Investigating The Influence Of Stochastic Process On Community Assembly Using Synthetic Microbial Consortia

The mechanism of microbial community assembly have always been the focus of research in the fields of Microbial Ecology and Environmental Microbiology.It is of great significance to the development of microbial resources,to clarify the relationship between microbial communities and their habitats,to reveal the relationship between community structure and function,and to direct the regulation of microbial community functions.A large number of investigations based on high-throughput sequencing(upbottom research)revealed that the driving forces of microbial community assembly can be divided into two aspects: the deterministic factors,including environmental selection pressure,microbial adaption to the environmental and microbial interaction,and the stochastic process,including immigration and emigration of the microorganisms.However,the top-down investigation only shows the relative importance of two aspects in community assembly,and it is difficult to study the influence of only a single factor on community assembly.Recently,researchers start to study the influence of single factors,such as pairwise interactions of microorganisms and different environmental conditions,on the assembly of microbial communities by constructing synthetic microbial communities,that is,bottom-up strategy.However,these studies mainly focus on deterministic factors,while little attention has been paid to random factors.Therefore,we selected 20 bacterial strains isolated from the same soil environment near the Weiming lake of Peking university,and construct a synthetic microbial community.by applying now commonly used diluted-growth cycles,we simulate the succession and assembly of microbial community.We focus on the effect of the stochastic process,that is emigration and immigration,on the community assembly.The main results are as follows:(1)In order to study the impact of different degrees of emigration on community assembly,different degrees of dilution were used to simulate different level of migration.The results showed that the continuous increase of dilution faster the loss of community diversity,mainly due to the bottleneck effect.Shannon index decreased from 2.2 to around 0.5.In addition,with the increase of the dilution degree,the abundance of some strains with fast growth rate but weak competitiveness was significantly increased,that is,the high-level of migration would drive to directional enrichment of these kind of microorgrainms.(2)In order to study the impact of different levels of immigration on community assembly,different levels of immigration were used to simulate different levels of immigration,and low-dilution passages were used to simulate the situation of block the effect of immigration.The result reveled that when the level of immigration was equal to the emigration,the community still maintained high diversity.Shannon index is around 2.2.In contrast,when level of immigration was lower than the emigration,the final diversity of the community was lower.Shannon index is only about 1.3.Therefore,equal-level migration will significantly reduce the loss of community diversity and benefit the maintenance of community diversity.At low levels,community diversity is still lost with passage.Comparing with the situation of low level migration,the community diversity is still higher than,which indicates that the community diversity can be maintained.(3)In order to further study the impact of immigration and emigration on the community assembly at the same time,the passage was carried out through high dilution,and strains of different densities were migrated at the same time.As a result,it was found that at high levels of immigration,the community still maintains a high diversity.Shannon index ranges from 1.5 to 2.5.When equal levels or low levels of immigration,the final diversity of the community is low.Shannon index is only about 0.5.Further comparing the immigration experiment with the emigration experiment,it was found that there is a significant difference between the two when immigration at the same level.In the immigration experiment,equal level migration can slow down the loss of community diversity.In the immigration and emigration experiments,equal level immigration cannot slow the loss of community diversity.It can be concluded from this that in the presence of emigration factors,high level immigration can significantly reduce the diversity of the community,but when equal level or low level of immigration,the diversity of the community is still lost quickly.The impact of immigration on community assembly is less than the impact of emigration.By means of the synthetic microbial system,we controlled other factors,and systemically investigate the influence of emigration and immigration on the succession and assembly of microbial community.The conclusion draw here will help to further understand the mechanism of microbial community assembly and the formation of biodiversity,and also provide important clue to the application of synthetic microbial consortium on the production of valuable products.It has certain guiding significance for environmental protection.