Decomposition of Phragmites australis rhizome in a shallow lake

Decomposition of Phragmites australis (Cav. Trin ex Steudel) rhizome was studied at Lake Fertő/Neusiedler See using the litter bag technique. Samples were analysed for rhizome dry mass, fibre (cellulose, hemicellulose, lignin) and nutrient content (C, N, P and S), litter-associated fungal biomass, potential microbial respiration (electron transport activity: ETS) and cellulolitic bacteria. The mass loss of decomposing rhizome was rapid in the initial period and only 13.6% of the dry mass remained at the end of the experiment during 953 days. Substantial quantities of C, N, S and P were lost during 99 days; only 18% C, 19% N, 14% S and 6.4% of the P remained after 953 days. Hemicellulose degraded more rapidly than the other fibres whilst the lignin had the slowest rate of decomposition. Bacteria were found to be the primary colonizers of plant detritus, which was followed by fungal growth. An antagonistic relationship was observed between bacteria and fungi. Fungal biomass as determined by ergosterol concentrations ranged between 4.1 and 420 μg g⁻¹ and peaked every year in September. The number of cellulolitic bacteria varied from 0 to 22 MPN g⁻¹ with higher values in summer. The ETS-activity ranged between 0.1 and 1.6 mg O₂ g⁻¹ h⁻¹. The changes in ETS-activity varied almost in parallel with the in situ temperature of the lake water.     

Complex interactions and different possible pathways among functional components of the aquatic microbial world in Farasan Archipelago,Southern Red Sea,Saudi Arabia

This work aims to outline the dynamics of trophic links between the three main microbial components (bacteria, nanoflagellates, and ciliates) of the Farasan Archipelago in order to establish a baseline for future research in this area. The Farasan Archipelago lies along the southwestern coast of the Saudi Arabia, southern Red Sea between 16°20′–17°10′N and 41°30′–42°30′E and had been declared as marine and terrestrial reserve by the year 1996. Three different sites were chosen for this study, with each site visited bimonthly for 18 months from September 2016 to February 2018. Bacteria, nanoflagellates and ciliates were enumerated in order to explore the complex interactions between the main microbial categories in sea waters of the Farasan Archipelago. High abundances were recorded during the present study for bacteria (8.7 × 10⁶ bacteria ml⁻¹), nanoflagellates (3.7 × 10⁴ TNAN ml⁻¹) and ciliates (40.4 ciliates ml⁻¹). The paper discusses the various potential pathways controlling the complex interactions between these microbial groups in this part of the southern Red Sea. It is concluded that a linear trophic chain consisting of bacteria; heterotrophic nanoflagellates; filter feeding ciliates is a major route by which the production of bacteria is transferred to the higher consuming levels, thereby confirming the high importance of t bottom-up control (food supply), alongside top-down control (predation) in regulating bacterial abundances in the Farasan Archipelago. During the present investigation, each nanoflagellate ingested between 11 and 87 bacteria in one hour, while each ciliate consumed between 20 and 185 nanoflagellates every hour. These calculated grazing rates of protistan eukaryotes confirmed the role of heterotrophic nanoflagellates as the main consumers of bacteria, and the role of ciliates as the major control for the heterotrophic nanoflagellate population dynamics, and thus the top predators within the microbial plankton assemblage in the Farasan Archipelago.     

Algicidal and growth-inhibiting bacteria associated with seagrass and macroalgae beds in Puget Sound,WA, USA

