Carbon and Nitrogen Content of Natural Planktonic Bacteria

A method of estimating carbon and nitrogen content per unit of natural bacterial cell volume was developed. This method is based on the difference in the retentiveness of bacteria between two kinds of glass fiber filter, GF/C and GF/F (Whatman, Inc., Clifton, N.J.). Biovolume and biomass (carbon and nitrogen content) of bacteria which passed through the GF/C but not the GF/F filter were estimated with an epifluorescence microscopy and a CHN analyzer, respectively. From seasonal determinations of natural planktonic bacteria in epilimnetic waters of a mesotrophic lake, the conversion factors of 106 fg of C/μm³ and 25 fg of N/μm³ were derived as average values. By using these values, the contribution of bacteria to the biomass of lake plankton is discussed.     

Planktonic Luminous Bacteria of Vellar Estuary,South India

Distribution of planktonic luminous bacteria in relation to environmental parameters was investigated at two stations located in the Vellar Estuary. Luminous microflora showed a pronounced seasonal cycle with very low counts during monsoon months followed by an increase in post monsoon and peak counts during summer. The population density of these procaryotes was remarkably high ranging from 3.5 to 33.1 colony forming units per ml. They constituted 2.1 to 52.1 % of the total bacterial counts. Salinity appeared to govern the distribution of luminous procaryotes as their counts corresponded well with fluctuations in salinity. Taxonomic affiliation of the isolates revealed predominance of Vibrio harveyi. Vibrio fischeri and Photobacterium leiognathi exhibited sparse distribution.     

Long Lag Times and High Velocities in the Motility of Natural Assemblages of Marine Bacteria

The motility characteristics of natural assemblages of coastal marine bacteria were examined. Initially, less than 10% of the bacteria were motile. A single addition of tryptic soy broth caused an increase in the motile fraction of cells but only after 7 to 12 h. Motility peaked at 15 to 30 h, when more than 80% of cells were motile. These results support the proposal that energy limits motility in the marine environment. Cell speeds changed more than an order of magnitude on timescales of milliseconds and hours. The maximum community speed was 144 (mu)m s(sup-1), and the maximum individual burst velocity was 407 (mu)m s(sup-1). In uniform medium, speed was an inverse function of tryptic soy broth concentration, declining linearly over 0.001 to 1.0%. In media where concentration gradients existed, the mean speed was a function of position in a spatial gradient, changing from 69 to 144 (mu)m s(sup-1) over as little as 15 to 30 (mu)m. The results suggest that marine bacteria are capable of previously undescribed quick shifts in speed that may permit the bacteria to rapidly detect and keep up with positional changes in small nutrient sources. These high speeds and quick shifts may reflect the requirements for useful motility in a turbulent ocean.     

Patchiness in the Distribution of Planktonic Heterotrophic Bacteria in Lakes

By using conventional dilution plating procedures, the heterotrophic planktonic bacteria in Lake Washington were found to be distributed in small-scale (<1.0 ml) and large-scale (>1 m in horizontal distance) patches. Recommendations are made on sampling and enumeration procedures to minimize the effect of patchiness on obtaining an accurate estimate of bacterial numbers.     

Comparative Genomics of DNA Fragments from Six Antarctic Marine Planktonic Bacteria

Six environmental fosmid clones from Antarctic coastal water bacterioplankton were completely sequenced. The genome fragments harbored small-subunit rRNA genes that were between 85 and 91% similar to those of their nearest cultivated relatives. The six fragments span four phyla, including the Gemmatimonadetes, Proteobacteria (α and γ), Bacteroidetes, and high-G+C gram-positive bacteria. Gene-finding and annotation analyses identified 244 total open reading frames. Amino acid comparisons of 123 and 113 Antarctic bacterial amino acid sequences to mesophilic homologs from G+C-specific and SwissProt/UniProt databases, respectively, revealed widespread adaptation to the cold. The most significant changes in these Antarctic bacterial protein sequences included a reduction in salt-bridge-forming residues such as arginine, glutamic acid, and aspartic acid, reduced proline contents, and a reduction in stabilizing hydrophobic clusters. Stretches of disordered amino acids were significantly longer in the Antarctic sequences than in the mesophilic sequences. These characteristics were not specific to any one phylum, COG role category, or G+C content and imply that underlying genotypic and biochemical adaptations to the cold are inherent to life in the permanently subzero Antarctic waters.     

