Seasonal variations of viral- and nanoflagellate-mediated mortality of heterotrophic bacteria in the coastal ecosystem of subtropical Western Pacific

Abstract

Since viral lysis and nanoflagellate grazing differ in their impact on the aquatic food web, it is important to assess the relative importance of both bacterial mortality factors. In this study, an adapted version of the modified dilution method was applied to simultaneously estimate the impact of both viral and nanoflagellate grazing on the mortality of heterotrophic bacteria. A series of experiments was conducted monthly from April to December 2011 and April to October 2012. The growth rates of bacteria we measured ranged from 0.078 h<sup>−1</sup> (April 2011) to 0.42 h<sup>−1</sup> (September 2011), indicating that temperature can be important in controlling the seasonal variations of bacterial growth. Furthermore, it appeared that seasonal changes in nanoflagellate grazing and viral lysis could account for 34% to 68% and 13% to 138% of the daily removal of bacterial production, respectively. We suggest that nanoflagellates grazing might play a key role in controlling bacterial biomass and might exceed the impact of viral lysis during the summer period (July to August), because of the higher abundance of nanoflagellates at that time. Viral lysis, on the other hand, was identified as the main cause of bacterial mortality between September and December. Based on these findings in this study, the seasonal variations in bacterial abundance we observed can be explained by a scenario in which both growth rates and loss rates (grazing + viral lysis) influence the dynamics of the bacteria community

Protozoans bacterivory in a subtropical environment during a dry/cold and a rainy/warm season

“…Similar seasonal patterns with higher protozoans grazing rates during summer periods were also found by other authors in subtropical environments (Tsai et al , 2011, 2012). …”

Interactions among members of the microbial loop in an estuary dominated by microzooplankton grazing

“…In a eutrophic lake, microzooplankton grazing had the greatest impact on bacterial and phytoplankton mortality in summer, while viral lysis was the main control of mortality in winter (Tijdens et al 2008). Microzooplankton grazing and viral lysis removed 33.3 to 66.7% and 13.1 to 137.8%, respectively, of daily bacterial production in the East China Sea (Tsai et al 2012). While grazing on prokaryotes in Mobile Bay removed larger proportions of daily production than measured in the East China Sea (0 to 302%), viral lysis removed variable proportions (0 to 433%) and was detected infrequently.…”

“…Few studies have investigated both microzooplankton grazing and viral lysis in marine systems (Weinbauer & Peduzzi 1995, Evans et al 2003, Kimmance et al 2007, Tijdens et al 2008, Fonda Umani et al 2010, Ortmann et al 2011, Tsai et al 2012, Tsai et al 2013. In these studies, microzooplankton grazing is consistently determined to be the major re moval mechanism of microbial production, while the importance of viral lysis appears to vary across seasons and ecosystems.…”

Bacterial mortality caused by viral lysis in Nha Trang bay, South central Vietnam

“…Trong các thủy vực biển ven bờ, một số nghiên cứu cho thấy, tốc độ phân giải của virus và tốc độ ăn mồi của ĐVNS đến TLCVK tương tự nhau [7,18]. Tuy nhiên, nhiều nghiên cứu khác lại cho thấy, TLCVK chủ yếu do sự phân giải của virus [9,23,24]…”