Mortality Of Heterotrophic Bacteria Research Articles

Bacterio- and virioplankton in water bodies of a raised bog (Vologda oblast, Russia)

The abundance of virio-and bacterioplankton and the role of viruses in the mortality of heterotrophic bacteria have been studied in three different mire water bodies (lagg, hollow, and stream) in the Shichengskoe raised bog. The abundance of bacteria (up to 93 million cells/mL) and viruses (up to 152 million particles/mL) reached very high values. Considerable differences were found between the mire water bodies in seasonal dynamics and average values of the studied parameters. The ratio of the number of virioplankton to the number of bacterioplankton (median values from 1.3 in a hollow to 5.6 in a stream) is in low ranges of values which are available in literature sources. Viruses did not have a considerable direct effect on bacterioplankton while lysing ≤7.8% of the bacterial production.

Virioplankton in the Kara Sea: The impact of viruses on mortality of heterotrophic bacteria

Studies were conducted in shallow and deepwater areas of the Kara Sea. The abundance of bacteria (NB) and the abundance of viruses (NV) ranged within (19.4–2215.1) × 103 cells/ml and (97.6–5796.8) × 103 particles/ml, respectively. The virus to bacteria ratio varied from 1.4 to 29.1. A positive correlation was found between NB and NV (R = 0.87, n = 45, p = 0.05. Using electron transmission microscopy it was detected that the frequency of visibly infected cells of bacteria (FVIC) varied from 0.2 to 1.9% of NB. The maximum values of FVIC were recorded in the estuary of the Yenisei River. The infected cells of bacteria contained from 4 to 127 (an average of 12) phages/cell of mature viruses. Virus-mediated mortality of bacteria was 0.5% and varied from 1.4 to 16.1% of the total mortality of bacterioplankton. This indicates a minor role of viruses in the control of overabundance and production of bacterioplankton in the Kara Sea during the surveyed period.

Impact of viruses on mortality of heterotrophic bacteria in rivers flowing through a large city (Cherepovets, Upper Volga)

The abundance and production of planktonic viruses, frequency of infected bacterial cells and number of mature phages in infected bacterial cells, and virus-induced mortality of bacterioplankton were studied in two small rivers and the large Sheksna River flowing through a large city in April–October, 2011. High positive correlations have been determined between the abundance of planktonic viruses and bacteria and the number of viruses attached to bacterial cell walls and the frequency of infected bacteria. The number of planktonic viruses and the mortality of bacteria caused by virus-induced lysis in hypertrophic and eutrophic small rivers are higher than in the mesotrophic Sheksna River.

Влияние вирусов на смертность гетеротрофных бактерий в реках, протекающих через большой город (г. Череповец, Верхняя Волга

Влияние вирусов на смертность гетеротрофных бактерий в реках, протекающих через большой город (г. Череповец, Верхняя Волга

Virio- and bacterioplankton of a small river: Influence that viruses have on the mortality of heterotrophic bacteria

The spatial distribution of virio- and bacterioplankton and the role that viruses play in heterotrophic bacteria elimination was studied in the small Il’d’ River (Rybinskoe Reservoir tributary, Upper Volga). The bacterioplankton abundance and biomass constituted 3.3–19.6 (8.5 on average) million cells/ml and 501–2353 mg/m3 (1054 mg/m3 on average), respectively. The highest abundance was registered for the shallow areas under anthropogenic and zoogenic load. The virus abundance varied from 7.4 to 66.9 million particles/ml, being 30.9 million particles/ml on average. The bacteria: virus ratio was in the range of 1.2–11.0 (4.0 on average); the maximal values were registered for the deepest parts of the river. One infected bacterial cell carried up to 45 virile phages. The virus-induced mortality (VIM) was in the range of 1.1–7.8% (3.7% on average) from daily bacterial production. These data evidenced a high abundance of bacterioplankton in the studied river and an insignificant impact of virus-mediated regulation on bacterial abundance and production.