Dynamics of Microbial Communities on Marine Snow Aggregates: Colonization, Growth, Detachment, and Grazing Mortality of Attached Bacteria

We studied the dynamics of microbial communities attached to model aggregates (4-mm-diameter agar spheres) and the component processes of colonization, detachment, growth, and grazing mortality. Agar spheres incubated in raw seawater were rapidly colonized by bacteria, followed by flagellates and ciliates. Colonization can be described as a diffusion process, and encounter volume rates were estimated at about 0.01 and 0.1 cm³ h⁻¹ for bacteria and flagellates, respectively. After initial colonization, the abundances of flagellates and ciliates remained approximately constant at 10³ to 10⁴ and ~10² cells sphere⁻¹, respectively, whereas bacterial populations increased at a declining rate to >10⁷ cells sphere⁻¹. Attached microorganisms initially detached at high specific rates of ~10⁻² min⁻¹, but the bacteria gradually became irreversibly attached to the spheres. Bacterial growth (0 to 2 day⁻¹) was density dependent and declined hyperbolically when cell density exceeded a threshold. Bacterivorous flagellates grazed on the sphere surface at an average saturated rate of 15 bacteria flagellate⁻¹ h⁻¹. At low bacterial densities, the flagellate surface clearance rate was ~5 × 10⁻⁷ cm² min⁻¹, but it declined hyperbolically with increasing bacterial density. Using the experimentally estimated process rates and integrating the component processes in a simple model reproduces the main features of the observed microbial population dynamics. Differences between observed and predicted population dynamics suggest, however, that other factors, e.g., antagonistic interactions between bacteria, are of importance in shaping marine snow microbial communities.     

Production and Turnover of Planktonic Bacteria in Two Southeastern Blackwater Rivers

Production by attached and free-living planktonic bacteria in two blackwater rivers in the Southeastern United States was measured over a period of 14 months by using the rate of incorporation of [methyl-³H]thymidine into DNA. Production rates and biomass dynamics were compared to determine the potential for in situ production to supply planktonic biomass. Bacterial production in these rivers was moderate and varied seasonally. Rates varied from 0.058 to 2.120 mg of C m⁻³ h⁻¹ in the Ogeechee River and from 0.002 to 2.418 mg of C m⁻³ h⁻¹ in Black Creek. Regressions of growth rate on various environmental variables showed that temperature and total dissolved organic carbon concentration were the best predictors of growth. Although attached bacteria were <21% of the total biomass, they accounted for up to 53% of the total production. Turnover times for attached bacteria ranged from <1 day to >3 years depending on season. Turnover times of free-living bacteria varied from 4.4 days to 11.8 years. Comparisons of biomass with production indicated that during most seasons, the majority of bacterial biomass in these rivers was of allochthonous origin. During summer, when water temperatures were high, bacterial growth in the river may have supplied a greater percentage of the standing stock of bacteria than allochthonous inputs.     

Planktonic Marine Luminous Bacteria: Species Distribution in the Water Column

Luminous bacteria were isolated from oceanic water samples taken throughout the upper 1,000 m and ranged in density from 0.4 to 30 colony-forming units per 100 ml. Generally, two peaks in abundance were detected: one in the upper 100 m of the water column, which consisted primarily of Beneckea spp.; and a second between 250 and 1,000 m, which consisted almost entirely of Photobacterium phosphoreum. The population of P. phosphoreum remained relatively stable in abundance at one station that was visited three times over a period of 6 months. However, the abundance of luminous Beneckea spp. isolated from the upper waters fluctuated considerably; they were, as high as 30 colony-forming units per 100 ml in the spring and were not detected in the winter. Water samples from depths of 4,000 to 7,000 m contained less than 0.1 luminous colony-forming unit per 100 ml. The apparent vertical stratification of two taxa of oceanic luminous bacteria may reflect not only differences in physiology, but also depth-related, species-specific symbiotic associations.     