The algicidal and growth-inhibiting bacteria associated with seagrasses and macroalgae were characterized during the summer of 2012 and 2013 throughout Puget Sound, WA, USA. In 2012, Heterosigma akashiwo-killing bacteria were observed in concentrations of 2.8 × 10⁶ CFU g⁻¹ wet in the outer organic layer (biofilm) on the common eelgrass (Zostera marina) in north Padilla Bay. Bacteria that inhibited the growth of Alexandrium tamarense were detected within the biofilm formed on the eelgrass canopy at Dumas Bay and North Bay at densities of ∼10⁸ CFU g⁻¹ wet weight. Additionally, up to 4100 CFU mL⁻¹ of algicidal and growth-inhibiting bacteria affecting both A. tamarense and H. akashiwo were detected in seawater adjacent to seven different eelgrass beds. In 2013, H. akashiwo-killing bacteria were found on Z. marina and Ulva lactuca with the highest densities of ∼10⁸ CFU g⁻¹ wet weight at Shallow Bay, Sucia Island. Bacteria that inhibited the growth of H. akashiwo and A. tamarense were also detected on Z. marina and Z. japonica at central Padilla Bay. Heterosigma akashiwo cysts were detected at a concentration of 3400 cysts g⁻¹ wet weight in the sediment from Westcott Bay (northern San Juan Island), a location where eelgrass disappeared in 2002. These findings provide new insights on the ecology of algicidal and growth-inhibiting bacteria, and suggest that seagrass and macroalgae provide an environment that may influence the abundance of harmful algae in this region. This work highlights the importance of protection and restoration of native seagrasses and macroalgae in nearshore environments, in particular those regions where shellfish restoration initiatives are in place to satisfy a growing demand for seafood.     

Improvement of a synthetic medium for Dictyostelium discoideum

Dictyostelium discoideum is of considerable interest as an expression system for the production of proteins of high value. The cultivation of this social amoeba is not as easy as that of other common microbial expression systems. Wildtype strains grow on bacteria. Mutant strains growing on axenic media reach cell densities of 1–2×10⁷ ml⁻¹ when cultivated in commonly used complex media. A totally synthetic medium formulated by Franke and Kessin (Proc. Natl. Acad. Sci. USA 74 (1977) 2157) has become popular and allows cell densities of about 3×10⁷ ml⁻¹ to be obtained. This medium (FM) is being improved mainly on the basis of the analysis of limitations with respect to amino acids. With this improved synthetic medium (SIH) cell densities in the order of 5–6×10⁷ ml⁻¹ have been achieved.     

Study of different nitrogen sources on glucose uptake and production of melanin precursors and fungal mass of Fonsecaea pedrosoi cultured in tricyclazole

The influence of tricyclazole on the production of phenolic precursors, glucose uptake and production of fungal mass of Fonsecaea pedrosoi was assessed in the presence of phenylalanine, sodium nitrate and tryptophan. Photocolorimetry was used for the quantitation of glucose and total phenol, and the dry weight method for biomass. The glucose uptake with phenylalanine was 99.85×10³ mg/ml; with tryptophan, 99.88×10³ mg/ml and with sodium nitrate, 99.90×10³ mg/ml. Production of biomass: with tryptophan, 2.7×10⁻¹ mg; with sodium nitrate, 3.0×10⁻¹ mg and with phenylalanine, 3.4×10⁻¹ mg. Tricyclazole induced higher phenol accumulation, lower glucose uptake, inhibition of melanin deposition on the cell and higher production and higher biomass production in relation to glucose uptake for all nitrogen sources tested under these conditions. A negative correlation between biomass production and glucose uptake was observed in the presence of secondary metabolism.     

Decomposition of Phragmites australis rhizome in a shallow lake

Decomposition of Phragmites australis (Cav. Trin ex Steudel) rhizome was studied at Lake Fert?/Neusiedler See using the litter bag technique. Samples were analysed for rhizome dry mass, fibre (cellulose, hemicellulose, lignin) and nutrient content (C, N, P and S), litter-associated fungal biomass, potential microbial respiration (electron transport activity: ETS) and cellulolitic bacteria. The mass loss of decomposing rhizome was rapid in the initial period and only 13.6% of the dry mass remained at the end of the experiment during 953 days. Substantial quantities of C, N, S and P were lost during 99 days; only 18% C, 19% N, 14% S and 6.4% of the P remained after 953 days. Hemicellulose degraded more rapidly than the other fibres whilst the lignin had the slowest rate of decomposition. Bacteria were found to be the primary colonizers of plant detritus, which was followed by fungal growth. An antagonistic relationship was observed between bacteria and fungi. Fungal biomass as determined by ergosterol concentrations ranged between 4.1 and 420 μg g⁻¹ and peaked every year in September. The number of cellulolitic bacteria varied from 0 to 22 MPN g⁻¹ with higher values in summer. The ETS-activity ranged between 0.1 and 1.6 mg O₂ g⁻¹ h⁻¹. The changes in ETS-activity varied almost in parallel with the in situ temperature of the lake water.     

