Abstract
Virus-like particles (VLPs) are thought to increase the dissolved organic carbon by releasing the contents of the host cell, which, in turn, can affect bacterial growth in natural aquatic environments. Yet, experimental tests have shown that the effect of VLPs on the bacterial growth rate at different depths has seldom been studied. Bacteria–VLP interaction and the effect of VLPs on bacterial growth rate in the sunlit surface (3 m) and dark, deep ocean (130 m) environments were first explored at a test site in the southern East China Sea of the northwest Pacific. Our experimental results indicated that bacterial and virus-like particle (VLP) abundance decreased with depth from 0.8 ± 0.3 × 105 cells mL−1 and 1.8 ± 0.4 × 106 VLPs mL−1 at 3 m to 0.4 ± 0.1 × 105 cells mL−1 and 1.4 ± 0.3 × 106 VLPs mL−1 at 130 m. We found that the abundance of VLPs to Bacteria Ratio (VBR) in the dark deep ocean (VBR = 35.0 ± 5.6) was higher than in the sunlit surface environment (VBR = 22.5 ± 2.1). The most interesting finding is that in the dark, deep ocean region the bacterial growth rate in the presence of VLPs was higher (0.05 h−1) than that in virus-diluted treatments (0.01 h−1). However, there was no significant difference in the bacterial growth rates between the treatments in the sunlit surface ocean region. Deep-sea ecosystems are dark and extreme environments that lack primary photosynthetic production, and our estimates imply that the contribution of recycled carbon by viral lysis is highly significant for bacterial growth in the dark, deep ocean environment. Further work for more study sites is needed to identify the relationship of VLPs and their hosts to enable us to understand the role of VLPs at different depths in the East China Sea.
Highlights
Recent studies concerning large numbers of virus-like particles (VLPs) range from 104 to 108 VLPs mL−1 in both freshwater and marine environments, given that the potential viral lysis may be an important process in altering the carbon flow within the microbial loop [1,2,3]
The correlation of bacterial and VLP abundance suggests that bacterial cells are the principal VLP hosts and support VLP production in aquatic environments [9,10,11]
We hypothesized that the bacterial and VLP abundance, bacterial growth rate, and VLP production would differ between the sunlit surface and the dark, deep ocean layer, due to the physiochemical changes with depth
Summary
Recent studies concerning large numbers of virus-like particles (VLPs) range from 104 to 108 VLPs mL−1 in both freshwater and marine environments, given that the potential viral lysis may be an important process in altering the carbon flow within the microbial loop [1,2,3]. We took preliminary samples from a single site and presented the measurements of bacterial and VLP abundance, bacterial growth rate, and VLP production in the sunlit surface (3 m) and dark, deep ocean environment (130 m) in the southern East China Sea, in October 2020. This is, to our knowledge, the first study examining the role of VLPs from surface to deep waters in the southern East China Sea. We hypothesized that the bacterial and VLP abundance, bacterial growth rate, and VLP production would differ between the sunlit surface and the dark, deep ocean layer, due to the physiochemical changes with depth
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