Malaria Prevention with IPTp during Pregnancy Reduces Neonatal Mortality

Background

In the global context of a reduction of under-five mortality, neonatal mortality is an increasingly relevant component of this mortality. Malaria in pregnancy may affect neonatal survival, though no strong evidence exists to support this association.

Methods

In the context of a randomised, placebo-controlled trial of intermittent preventive treatment (IPTp) with sulphadoxine-pyrimethamine (SP) in 1030 Mozambican pregnant women, 997 newborns were followed up until 12 months of age. There were 500 live borns to women who received placebo and 497 to those who received SP.

Findings

There were 58 infant deaths; 60.4% occurred in children born to women who received placebo and 39.6% to women who received IPTp (p = 0.136). There were 25 neonatal deaths; 72% occurred in the placebo group and 28% in the IPTp group (p = 0.041). Of the 20 deaths that occurred in the first week of life, 75% were babies born to women in the placebo group and 25% to those in the IPTp group (p = 0.039). IPTp reduced neonatal mortality by 61.3% (95% CI 7.4%, 83.8%); p = 0.024].

Conclusions

Malaria prevention with SP in pregnancy can reduce neonatal mortality. Mechanisms associated with increased malaria infection at the end of pregnancy may explain the excess mortality in the malaria less protected group. Alternatively, SP may have reduced the risk of neonatal infections. These findings are of relevance to promote the implementation of IPTp with SP, and provide insights into the understanding of the pathophysiological mechanisms through which maternal malaria affects fetal and neonatal health.

Trial Registration

ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT00209781","term_id":"NCT00209781"}}NCT00209781     

Herbivores and the Spatial Distributions of the Phytoplankton. II. Estimating Grazing in Planktonic Environments

Large errors are made when laboratory measurements of the ingestion rate of herbivorous zoo-plankton are used to estimate grazing in planktonic environments. The errors arise because the spatial heterogeneity in natural plankton distributions is greater than the heterogeneity present in laboratory experiments. Two probability models are developed for extrapolating laboratory measurements of ingestion to planktonic environments. Both models require sample statistics of the plankton distributions, and these are estimated from sampling studies of the small scale distribution of marine plankton. One model predicts laboratory measurements overestimate the ration obtained by an individual copepod by 30 %. A second model predicts errors exceeding ±50 % are possible when laboratory measurements are used to estimate the grazing by a population of cope-pods.     

Diversity of Planktonic Bacteria in Durgun and Taishir Reservoirs (Western Mongolia)

Microbiology - This is the first report on the application of high-throughput sequencing of the 16S rRNA gene fragments for investigation of bacterioplankton diversity in two largest and relatively...     

Growth and Grazing Rates of the Marine Planktonic Ciliate Strombidinopsis sp. on Red-Tide and Toxic Dinoflagellates

