Study On The Effect Of Arsenite-oxidizing Bacterium YYS001 On The Accelerated Oxidization Of Arsenite In Paddy Soil

Highly toxic arsenite[As(Ⅲ)]is the main arsenic(As)species in soil solution,also one of the important sources for As(Ⅲ)pollutant in rice grain.The accelerated oxidization of As(Ⅲ)pollutant into As(Ⅴ)by microbe in soil is a convenient method to decrease As(Ⅲ)pollution in rice grain because As(Ⅴ)is more easily removed through soil absorption than As(Ⅲ).In this study,a highly arsenite-oxidizing bacterium,named as YYS001,was isolated from the soil of Zijinshan mining area in Longyan,Fujian province of China.At first,a two-week’s greenhouse culture experiment was used to investigate the effect of YYS001 inoculation concentration,organic carbon and nitrogen types and their concentration,stirring way and inoculation period on the accelerated oxidization of As(Ⅲ)by YYS001 and its colonization in soil so as to obtain the optimal culture parameters.Then,under the optimal culture parameters,indica cultivar Lu You Ming Zhan(LYMZ)was chosen as the experimental materials,a potting culture was used to investigate how the accelerated oxidization of As(Ⅲ)by YYS001 was affected through the determination of As species in soil solution with or without LYMZ,collected at 10 cm down soil surface on different growth stages of LUMZ such as tillering stage,booting stage,pustulation period and mature period,on the other hand,the quantities of YYS001 was further determined by Real-time Quantitative PCR Detecting System(qPCR)to investigate the correlation of YYS001 colonization in soil to its accelerated oxidization for As(Ⅲ).Indexes for morphology and yield and the concentration of different As species in rice grain at mature period of LYMZ were determined to investigate the possibility of controlling the species transformation of As in paddy soil by using arsenite-oxidizing bacterium YYS001 in order to finally control the As toxicity,the intake and accumulation of As in the rice grain.The results of this study will provide a theoretical basis and technical support for controlling the intake of As into the rice plant,which growing in As pollution area.The main conclusions are as follows:1.YYS001 inoculation concentration,organic carbon and nitrogen types and their concentration were the key factors to affect the accelerated oxidization of As(Ⅲ)by YYS001 and its colonization in soil,while stirring way and inoculation period showed no significant effect on the accelerated oxidization of As(Ⅲ)by YYS001 and its colonization in soil.The optimal culture parameters were as followers:the inoculation concentration of isolated YYS001 suspension liquid(2.9×109 cfu/mL)was 10.0 μL/g soil,the added concentration for soybean meal was 3 mg/g soil,no stirring was operated and the inoculation period was 14 days.Under the optimal culture parameters,YYS001 showed the highest accelerated oxidization for As(Ⅲ),9.8 times higher than that without soybean meal added,moreover,the quantities of YYS001 was 10.7 times higher than that without soybean meal added,which meant that YYS001 could colonize well in As-containing soil and accelerate the oxidization of As(Ⅲ).2.Whether LYMZ was planted or not,on the earlier stage of YYS001 inoculation into soil,YYS001 significantly(p<0.01)decreased the concentration of As(Ⅲ)and As(V)in As(Ⅲ)-containing or As(V)-containing soil solution,soybean meal significantly(p<0.01)facilitate the growth of YYS001 and accelerated the oxidization of As(Ⅲ).After YYS001 was inoculated into soil till 27,51,78,96 days,namely the tillering stage,booting stage,pustulation period and mature period of LUMZ,the quantities of YYS001(105～106 cells/g soil)in different treatments with LYMZ were much higher than that(103～104 cells/g soil)in different treatments without LYMZ,while the concentration of As(Ⅲ)and As(V)in different treatments with LYMZ were all significantly(p<0.01)lower than that in different treatments without LYMZ,which showed that continuous radial oxygen loss from LYMZ facilitate the accelerated the oxidization of As(Ⅲ)by YYS001.3.When no rice was planted in As(Ⅲ)-containing soil,soybean meal had no significant effect on YYS001 colonization in soil till 78 days,but significantly(p<0.01)facilitated YYS001 colonization when the As(Ⅲ)-containing soil was regulated by YYS001 till 96 days.While soybean meal significantly(p<0.01)facilitated YYS001 colonization within the total 96 days regulated by YYS001 inoculation when no rice was planted in As(V)-containing soil.When cultivar LYMZ was planted in As(Ⅲ)-containing soil and regulated by YYS001 for 27 days,soybean meal significantly(p<0.01)facilitated YYS001 colonization because of the lower radial oxygen loss from LYMZ,but had no significant effect on YYS001 colonization after regulated by YYS001 more than 27 days because of the higher radial oxygen loss from LYMZ.Therefore,the radial oxygen loss from LYMZ was the predominant factor to facilitate YYS001 colonization within the whole process of rice-planting and soybean meal was the subdominant factor.Whether LYMZ was planted or not in As(Ⅲ)-containing or As(Ⅴ)-containing soil,soybean meal increased the concentration of As(Ⅲ)in soil solution after the As(Ⅲ)-containing or As(Ⅴ)-containing soil was regulated by YYS001 more than 51 days,facilitated the reduction of As(Ⅴ)into As(Ⅲ),and finally weakened the accelerated the oxidization of As(Ⅲ)by YYS001.4.Compared with the treatments(AT3 or AT5)with As(Ⅲ)-containing or As(Ⅴ)containing soil,YYS001 significantly(p<0.01)increased the physiological indexes of LYMZ such as the dry weight of its roots,stems,shoots and leaves,and its grain yield except the shoots from the treatment ATG5,while soybean meal impaired the remediation effect of YYS001 for the above physiological indexes of LYMZ.5.YYS001 significantly(p<0.01)decreased As(Ⅲ)concentration in rice grain of LYMZ from the control treatment without As(Ⅲ)or As(Ⅴ)added into the soil and the treatment with As(Ⅲ)added into the soil,and had on significant effect on As(Ⅲ)concentration in rice grain of LYMZ from the treatment with As(Ⅴ)added into the soil.Soybean meal increased Dimethyl arsenic acid[DMA(Ⅴ)]concentration in rice grain of LYMZ,but significantly(p<0.01)decreased As(Ⅲ)and As(Ⅴ)concentration in rice grain of LYMZ from the treatment with As(Ⅲ)or As(Ⅴ)added into the soil,and showed the highest suppression for inorganic As transportation from soil to rice grain(the treatments ATGN3 and ATGN5).In conclusion,YYS001 could significantly(p<0.01)accelerate the oxidization of As(Ⅲ)in As(Ⅲ)-containing or As(Ⅴ)-containing soil,alleviate the toxicity of As(Ⅲ)and As(Ⅴ)for rice growth,and decrease As(Ⅲ)concentration in rice grain of LYMZ.Soybean meal facilitated YYS001 colonization in soil,decreased As(Ⅲ)and As(Ⅴ)concentration in rice grain of LYMZ,but impaired the remediation effect of YYS001 for the physiological indexes of LYMZ.