Algae,bacteria and detritus as food for the harpacticoid copepod, Heteropsyllus pseudonunni Coull and Palmer

The harpacticoid copepod, Heteropsyllus pseudonunni Coull and Palmer, when fed Juncus roemerianus Scheele (needlerush) detritus produced significantly more eggs than when fed the alga Dunaliella sp. Five food rations and a starved control were used: A, algal concentration ≈ 10⁴ cells · ml^?1; LA, algal concentration 10³ cells · ml^?1; D, detritus concentration 0.25 g · ml^?1; LD, detritus concentration 0.025 g · ml^?1; LDLA, a mixture of the LD and LA rations. Geometric mean total egg production values were: LDLA 132.5; LD 132.6; D 120.5; A 65.8; LA 5.0. The LA results were significantly less (P = 0.05; Student-Newman-Keuls' test) than all others, while the A results were significantly less than the LDLA, LD and D results. The LDLA, LD and D results were not statistically different. Similar trends were obtained when mean brood sizes and mean number of broods were compared. In a second feeding experiment, using Juncus detritus, bacteria on sand grains, and algae (Nitzschia sp.) on sand grains, Heteropsyllus pseudonunni produced significantly more eggs (P = 0.05; SNK test) when fed detritus (166.0) or bacteria (132.2) than algae (58.9). The detritus and bacteria results were not significantly different.     

Sea Ice Microbial Communities: Distribution, Abundance, and Diversity of Ice Bacteria in McMurdo Sound, Antarctica, in 1980

An abundant and diverse bacterial community was found within brine channels of annual sea ice and at the ice-seawater interface in McMurdo Sound, Antarctica, in 1980. The mean bacterial standing crop was 1.4 × 10¹¹ cells m⁻² (9.8 mg of C m⁻²); bacterial concentrations as high as 1.02 × 10¹² cells m⁻³ were observed in ice core melt water. Vertical profiles of ice cores 1.3 to 2.5 m long showed that 47% of the bacterial numbers and 93% of the bacterial biomass were located in the bottom 20 cm of sea ice. Ice bacterial biomass concentration was more than 10 times higher than bacterioplankton from the water column. Scanning electron micrographs showed a variety of morphologically distinct cell types, including coccoid, rod, fusiform, filamentous, and prosthecate forms; dividing cells were commonly observed. Approximately 70% of the ice bacteria were free-living, whereas 30% were attached to either living algal cells or detritus. Interactions between ice bacteria and microalgae were suggested by a positive correlation between bacterial numbers and chlorophyll a content of the ice. Scanning and transmission electron microscopy revealed a close physical association between epibacteria and a dominant ice alga of the genus Amphiprora. We propose that sea ice microbial communities are not only sources of primary production but also sources of secondary microbial production in polar ecosystems. Furthermore, we propose that a detrital food web may be associated with polar sea ice.     

