Study On Residential Microbial Communities In Nanjing Based On High-throughput Sequencing And Culturing Methods

Microorganisms are ubiquitous in both natural and manual environments,including the atmosphere,water,soil,and various types of built environments.Microbial communities vary greatly from different environments.Generally,microorganisms originate from a wide range of sources with abundant species,which play important roles in human health,especially in indoor environments.It is reported that people spend about 90%of their life-time in indoor environments,of which,residential environment accounts for 70%.Different types and levels of indoor microbial exposure are closely related to the health of indoor occupants,such as respiratory diseases,acute toxic reactions,allergic diseases such as asthma,etc.With respect to evaluate the health effects and maintain a healthy indoor environment,it is of great significance to study the characteristics of indoor microbial communities and their dynamic evolution.This study investigated the microbial communities in Nanjing,southeast China.Both high-throughput sequencing method and culturing method were employed in this study.Firstly,a longitudinal study was conducted by high-throughput sequencing method in a newly built residence for nine months.Results indicated that the microbial communities originated from indoor air and settled dust varied significantly along different months,but the microbial communities originated from indoor air and settled dust samples in the same month showed high similarity.This suggests that both indoor air and settled dust samples can be used to characterize the indoor microbial community.Then,the cross-sectional study was carried out to investigate microbial communities in indoor and outdoor air from 30 representative residences located in seven administrative districts during summer and winter,respectively.The sequencing results showed that the indoor microbial community was mainly shaped by the outdoor microbial community,and the community structure and composition in the same season but different homes show similarity,however,they in the same home but in different seasons show a huge difference.The bacterial communities were dominated by Proteobacteria phylum,accounting for more than 40%of the total bacterial composition.At the family level,the prevalent bacteria in summer were Sphingomonas（25.3%）,Clostridium（14.8%）and Pseudomonas（7.6%）,while the dominant bacteria in winter were Pseudomonadaceae（57.1%）.The fungal communities were mainly dominated by Ascomycota phylum,accounting for more than 60%of the total fungal composition.At the family level,the dominant fungi in summer were Saccharomycetales＿fam＿incertae＿sedis（8.51%）,Plectosphaerellaceae（4.89%）and Saccharomycetaceae（3.28%）,while the dominant fungi in winter were Pleosporaceae（6.71%）and Herpotrichiellaceae（3.62%）.These results provide informative data at a DNA level to develop the microbial database in China.Similarly,results based on culturing method revealed that indoor microbial concentrations were closely related to outdoor concentrations,and the seasonal dynamics of airborne culturable bacteria and fungi concentrations were much greater than that among different houses or rooms.Specifically,the concentrations of culturable airborne bacteria and fungi were significantly higher in summer than those in winter:854±425 CFU/m³ vs.231±175 CFU/m³ for bacteria and888±776 CFU/m³ vs.620±678 CFU/m³ for fungi,respectively.Most of homes satisfied the Chinese standard for bacteria,i.e.1500 CFU/m³,with about 60%of homes exceed the WHO guideline,i.e.500 CFU/m³.In respect to fungi,nearly 14%-32%of homes exceeded the USA standard,i.e 1000 CFU/m³.The size distribution of indoor culturable airborne bacteria and fungi were single-peak patterned,with the peak concentration usually appeared in the size range of 1.1-2.1μm.It was noted more than 80%of culturable bacteria and fungi appeared in the size range of<4.7μm,which can penetrate into the human lower respiratory tract,especially in summer,accounting for up to 90%.These results provide baseline data to evaluate microbial exposure level and also help engieering control,such as filter selection.Moreover,the effects of environmental factors on the microbial dynamic evolution were explored.Environmental conditions(T,RH,PM_2.5)have important effects on indoor microbial communities and concentrations.Seasonal variations of temperature,humidity and PM_2.5 have important effects on the seasonal dynamics of the indoor microbial community.Besides,the bathroom and kitchen usually have higher microbial concentrations and larger sizes compared to other rooms,which were also associated with higher humidity.More attention should be paid in practice to keep the floor dry and maintain good ventilation in these rooms.These results provide theoretical basis for environment control,especially in terms of humidity.Furthermore,quantitative analysis was carried out to elucidate the relationship between indoor and outdoor concentrations and the size-resolved I/O ratios.Resulted showed that indoor and outdoor microbial concentrations were significantly correlated.The I/O ratios varied insignificantly by seasons,but they differed significantly between bacteria（mostly in I/O>1）and fungi（mostly in I/O<1）,suggesting that indoor sources played a dominant role in bacteria,while outdoor sources in fungi.Specifically,homes with bacteria I/O>1 accounted for 89%and67%in summer and winter,respectively,while homes with fungi I/O<1 in summer and winter accounted for 50%and 73%,respectively.The particle size also made a difference in the I/O ratios.Size-resolved I/O ratios revealed that the smaller the particle size was,the higher the I/O ratio was,suggesting stronger indoor sources.Moreover,the housing characteristics contributed greatly to the I/O ratios,among which,the period of window opening per day,the use of air purifiers and indoor planting played significant roles on the I/O ratio.These results indicate new perspective in size-resolved indoor and outdoor source indentification.