Impact of viruses on heterotrophic bacterioplankton and picocyanobacteria in reservoirs

In aquatic ecosystems, viruses are considered to bean important factor controlling bacterio and phytoplankton abundance, production, and diversity andplay an important role in the biogeochemical cycles ofcarbon and other components [1]. Analysis of literature on ecology of aquatic viruses shows that, atpresent, viruses in freshwaters are less studied than inmarine bodies of water [2]. Despite numerous publications on virioplankton in lakes, only scanty data can befound on virioplankton in reservoirs [3–5]. Thisrestricts our knowledge of the functioning of this widespread group of artificial water objects. We have performed the first study on the quantitative distributionof planktonic viruses and their role in the mortality ofheterotrophic bacteria and picocyanobacteria in reservoirs of the Volga–Baltic Sea basin.The studies were carried out in July–August of theyears 2005 and 2007. Planktonic viral particles werecounted by epifluorescent microscopy using the SYBRGreen 1 fluorochrome and Al

Seasonal variations in abundance, growth and mortality of heterotrophic bacteria in Kagoshima Bay

Seasonal changes in abundance, growth and mortality of heterotrophic bacteria were investigated monthly from collections and dilution experiments in Kagoshima Bay, the southernmost of Japan. Bacteria occurred abundantly with considerable variation in the surface layers where chlorophyll a concentrations were high, whereas seasonal variations were obscure below 100 m. Especially, bacteria showed a decline of cell density toward summer when heterotrophic nano-flagellates increased their abundance. Seasonal and vertical variations in bacterial cell number during the study period were positively correlated with those of water temperature and pico-sized chlorophyll a concentration. Maximum growth and mortality rates showed positive correlations with water temperature but no positive relationships to size-fractionated chlorophyll a. Net increase rate (i.e. in situ rate if abundance changes) was negatively correlated with cell density of heterotrophic nano-flagellates. It is concluded that bacterial abundance is controlled by the resultant (i.e. net growth rate) of the balance between maximum growth and predatory mortality by heterotrophic nano-flagelllates which are both dependent on ambient temperature.

Response of heterotrophic bacteria to the spring phytoplankton bloom in the Oyashio region

Temporal changes in abundance, growth and mortality of heterotrophic bacteria were investigated from frequent dilution experiments in the Oyashio region to evaluate their response to the spring phytoplankton bloom. Bacterial abundance fluctuated from 1.0 to 2.6×10 5 cells mL −1. Cell density was not different between the pre-bloom and bloom periods, and showed no clear temporal pattern. Potential growth ( g′) and mortality ( m) varied from 1.11 to 2.39 day −1 and from 1.21 to 2.16 day −1, respectively. Neither g′ nor m was correlated with water temperature or chlorophyll a. Apparent growth rate in unenriched 100% seawater incubations ( g o ) was not limited by nutrients throughout the study period and was comparable to net growth rate ( g′ −m) estimates from dilution experiments. These results suggest that bacterial abundance is nearly steady-state in the pre-bloom and bloom period, because bacterial growth is nearly nutritionally saturated and balanced with high mortality.

Estimates of bacterial and phytoplankton mortality caused by viral lysis and microzooplankton grazing in a shallow eutrophic lake

