical pathogens at different growth stages.Four treatments were applied to red soil as follows:an active fermentation liquor of S.marcescens(RZ-21),an equivalent sterilized fermentation liquor(M),an equivalent fermentation medium(P)and distilled water(CK).The result showed that S.marcescens significantly inhibited the two typical plant pathogens Fusarium oxysporum A1 and Ralstonia solanacearum B1 and reduced their populations in rhizosphere soil.The RZ-21 treatment significantly increased peanut yield,vine dry weight,root nodules and taproot length by 62.3,33.0,72.0 and 61.4%respectively,followed by the M treatment.The P treatment also increased root nodules and root length slightly.RZ-21 also enhanced the activities of soil urease,sucrase and hydrogen peroxidase at various stages.In addition,RZ-21 and M treatments increased the average population of soil bacteria and decreased the average population of fungi in the three critical peanut growth stages,except for M in the case of the fungal population at flowering,thus balancing the structure of the soil microorganism community.The results suggest that S.marcescens RZ-21 has the potential to improve the soil environment and agricultural products and thus allow the development of sustainable management practices.In view of the results above and the fuction of S.marcescens reported in other references,we assumed that prodigiosin also functioned in the process of antagonism and soil remediation.However,its production is poor as the secondary metabolite of microorganism.So in the latter two parts,we dedicated in the enhancement of prodigiosin to improve the application value of the bacteria.Firstly,a single factor experiment was conducted to screen the effective elements from different carbon and nitrogen sources,surfactants,fatty acids,metabolites and Metal inorganic salts.Glycerol,FeSO4·7H2O,MgSO4·7H2O,MnSO4·H2O,CaCl2 and NaAc were selected.Then the Plackett-Burman experiment was designed to screen the most three important factors that affects the prodigiosin production.And the three factors,FeSO4·7H2O,glycerol and CaCl2,were found.And then steepest ascent method was designed to confirm the central point of these three factors.At last,the Box-Behnken design experiment was conducted,and the optimal fermentation medium was confirmed.The medium was as follows:sucrose 25 g/L,peptone 25 g/L,glycerol 0.26%,FeSO4·7H2O 0.23mM and CaCl2 16.68mM.In this condition,the prodigiosin was 1450.36 mg/L,and was 5-fold than CK.Secondary,on the base of the optimized medium obtained from the experiment above,we conducted the following experiment in the 5 L fermentation reactor.And the strain biomass,prodigiosin production,sucrose concentration and dissolved oxygen level were investigated under three different agitation conditions(250rpm,300rpm and 350rpm).We found that the agitation speed played a vital role in the strain growth period.According to the result,a two-stage agitation regulation strategy was proposed.That is,the agitation speed was controlled at 300rpm from 0 to 12h,and then was gradually switched to 350rpm after 12h.In this condition,the prodigiosin production was 2167.48 mg/L,and the production rate was 90.31 mg/L/h.The fermentation period was significantly shortened and the prodigiosin production was 7.5-fold more than CK.We compared the expression of four prodigiosin biosynthesis related genes under the optimized condition with CK.We found that the expressions of pig F,pig N and cue R were significantly enhanced,which provides an evidence for the enhancement of prodigiosin production.