Seasonal variation of nutrients,organic carbon,ATP, and microbial standing crops in a vertical profile of Pyramid Lake,Nevada

Previous studies of Pyramid Lake, Nevada, led to the hypothesis that detritus could be an important food source for zooplankton because abundance of palatable algal species did not seem to be enough to support the zooplankton community throughout the year. Furthermore, a large portion of the annual primary productivity was attributed to a nonpalatable blue-green alga, Nodularia spumigena. We felt this alga became important to the Pyramid Lake aquatic community upon death, as edible detritus and a source of new nitrogen. Changes in pelagic detritus concentrations and microbial standing crops were monitored to determine the availability of these potential foods. Epilimnetic particulate organic carbon (POC) was primarily living phytoplankton. During holomixis and following spring primary production, hypolimnetic POC was 60–97% detrital, but these profundal POC concentrations were low (ca 650 µg l^-1). Detritus-bacteria aggregates were observed only following the September cyanophyte bloom. Although pelagic detritus availability for zooplankton was low, bacterial populations were sufficient to be at least a supplemental food source. Bacteria numbers ranged from 0.50 10⁶ to 24.7 10⁶ ml^-1 and increased in response to photosynthetic peaks. Microbial diversity, contribution to POC, and particle association were notable after July. The percentage of living carbon (assessed with ATP measurements) attributable to bacteria was highest in late summer and fall hypolimnetic samples. Patterns of change in organic phosphorus and nitrogen, the presence of a nitrogen-fixing cyanophyte, the N:P ratio, and results of other research demonstrated that non-nitrogen-fixing algae of Pyramid Lake are limited by inorganic nitrogen. The importance of N. spumigena to the aquatic community appeared to be as a source of new nitrogen, rather than as a forage; its mineralization is critical for the growth of palatable diatoms and green algae following winter mixing.     

Distribution and Composition of Microbial Populations in a Landfill Leachate Contaminated Aquifer (Grindsted, Denmark)

Abstract To investigate whether landfill leachates affected the microbial biomass and/or community composition of the extant microbiota, 37 samples were collected along a 305-m transect of a shallow landfill-leachate polluted aquifer. The samples were analyzed for total numbers of bacteria by use of the acridine orange direct count method (AODC). Numbers of dominant, specific groups of bacteria and total numbers of protozoa were measured by use of the most probable number method (MPN). Viable biomass estimates were obtained from measures of ATP and ester-linked phospholipid fatty acid (PLFA) concentrations. The estimated numbers of total bacteria by direct counts were relatively constant throughout the aquifer, ranging from a low of 4.8 × 10⁶ cells/g dry weight (dw) to a high of 5.3 × 10⁷ cells/g dw. Viable biomass estimates based on PLFA concentrations were one to three orders of magnitude lower with the greatest concentrations (up to 4 × 10⁵ cells/g dw) occurring at the border of the landfill and in samples collected from thin lenses of clay and silt with sand streaks. Cell number estimates based on ATP concentrations were also found to be lower than the direct count measurements (<2.2 × 10⁶ cells/g dw), and with the greatest concentrations close to the landfill. Methanogens (Archaea) and reducers of sulfate, iron, manganese, and nitrate were all observed in the aquifer. Methanogens were found to be restricted to the most polluted and reduced part of the aquifer at a maximum cell number of 5.4 × 10⁴ cells/g dw. Populations of sulfate reducers decreased with an increase in horizontal distance from the landfill ranging from a high of 9.0 × 10³ cells/g dw to a low of 6 cells/g dw. Iron, manganese, and nitrate reducers were detected throughout the leachate plume all at maximum cell numbers of 10⁶ cells/g dw. Changes in PLFA profiles indicated that a shift in microbial community composition occurred with increasing horizontal distance from the landfill. The types and patterns of lipid biomarkers suggested that increased proportions of sulfate- and iron-reducing bacteria as well as certain microeukaryotes existed at the border of the landfill. The presence of these lipid biomarkers correlated with the MPN results. There was, however, no significant correlation between the abundances of the specific PLFA biomarkers and quantitative measurements of redox processes. The application of AODC, MPN, PLFA, and ATP analyses in the characterization of the extant microbiota within the Grindsted aquifer revealed that as distance increased from the leachate source, viable biomass decreased and community composition shifted. These results led to the conclusion that the landfill leachate induced an increase in microbial cell numbers by altering the subsurface aquifer so that it was conducive to the growth of methanogens and of iron-and sulfate-reducing bacteria and fungi. Received: 11 June 1998; Accepted: 10 December 1998     

