Soil bacteria are important drivers of terrestrial ecological processes. As a key regulator of bacterial diversity and activity, autochthonous soil viruses (mostly are bacteriophages) are capable to sense and respond to the changes in environmental factors, and then target and lyse some bacterial populations that involved in regulating biogeochemical cycling. It is considered that about 30% - 50% of bacterial deaths in soil are related to viral regulation.
However, due to the high heterogeneity in soil, the interaction between viruses and bacteria in soil has always been ignored by studies.
Moreover, limited knowledge explains how autochthonous soil viruses respond to nitrogen addition, and how they regulate bacterial composition, thus driving nitrogen cycling.
Paddy land shows lower soil heterogeneity than that in upland, which provides researchers an excellent model for studying the interaction between viruses and bacteria.
To learn the process of soil virus-bacterium interaction induced by irrigation, and application of urea fertilizer, a research team led by Prof. XU Hui from Institute of Applied Ecology, Chinese Academy of Sciences conducted an observational study at a long-term fertilized paddy field (since 1991) at the National Field Observation and Research Station of Shenyang Agro-ecosystems.
The dynamics of viral and bacterial abundances were investigated by epifluorescence microscopy, viral and bacterial communities were observed by randomly amplified polymorphic DNA-PCR combined capillary electrophoresis, and high throughput 16S rDNA amplicon sequencing, respectively, and nitrogen and carbon related gas emissions were measured by gas chromatography.
According to the achievement of this study, soil viruses responded rapidly to the urea addition, and a host-specific viral regulation was triggered, which subsequently modified the soil bacterial composition and functions.
Also, in respond to urea addition, viruses switch to temperate strategies in a short term. This strategy “piggy back the winner”, which reported previously in aquatic ecosystem, was reported firstly in the agricultural ecosystem by this study.
In addition, scientists found that in response to the urea addition, viruses selectively lysed bacterial hosts’ populations with specific functions, such as N cycling groups, thus regulating soil nutrients. Moreover, Methanosarcina, one of the chief CH4 producing archaea, became the biggest beneficiary during this viral top-down regulation.
This study is different than others by bringing targeted experiments to characterize a fertilization effect on soil viral communities, which takes on the tremendous challenge of characterizing viruses in soil. Overall, this work brings in much needed analyses of viruses in soils with some literature context for possible strategies the viruses use to persist.
This study was published online in Viruses entitled "Dynamics of bacterial and viral communities in paddy soil with irrigation and urea application".
Email: yueqian@iae.ac.cn
Publication Name: LI Yuting et al.
