Seasonal changes in the concentration and metabolic activity of bacteria and viruses at an Antarctic coastal site

Abstract

Bacteria play a key role in the world's oceans, supporting nutrient remineralisation and mediating carbon transfer. Little is known about annual changes in bacterial concentration, production and metabolism during the extreme seasonal changes in biological productivity in Antarctic waters. We measured rates of bacterial production, concentrations of viruses and bacteria and environmental parameters between February 2004 and January 2005 at an Antarctic coastal site. Concentrations of total bacteria and viruses were obtained using 4', 6-diamidino-2-phenylindole (DAPI) and SYBR Green I (Molecular Probes), respectively. Populations of bacteria in different metabolic states were estimated using vital stains. Concentrations of bacteria with intact or compromised plasma membranes were estimated using BacLight (Molecular Probes) and active cells estimated using 6-carboxyfluorescein diacetate (6CFDA). Our study showed 6CFDA and BacLight gave rapid and ecologically valuable insights into bacterial physiology, production and growth in natural Antarctic communities that were poorly represented by changes in total cell concentrations. Concentrations of total, active and intact bacteria declined rapidly at the end of summer probably owing to viral infection and microheterotrophic grazing. The decline continued over winter, likely owing to substrate limitation, and concentrations only increased after the phytoplankton bloom in spring and summer. Bacterial abundance was positively correlated with particulate organic carbon (POC) and nitrogen (PON), but not dissolved organic carbon (DOC), reflecting the refractory nature of the DOC pool. Only active and intact bacteria were significantly correlated with concentrations of chl a and rates of bacterial production. Furthermore, the obtained rates of [ 3 H]thymidine uptake suggest that bacterial growth rates can be sustained by the populations identified as intact or by active cells alone.

Ocean acidification of a coastal Antarctic marine microbial community reveals a critical threshold for CO<sub>2</sub> tolerance in phytoplankton productivity

“…The low bacterial productivity and abundance of the initial community is characteristic of the post-winter bacterial community in Prydz Bay where growth is limited by organic nutrient availability (Pearce et al, 2007). Whilst an increase in cell abundance was observed at CO 2 levels ≥ 634 µatm (Fig.…”

“…Samples for POM analysis, particulate organic carbon (POC), and particulate organic nitrogen (PON) were collected following the method of Pearce et al (2007). Equipment for sample preparation was soaked in Decon 90 (Decon Laboratories) for > 2 days and thoroughly rinsed in MilliQ water before use.…”

“…Bacterial populations respond to increases in phytoplankton primary productivity by increasing their productivity and abundance, with maximum abundance often occurring after the peak of the phytoplankton bloom (Pearce et al, 2007). High CO 2 levels have been observed to have either no effect on abundance and productivity (Grossart et al, 2006;Allgaier et al, 2008;Paulino et al, 2008;Baragi et al, 2015;Wang et al, 2016) or increase growth rate and production only during the postbloom phase of an experiment (Grossart et al, 2006;Sperling et al, 2013;Westwood et al, 2018).…”

Seasonal to hour variation scales in abundance and production of total and particle-attached bacteria in the open NW Mediterranean Sea (0–1000 m)

“…However, marine microbial observatories generally rely on coastal areas. Indeed, numerous studies have shown that bacterial abundance and activity vary at a seasonal scale G. Mével et al: Short-term variation in bacterial abundance and production in a large number of coastal waters (Shiah and Ducklow, 1994;Pinhassi and Hagström, 2000;Gerdts et al, 2004;Pearce et al, 2007;Sapp et al, 2007), but considerably less information is available in open Ocean (Ducklow and Carlson, 1992). Substrate availability and, to a lesser extent, temperature have been to be the main driving forces of bacterial abundance and production at a seasonal scale (Wikner and Hagström, 1999;Lemée et al, 2002).…”

High single-cell metabolic activity in Antarctic sea ice bacteria

“…Although a lower percentage of cells (~60%) were detected by Junge et al (2004) in sea ice sampled during the Arctic winter, this is likely to reflect seasonal variation in bacterial activity (e.g. Pearce et al 2007), and in general FISH detection rates appear to be significantly higher in sea ice than in other systems.…”