Seasonal development of bacterioplankton in two forest lakes in central Sweden

Bacteria were counted with acridine orange epifluorescence technique in two humic lakes during 3 years. Less than 1% of the cells were found attached to detritus aggregates. 73% of the total number and 48% of the total volume were smaller than 1 µm. The mean cell volume ranged from 0.10 to 0.35 µm³ with the highest cell volumes occurring during early summer contemporarily with the growth of the bacterial biomass and probably indicating favourable growth conditions. The mean density of bacteria in oligotrophic brown-water lakes is higher than in oligotrophic clear-water lakes. The development of bacterial biomass showed a regular and seasonally dependent pattern with maxima during early summer and autumn. The importance of different factors for the regulation of bacterial biomass is discussed. Three different approaches were used to estimate bacterial production. These resulted in an average production rate of 15–60 µg C · l^?1 · d^?1 during the growing season. It was concluded that allochthonous sources comprised a significant part of the energy supply to the bacteria in the two humic lakes.     

Abundance and biomass of heterotrophic microorganisms in Lake Tanganyika

1. This study focused on heterotrophic microorganisms in the two main basins (north and south) of Lake Tanganyika during dry and wet seasons in 2002. Bacteria (81% cocci) were abundant (2.28–5.30 × 10⁶ cells mL^?1). During the dry season, in the south basin, bacterial biomass reached a maximum of 2.27 g C m^?2 and phytoplankton biomass was 3.75 g C m^?2 (integrated over a water column of 100 m). 2. Protozoan abundance was constituted of 99% of heterotrophic nanoflagellates (HNF). Communities of flagellates and bacteria consisted of very small but numerous cells. Flagellates were often the main planktonic compartment, with a biomass of 3.42–4.43 g C m^?2. Flagellate biomass was in the same range and often higher than the total autotrophic biomass (1.60–4.72 g C m^?2). 3. Total autotrophic carbon was partly sustained by the endosymbiotic zoochlorellae Strombidium. These ciliates were present only in the euphotic zone and usually contributed most of the biomass of ciliates. 4. Total heterotrophic ciliate biomass ranged between 0.35 and 0.44 g C m^?2. In 2002, heterotrophic microorganisms consisting of bacteria, flagellates and ciliates represented a large fraction of plankton. These results support the hypothesis that the microbial food web contributes to the high productivity of Lake Tanganyika. 5. As the sole source of carbon in the pelagic zone of this large lake is phytoplankton production, planktonic heterotrophs ultimately depend on autochthonous organic carbon, most probably dissolved organic carbon (DOC) from algal excretion.     

Microbial community structure of sandy intertidal sediments in the North Sea, Sylt-Rømø Basin, Wadden Sea

Molecular biological methods were used to investigate the microbial diversity and community structure in intertidal sandy sediments near the island of Sylt (Wadden Sea) at a site which was characterized for transport and mineralization rates in a parallel study (D. de Beer, F. Wenzhöfer, T. Ferdelman, S.E. Boehme, M. Huettel, J.E.E. van Beusekom, M.E. Böttcher, N. Musat, N. Dubilier, Transport and mineralization rates in North Sea sandy intertidal sediments, Sylt-Romo Basin, Wadden Sea, Limnol. Oceanogr. 50 (2005) 113–127). Comparative 16S rRNA sequence analysis revealed a high bacterial diversity. Most sequences retrieved by PCR with a general bacterial primer set were affiliated with Bacteroidetes, Gammaproteobacteria, Deltaproteobacteria and the Pirellula cluster of Planctomycetales. Fluorescence in situ hybridization (FISH) and slot-blot hybridization with group-specific rRNA-targeted oligonucleotide probes were used to characterize the microbial community structure over depth (0–12 cm) and seasons (March, July, October). We found high abundances of bacteria with total cell numbers up to 3×10⁹ cells ml⁻¹ and a clear seasonal variation, with higher values in July and October versus March. The microbial community was dominated by members of the Planctomycetes, the Cytophaga/Flavobacterium group, Gammaproteobacteria, and bacteria of the Desulfosarcina/Desulfococcus group. The high abundance (1.5×10⁷–1.8×10⁸ cells ml⁻¹ accounting for 3–19% of all cells) of presumably aerobic heterotrophic polymer-degrading planctomycetes is in line with the high permeability, deep oxygen penetration, and the high rates of aerobic mineralization of algal biomass measured in the sandy sediments by de Beer et al. (2005). The high and stable abundance of members of the Desulfosarcina/Desulfococcus group, both over depth and season, suggests that these bacteria may play a more important role than previously assumed based on low sulfate reduction rates in parallel cores (de Beer et al., 2005).     