ABSTRACT We investigated growth and grazing rates of Strombidinopsis sp. when feeding on several species of red-tide and/or toxic dinoflagellates. Strombidinopsis sp. one of the largest aloricate choreotrichs so far reported, grew well on Lingulodinium polyedrum, Gymnodinium sanguineum, Scrippsiella trochoidea, Cochlodinium polykrikoides , and Prorocentrum minimum , but failed to grow on Amphidinium carterae. Specific growth rates of Strombidinopsis sp. increased rapidly with increasing prey density up to ca. 100 ng C ml^-1, but were saturated or increased slightly at higher concentrations. Maximum specific growth rates of Strombidinopsis sp. on various prey species were 1.38 day^-1 for C. polykrikoides , 1.27 for G. sanguineum , 1.06 for P. minimum , 0.83 for L. polyedrum , and 0.67 for S. trochoidea. Threshold prey concentrations (where net growth = 0) were 12–38 ng C ml^-1. Maximum ingestion and clearance rates of Strombidinopsis sp. were 353 ng C grazer^-1 day^-1 and 110 μ, l grazer^-1 h^-1, respectively. Strombidinopsis sp. exhibited higher maximum growth, ingestion, and clearance rates than the mixotrophic dinoflagellate Fragilidium cf. mexicanum or the heterotrophic dinoflagellates Protoperidinium cf. divergens and P. crassipes , when grown on the same prey species. In addition, the sequence of prey species arranged according to growth response of Strombidinopsis sp. differed considerably from those of Fragilidium cf. mexicanum, Protoperidinium cf. divergens , and P. crassipes.     

Use of Hoechst Dyes 33258 and 33342 for Enumeration of Attached and Planktonic Bacteria

The DNA-specific fluorochromes Hoechst 33258 and 33342 were used to enumerate aquatic bacteria by epifluorescent direct counts. Cultures of estuarine bacteria gave identical counts when stained with Hoechst 33258 or acridine orange, whereas natural populations of aquatic bacteria gave 92 to 98.5% of the acridine orange counts. The technique had distinct advantages over acridine orange when enumerating bacteria on surfaces which bind acridine orange, such as polystyrene.     

How the Motility Pattern of Bacteria Affects Their Dispersal and Chemotaxis

Most bacteria at certain stages of their life cycle are able to move actively; they can swim in a liquid or crawl on various surfaces. A typical path of the moving cell often resembles the trajectory of a random walk. However, bacteria are capable of modifying their apparently random motion in response to changing environmental conditions. As a result, bacteria can migrate towards the source of nutrients or away from harmful chemicals. Surprisingly, many bacterial species that were studied have several distinct motility patterns, which can be theoretically modeled by a unifying random walk approach. We use this approach to quantify the process of cell dispersal in a homogeneous environment and show how the bacterial drift velocity towards the source of attracting chemicals is affected by the motility pattern of the bacteria. Our results open up the possibility of accessing additional information about the intrinsic response of the cells using macroscopic observations of bacteria moving in inhomogeneous environments.     

Contrasting Community versus Population-Based Estimates of Grazing and Virus-Induced Mortality of Phytoplankton

In this study, grazing and virus-induced mortality of phytoplankton was investigated in a freshwater pond at the University of Toronto Mississauga, Canada, during September 2009. The modified dilution assay, which partitions phytoplankton mortality into virus and grazing-induced fractions, was used along with newly designed, taxon-specific quantitative polymerase chain reaction (qPCR) assays that target psbA gene fragments to estimate growth and mortality rates for both the entire phytoplankton community and four distinct phytoplankton populations. Community mortality was estimated via fluorometric determination of chlorophyll a (Chl a) concentrations, whereas the relative mortality of individual phytoplankton populations was estimated via qPCR. The sources and amounts of mortality for individual phytoplankton populations differed from those of the whole community, as well as from each other. Grazing was found to be the only significant source of mortality for the community (0.32 day(-1)), and the Prymnesiales (1.65 day(-1)) and Chroococcales (2.79 day(-1)) populations studied. On the other hand, the Chlamydomonadales population examined experienced both significant grazing (1.01 day(-1)) and viral lysis (0.96 day(-1)), while the Chlorellales population only experienced significant mortality as a result of viral lysis (1.38 day(-1)). Our results demonstrate that the combination of qPCR and the modified dilution method can be used to estimate both viral lysis and grazing pressure on several individual phytoplankton populations within a community simultaneously. Further, previously noted limitations of the modified dilution method associated with the dilution of specific phytoplankton populations at low abundances can be overcome with the qPCR-based approach. Most importantly, this study demonstrates that when used alone, whole community-based methods of assessing mortality can overlook valuable information about carbon flow in aquatic microbial food webs.     