Summary1. Since viral lysis and zooplankton grazing differ in their impact on the aquatic food web, it is important to assess the relative importance of both mortality factors. In this study, an adapted version of the dilution technique was applied to simultaneously estimate the impact of both viral lysis and zooplankton grazing on the mortality of heterotrophic bacteria, eukaryotic algae, unicellular cyanobacteria, prochlorophytes and especially filamentous cyanobacteria in a shallow eutrophic lake.2. Four dilution experiments were performed in December 2004, January 2005, and March and April 2006. Viral and heterotrophic bacterial abundances were obtained by epifluorescence microscopy and abundances of different phytoplankton groups by flow cytometry and light microscopy.3. Viral lysis was identified as the main mortality cause during the December 2004 and January 2005 experiments, apparently removing between 84% and 97% of the potential filamentous cyanobacterial production and up to 101% of the potential heterotrophic bacterial production. Microzooplankton grazing was estimated to remove between 90% and 99% of the potential unicellular cyanobacterial production and up to 46% of the potential heterotrophic bacterial production during the spring 2006 experiments.4. In some cases, no significant impact of viral lysis or zooplankton grazing was detected. Contrary to expectations, the apparent growth rate of filamentous cyanobacteria was even sometimes observed to decrease significantly upon dilution of microzooplankton.5. The dilution technique can give valuable insight into the impact of zooplankton grazing and viral lysis on the mortality of different plankton groups but require some caveats require special care to be taken when comparing and interpreting results.

Distribution of viruses and their impact on bacterioplankton in mesotrophic and eutrophic reservoirs

Spatial distribution of planktonic viral particles (virioplankton) and mortality of heterotrophic bacteria caused by viral lysis were studied in the eutrophic Ivan’kovskoe and mesotrophic Uglichskoe reservoirs (the Upper Volga). During the summer peak of phytoplankton, the number of viral particles was higher in the Ivan’kovskoe Reservoir ((55.1 ± 9.5) × 106 ml−1 on average) than in the Uglichskoe Reservoir ((42.9 ± 5.1) × 106 ml−1 on average). The ratio of viral to bacterial abundances ranged from 2.5 to 7.0. The average number of mature phages in infected heterotrophic bacteria varied from 17 to 109 particles/cell. Most of the infected bacterial cells in the Ivan’kovskoe Reservoir were rod-shaped, and, in the Uglichskoe Reservoir, they were mainly vibrio-shaped. In the Ivan’kovskoe Reservoir, from 8.3 to 22.4% of planktonic bacteria were infected by phages, suggesting phage-induced mortality of bacterioplankton equal to 10.5–34.8% (19.1% on average) of the daily bacterial production. In the Uglichskoe Reservoir, from 9.4 to 33.5% of bacteria were phage-infected, suggesting phage-induced bacterial mortality of 13.7–40.2% (23.5% on average) of the daily bacterial production. The obtained results testify to an important role of autochthonous viruses in the regulation of bacterioplankton abundance and production in the reservoirs.

Estimates of protozoan‐ and viral‐mediated mortality of bacterioplankton in Lake Bourget (France)

Summary1. We performed three, 1‐week in situ experiments in March‐April (expt 1), May (expt 2) and August (expt 3) 2003 in order to assess protozoan and virus‐induced mortality of heterotrophic bacteria in a French lake. Viral and bacterial abundances were obtained using flow cytometry (FCM) while protozoa were counted using epifluorescence microscopy (EFM).2. A dilution approach, applied to pretreated grazer‐free samples, allowed us to estimate that viral lysis could be responsible for 60% (expt 1), 35% (expt 2) and 52% (expt 3) of daily heterotrophic bacterial mortality. Flagellate (both mixotrophic and heterotrophic) grazing in untreated samples, was responsible for 56% (expt 1), 63% (expt 2) and 18% (expt 3) of daily heterotrophic bacteria removal.3. These results therefore suggest that both viral lysis and flagellate grazing had a strong impact on bacterial mortality, and this impact varied seasonally.4. From parallel transmission electron microscopy (TEM) analysis, we found that the burst size (i.e. the number of viruses potentially released per lysed cell) ranged from nine to 25 (expt 1), 10 to 35 (expt 2) and eight to 25 (expt 3). The percentage of infected heterotrophic bacteria was 5.7% (expt 1), 3.4% (expt 2) and 5.7% (expt 3) so that the calculated percentage of bacterial mortality induced by viruses was 6.3% (expt 1), 3.7% (expt 2) and 6.3% (expt 3).5. It is clear that the dilution‐FCM and TEM methods yielded different estimates of viral impact, although both methods revealed an increased impact of viruses during summer.