A 30% reduction in switchgrass rhizome reserves did not decrease biomass yield

A long-standing question in perennial grass breeding and physiology is whether yield improvement strategies could compromise winter survival. Since perennial grasses rely on stored carbohydrates for winter maintenance and spring regrowth, yield improvement strategies could reduce winter survival if they increase biomass and grain yields at the expense of carbon allocation to storage. Therefore, it is crucial to comprehend the dependence of regrowth on storage reserves. We experimentally depleted switchgrass (Panicum virgatum L.) rhizome reserves by storing rhizomes for 2 weeks at 5°C (control treatment) and 25°C (reserve-depleted treatment). During the storage period rhizome respiration was 5.3× higher at 25°C (0.010 μmol CO₂ g⁻¹ min⁻¹ at 5°C vs. 0.054 μmol CO₂ g⁻¹ min⁻¹ at 25°C; p < 0.0001) and the starch content was depleted by 30% by the end of storage. Surprisingly, reserve-depleted switchgrass had 60% larger leaf area (LA; LA_control = 149 cm² pot⁻¹ vs. LA_depleted = 239 cm² pot⁻¹; p = 0.013) and produced ~40% more aboveground biomass than control plants (9.46 g pot⁻¹ vs. 6.63 g pot⁻¹; p = 0.112). In addition, reserve-depleted switchgrass restored its rhizome starch reserves to pre-storage levels. Switchgrass showed a large plasticity among its source-sink components to buffer the imposed reserve depletion. It increased plant photosynthesis by increasing the photosynthetic leaf area while keeping photosynthesis constant on a leaf area basis and readjusted the timing and activity of sink organs. These results suggest that switchgrass, and potentially other perennial grasses, largely over-invest in storage reserves. Therefore, current breeding strategies in perennial grasses aimed to extend the aboveground growing season should not compromise crop persistence. Our study also has implications on long-term yield dynamics as it highlights sink limitations as potential driver of the yield decline commonly observed in perennial grasses 5+ years after cultivation.     

Microbial plankton across Drake Passage

We determined biomass and activity of microbial plankton across the Polar Front (PF) in Drake Passage during January 1994. Temperature was around 0°C south and between 3 and 5°C north of the PF. Both biomass and activities of microorganisms were significantly lower in the Antarctic waters south of the PF than in the sub-Antarctic waters north of it. Thus, values of chlorophyll a, integrated between 0 and 200 m, reached 150 mgm⁻² north, but only 25 mg m⁻² south of the PF. Likewise, bacteria varied between 10¹⁴ and 4×10¹³ cells m⁻². However, the abundance of heterotrophic nanoflagellates was extremely low throughout Drake Passage (around 3×10¹⁰ cells m⁻²). Bacterial doubling times were long (mean of 25 days). Bacterivory was estimated from the abundance of predators and prey and from temperature. The grazing impact on bacterioplankton biomass was insignificant (less that 0.05% per day) and low on bacterial heterotrophic production (15% per day). Neither biomass nor the activities of microorganisms were found to increase at the PF. The microbial food web was uncoupled and the bacteria did not seem to be controlled by predation.     

