Seasonal variability and regulation of bacterial production in a shallow eutrophic lake

Abstract

The seasonal variation of bacterial production (BP) in a shallow, eutrophic Lake Kasumigaura was clarified from 2012 to 2016. During the studied period, BP fluctuated from 1.9 to 138 μg C L−1 d−1. There were no significant correlations between BP and bacterial abundance in any season, suggesting a strong top‐down regulation on BP throughout the year. On the other hand, BP was also related to bottom‐up regulation factors such as water temperature, phosphorus, and primary production (PP) annually. During winter, BP was positively correlated with chlorophyll a concentration, suggesting that autochthonous substrates were relatively important for BP. Moreover, BP was positively correlated with heterotrophic nanoflagellates, ciliates, and copepods, suggesting higher availability of substrates for BP. In summer, although there was no significant correlation between BP and PP, rainfall amount showed significant negative correlations with both BP and PP, suggesting depressed PP from relatively lower solar irradiance coupled with unfavorable weather conditions that decreased the substrate supply for bacteria. These results suggest that temporal variation of BP was regulated not by allochthonous, but by autochthonous substrates during both the highest (summer) and lowest (winter) productive seasons, even in a shallow, eutrophic lake. PP in autumn was approximately half that of spring due to lower solar irradiance, although water temperatures during both seasons were similar and nutrient concentrations during autumn were higher. On the other hand, BP in autumn was comparable with that in spring, and the bacterial carbon demand (= BP + bacterial respiration; 1.12 ± 0.79 g C m−2 d−1) was comparable to PP (1.16 ± 0.53 g C m−2 d−1), suggesting the relative importance of higher allochthonous substrates relative to other seasons.

Horizontal variability and regulation of bacterial production in Lake Biwa, Japan

“…3). A similar larger BP variation was observed in another lake (Lake Kasumigaura, the second largest lake in Japan) at higher water temperatures; the variations of BP in Lake Kasumigaura were attributed to autochthonous substrate supply of DOC from primary production (Tsuchiya et al 2019). In the present study, BP was positively correlated to TN, phosphorus (TP, PP, DTP, and DOP), DOC, chl a, and turbidity (Fig.…”

“…For measurements of bacterial production (BP), 40 mL of collected lake water was poured into 50-mL centrifuge tubes and incubated with 50 nM of [ 15 N 5 ]-2ʹ-deoxyadenosine ( 15 N-dA, NLM-3895-PK, Cambridge Isotope Laboratories, Inc., Tewksbury, MA, USA) in the dark at in situ temperature for 3-8 h depending on water temperature, according to a previous study (Tsuchiya et al 2019). The incubation was started on board immediately after the sampling.…”

“…Bacterial cells were broken by glass beads in a Fast Prep FP120 Cell Disrupter (speed, 6.0; time, 40 s; MP Biomedicals, Santa Ana, CA, USA), and the released DNA was purified by using magnetic beads, according to the manufacturer's protocols. The DNA recovery efficiency was considered to be 100% (Tsuchiya et al 2019). After the DNA extraction, the samples were processed according to Tsuchiya et al (2015), Tsuchiya et al (2020a)) for quantifying the 15 N-dA incorporation rates.…”

Detection of potentially pathogenic Arcobacter spp. in Bangkok canals and the Chao Phraya River

“…Cells on filters were disrupted using a homogenizer (FastPrep; MP Biomedicals, LLC, Santa Ana, CA, USA) at 6.0 m s À1 for 40 s, after which DNA was purified by using magnetic beads to produce 100 μl of DNA extract. This procedure has been shown to extract DNA with almost 100% recovery rate and with suitable quality for quantitative PCR (qPCRs) (Tsuchiya et al 2019).…”

Incorporation characteristics of exogenous 15N-labeled thymidine, deoxyadenosine, deoxyguanosine and deoxycytidine into bacterial DNA

“…Extractions were performed in accordance with the manufacturer's protocols. The DNA extraction efficiency was considered as 100% [14]. After the DNA extraction, the DNA sample was enzymatically hydrolyzed to deoxyribonucleosides according to Nohara et al [15] with minor modifications.…”