He Lei, Yin Kedong, Yuan Xiangcheng
School of Marine Sciences, Sun Yat-sen University, Guangzhou, China.
Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, Guangzhou, China.
Front Microbiol. 2019 Jul 16;10:1593. doi: 10.3389/fmicb.2019.01593. eCollection 2019.
The viruses play an important role in limiting bacterial abundance in oceans and, hence, in regulating bacterial biogeochemical functions. A cruise was conducted in September 2005 along a transect in the deep South China Sea (SCS). The results showed the double maxima in the ratio of viral to bacterial abundance (VBR) in the water column: a deep maximum at 800-1000 m coinciding with the oxygen minimum zone (OMZ) and a subsurface maximum at 50-100 m near the subsurface chlorophyll maximum (SCM) layer. At the deep maximum of VBR, both viral and bacterial abundances were lower than those in the upper layer, but the former was reduced less than the latter. In contrast, at the subsurface maximum of VBR, both viral and bacterial abundances increased to the maximum, with viral abundance increasing more than bacterial abundance. The results suggest that two VBR maxima were formed due to different mechanisms. In the SCM, the VBR maximum is due to an abundant supply of organic matter, which increases bacterial growth, and stimulates viral abundance faster. In contrast, in the OMZ, organic matter is consumed and limits bacterial growth, but viruses are less limited by organic matter and continue to infect bacteria, leading to the maximum VBR. The OMZ in the deep-water column of oceans is over hundreds of years old and receives a constant supply of organic matter from the water above. However, the oxygen level cannot be depleted to anoxia. Bacterial respiration is largely responsible for oxygen consumption in the OMZ; and hence, any process that limits bacterial abundance and respiration contributes to the variation in the OMZ. Viral control of bacterial abundance can be a potential mechanism responsible for slowing down oxygen consumption to anoxia in the OMZ. Our finding provides preliminary evidence that viruses are an important player in controlling bacterial abundance when bacterial growth is limited by organic matter, and thus, regulates the decomposition of organic matter, oxygen consumption and nutrient re-mineralization in deep oceans.
病毒在限制海洋中细菌丰度方面发挥着重要作用，因此，在调节细菌生物地球化学功能方面也发挥着重要作用。2005年9月沿着南海（SCS）深部的一个断面进行了一次航次调查。结果显示，水柱中病毒与细菌丰度之比（VBR）存在双最大值：在800 - 1000米深处出现一个深层最大值，与氧最小值区（OMZ）重合，在50 - 100米处靠近次表层叶绿素最大值（SCM）层出现一个次表层最大值。在VBR的深层最大值处，病毒和细菌的丰度均低于上层，但前者的减少幅度小于后者。相反，在VBR的次表层最大值处，病毒和细菌的丰度均增加到最大值，且病毒丰度的增加幅度大于细菌丰度。结果表明，两个VBR最大值是由不同机制形成的。在SCM中，VBR最大值是由于有机物质的大量供应，这增加了细菌的生长，并更快地刺激了病毒丰度。相反，在OMZ中，有机物质被消耗并限制了细菌的生长，但病毒受有机物质的限制较小，并继续感染细菌，导致VBR达到最大值。海洋深水柱中的OMZ已有数百年历史，并持续从上方水体获得有机物质供应。然而，氧水平不会耗尽至缺氧状态。细菌呼吸在很大程度上导致了OMZ中的氧消耗；因此，任何限制细菌丰度和呼吸的过程都会导致OMZ的变化。病毒对细菌丰度的控制可能是一种潜在机制，有助于减缓OMZ中氧消耗至缺氧状态。我们的发现提供了初步证据，表明当细菌生长受到有机物质限制时，病毒是控制细菌丰度的重要因素，从而调节深海中有机物质的分解、氧消耗和营养物质的再矿化。