Trace amounts of nickel in belowground rhizomes of Vaccinium myrtillus L. decrease anthocyanin concentrations in aerial shoots without water stress

Nickel (Ni) may impair plant water balance through detrimental effects on the belowground level. Bilberry (Vaccinium myrtillus L.) plants were grown in a mesic heath forest-type soil and subjected to Ni sulphate (NiSO₄·6H₂O) concentrations of 0, 10, 50, 100 and 500 mg m⁻² during an entire growing season in northern Finland (65°N). Biomass of belowground rhizomes, and tissue water content (TWC) and anthocyanin concentrations of aerial shoots were determined from mature plants in order to study rhizospheric Ni stress, and its possible long-distance effects on aerial shoots. As the major proportion of biomass of bilberry is invested in belowground parts, it was hypothesised that Ni-induced rhizospheric disturbance causes water stress in aerial shoots and increases their anthocyanin concentrations for osmotic regulation. Uptake of Ni from the soil to the rhizome and aerial shoots was measured with X-ray fluorescence spectrometry. Ni concentrations in the soil and rhizome exhibited a dose–response relationship, but the concentrations in the rhizome were about 10-fold lower (<3 mg Ni kg⁻¹) than those in the soil (<30 mg Ni kg⁻¹). Translocation of Ni from the rhizome to aerial shoots did not occur, as Ni concentrations in shoots remained at 1 mg Ni kg⁻¹. Although Ni concentrations in the rhizome were below the threshold values of Ni toxicity (i.e. 10–50 mg Ni kg⁻¹), Ni decreased the rhizome biomass. Anthocyanins decreased in aerial shoots along with the Ni accumulation in the rhizome, while TWC was unaffected. The result suggests that anthocyanins are not involved in osmotic regulation under Ni stress, since anthocyanins in aerial shoots responded to the Ni concentrations in the rhizome despite the lack of water stress.     

Abundance and production of bacteria, and relationship to phytoplankton production, in a large tropical lake (Lake Tanganyika)

1. Abundance and bacterial production (BP) of heterotrophic bacteria (HBact) were measured in the north and south basins of Lake Tanganyika, East Africa, during seasonal sampling series between 2002 and 2007. The major objective of the study was to assess whether BP can supplement phytoplankton particulate primary production (particulate PP) in the pelagic waters, and whether BP and particulate PP are related in this large lake. HBact were enumerated in the 0–100 m surface layer by epifluorescence microscopy and flow cytometry; BP was quantified using ³H‐thymidine incorporation, usually in three mixolimnion layers (0–40, 40–60 and 60–100 m). 2. Flow cytometry allowed three subpopulations to be distinguished: low nucleic acid content bacteria (LNA), high nucleic acid content bacteria (HNA) and Synechococcus‐like picocyanobacteria (PCya). The proportion of HNA was on average 67% of total bacterial abundance, and tended to increase with depth. HBact abundance was between 1.2 × 10⁵ and 4.8 × 10⁶ cells mL⁻¹, and was maximal in the 0–40 m layer (i.e. roughly, the euphotic layer). Using a single conversion factor of 15 fg C cell⁻¹, estimated from biovolume measurements, average HBact biomass (integrated over a 100‐m water column depth) was 1.89 ± 1.05 g C m⁻². 3. Significant differences in BP appeared between seasons, especially in the south basin. The range of BP integrated over the 0–100 m layer was 93–735 mg C m⁻² day⁻¹, and overlapped with the range of particulate PP (150–1687 mg C m⁻² day⁻¹) measured in the same period of time at the same sites. 4. Depth‐integrated BP was significantly correlated to particulate PP and chlorophyll‐a, and BP in the euphotic layer was on average 25% of PP. 5. These results suggest that HBact contribute substantially to the particulate organic carbon available to consumers in Lake Tanganyika, and that BP may be sustained by phytoplankton‐derived organic carbon in the pelagic waters.     