Influence of Cyanobacterial Hyperscum on Heterotrophic Activity of Planktonic Bacteria in a Hypertrophic Lake

The response of the planktonic heterotrophic bacterial community to the buildup and breakdown of a semipermanent, crusted, floating cyanobacterial mat, or hyperscum, that covered 1 to 2 ha was studied in a hypertrophic lake (Hartbeespoort Dam, South Africa). The initial response of bacteria in the main basin to the release of dissolved organic carbon (DOC) from the hyperscum 1 km away was an increase in activity per cell from 35 × 10⁻¹² to 153 × 10⁻¹² μg of C cell⁻¹ h⁻¹ for total cell counts, while activity per cell for metabolically active cells increased from 19 × 10⁻¹¹ to 85 × 10⁻¹¹ μg of C cell⁻¹ h⁻¹. No major population growth occurred at this stage. Later, with the continuous supply of DOC from the hyperscum, total bacterial numbers increased from 6.6 × 10⁶ to 20 × 10⁶ cells ml⁻¹, while the activity per cell declined. Metabolically active bacteria followed the same trend. Shorter-term DOC increases caused only increases in bacterial activity per cell. The data from Hartbeespoort Dam demonstrate an interesting and little-documented mechanism by which aquatic bacteria respond to increased DOC concentration and which may be universal for aquatic systems.     

Production Rate of Planktonic Bacteria in the North Basin of Lake Biwa, Japan

Vertical and seasonal variations in the cell number and production rate of planktonic bacteria were investigated at a pelagic site (water depth, ca. 72 m) of the north basin of Lake Biwa during April to October 1986. The [methyl-³H]thymidine uptake rate into a cold trichloroacetic acid-insoluble fraction and the frequency of dividing cells (FDCs) were measured for each sample as indices of the bacterial production rate. The seasonal data of bacterial number, thymidine uptake rate, and bacterial growth rate based on the FDCs were correlated with one another (rank correlation analysis, P < 0.05). These bacterial variables were not correlated positively with the chlorophyll a concentration. Vertically, the maxima of both bacterial number and the thymidine uptake rate were found in the euphotic zone. The direct counting of bacteria and the measurements of thymidine uptake rate combined with the size-fractionation method revealed that more than 90% of the bacterial biomass and production rate were attributed to unattached bacteria throughout the investigation period. The carbon flux estimates of bacterial production were less certain due to the variability of the conversion factor for the thymidine uptake method and that of the calibration for the FDC method, but even when the conservative range of bacterial net production rate was used (5 to 60 μg of carbon per liter per day), it can be suggested that bacterial net production in the investigated area was a significant fraction (ca. 30%) of the level of the primary production rate in the same water basin.     

北京市五大水系水体浮游细菌的数量特征研究

为掌握水域浮游细菌数量分布特征及其变化情况,采用荧光显微镜细菌计数法（AODC）于2016年6月至2018年9月研究了北京市五大水系浮游细菌的数量特征。结果表明,各水系浮游细菌密度分别为潮白河水系（0.24～28.46）×104 cell/mL,大清河水系（1.34～64.00）×10⁴ cell/mL,永定河水系（0.17～6.77）×10⁴ cell/mL,北运河水系（0.24～64.00）×10⁴ cell/mL,蓟运河水系（0.80～112.00）×10⁴ cell/mL。SPSS相关分析表明,各水系浮游细菌密度与水体理化因子间的相关性存在明显差异,大清河水系细菌密度与TN（P<0.05）呈显著正相关,与TP（P<0.01）和ADP(P<0.01)呈极显著正相关;永定河水系细菌密度与TAN（P<0.05）和TP(P<0.05)呈显著正相关,与ADP（P<0.01）呈极显著正相关;蓟运河水系细菌密度与Chl-a（P<0.05）呈显著正相关;潮白河水系及北运河水系细菌密度则与各理化因子均无显著相关性。从浮游细菌数量来看,各水系水质均较好,其中永定河水系水质最优。