科研之友
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摘要
Soil microorganisms play key roles in ecosystem functioning. Finding tools to accurately measure, quantify and understand this component of soil is crucial to establish relevant indicators of the state of soil. This study proposes an optimized methodology using flow cytometry (FCM) for the quantification of bacteria in soil. This rapid and reproducible methodology was validated in two steps: (a) the recovery of spiked cells from sterilized soil matrix backgrounds and (b) the determination of the total number of bacteria from silty native soils (grassland and crop field). The ratio of counted SYBR Green-stained cells versus expected values amounted to 0.83 on average by FCM, compared to 0.64 by plate counts. We used this FCM method to compare bacterial abundance measured in four types of crop management systems: organic, integrated with (TRC) or without tillage (RTRC) and conventional. The FCM count ranged from 3.91 x 10(8) to 5.69 x 10(8) cells g(-1) soil for crop field and was 6.69 x 10(8) cells g(-1) soil for grassland. Similarly, two other frequently used descriptors of the bacterial community (quantification of the 16S rRNA gene by real-time PCR and total culturable heterotrophic bacteria by plate count analysis) were analyzed for all soils and compared with the FCM data. FCM counts were relevant enough to report significant differences between the four crop management systems. Higher bacterial counts were observed in conventional and integrated RTRC systems in comparison with organic and integrated TRC. The same tendency was observed when considering 16S rRNA gene abundance. As expected, a slight but significant correlation was observed between FCM counts and 16S rRNA gene quantification when considering all soil samples. No difference between crop management systems was noticed if we considered only colony forming unit (CFU) count. A calculated ratio between culturable and total bacterial counts (CFU/FCM) suggests some differences in the culturable proportion according to soil management. In the context of evaluating the state of soil, our FCM method offers a quick and simple assessment of total bacterial abundance in numerous samples. Combined with other biological indicators, FCM contributes to understanding soil bacterial biomass and could represent a useful complement in a larger panel of indicators to evaluate and detect changes in the structure of the soil microbial community.
- 出版日期2015-4