The sulfate-reducing bacterial community of sulfide-rich water of the Ust’-Kachka resort spring, Perm Krai, Russia

Microbiological investigation of the highly mineralized, sulfide-rich cold spring of the Ust??-Kachka resort was carried out. The total number and biomass of microbial cells were 50 × 10³ cell/mL and 15 ??g/L, respectively. While the total microbial number was low, the sulfate reduction rate determined by the radioisotope method was relatively high (0.575 mg S L^?1 day^?1). An enrichment culture was obtained on Widdel medium. According to the results of cloning the 16S rRNA gene fragments with subsequent restriction analysis, the dominant organisms were group 6 sulfate-reducing bacteria (Desulfovibrio-Desulfomicrobium) and the microorganism exhibiting 99% similarity to the anaerobic haloalkaliphilic bacterium Halanaerobium hydrogeniformans.     

Reevaluation of the rate constants for the reaction of hypochlorous acid (HOCl) with cysteine,methionine, and peptide derivatives using a new competition kinetic approach

Activated white cells use oxidants generated by the heme enzyme myeloperoxidase to kill invading pathogens. This enzyme utilizes H₂O₂ and Cl⁻, Br⁻, or SCN⁻ to generate the oxidants HOCl, HOBr, and HOSCN, respectively. Whereas controlled production of these species is vital in maintaining good health, their uncontrolled or inappropriate formation (as occurs at sites of inflammation) can cause host tissue damage that has been associated with multiple inflammatory pathologies including cardiovascular diseases and cancer. Previous studies have reported that sulfur-containing species are major targets for HOCl but as the reactions are fast the only physiologically relevant kinetic data available have been extrapolated from data measured at high pH (>10). In this study these values have been determined at pH 7.4 using a newly developed competition kinetic approach that employs a fluorescently tagged methionine derivative as the competitive substrate (k(HOCl + Fmoc-Met), 1.5×10⁸ M⁻¹ s⁻¹). This assay was validated using the known k(HOCl + NADH) value and has allowed revised k values for the reactions of HOCl with Cys, N-acetylcysteine, and glutathione to be determined as 3.6×10⁸, 2.9×10⁷, and 1.24×10⁸ M⁻¹ s⁻¹, respectively. Similar experiments with methionine derivatives yielded k values of 3.4×10⁷ M⁻¹ s⁻¹ for Met and 1.7×10⁸ M⁻¹ s⁻¹ for N-acetylmethionine. The k values determined here for the reaction of HOCl with thiols are up to 10-fold higher than those previously determined and further emphasize the critical importance of reactions of HOCl with thiol targets in biological systems.     

Effect of detritus supply on trophic relationships within experimental benthic food webs. II. Microbial responses,fate and composition of decomposing detritus

The dynamics of bacterial, protozoan and fungal populations were examined in a long-term (40–55 wk) microcosm experiment designed to assess the effects of detritus supply on meiofauna-polychaete (Capitella capitata (Type I) Fabricius) interactions. Bacterial and protozoan numbers and bacterial growth rates were inversely correlated with population fluctuations of the polychaete at low (50 mg N · m^?2 · day ^?1) detritus supply, but did not correlate with fluctuating polychaete densities at two higher (100 and 150 mg N · m^?2 · day^?1) ration levels of detritus. Bacterial and protozoan numbers and bacterial growth rates did not correlate with standing amounts of detritus or with fungi or meiofauna at any of the detritus rations. Fungi were associated primarily with aggregates of detritus particles and fecal pellets produced by C. capitata.Labile (fiber-free) organic matter did not correlate with microbes or meiofauna, but was inversely correlated with population fluctuations of the polychaete C. capitata at all three ration levels of detritus. Polychaete fecal pellets accounted for most of the refractory matter in the tanks with C. capitata and did not accumulate in the sediments, suggesting that fecal pellets were continually being produced, broken apart and decomposed.Our experiments suggest that contradictions in previous studies on the effects of macroconsumers on microbes, especially bacteria, can be explained as a failure to consider the effects of detritus supply on microbial growth rates.