Bacterial diversity in relation to secondary production and succession on surfaces of the kelp Laminaria hyperborea

Kelp forests worldwide are known as hotspots for macroscopic biodiversity and primary production, yet very little is known about the biodiversity and roles of microorganisms in these ecosystems. Secondary production by heterotrophic bacteria associated to kelp is important in the food web as a link between kelp primary production and kelp forest consumers. The aim of this study was to investigate the relationship between bacterial diversity and two important processes in this ecosystem; bacterial secondary production and primary succession on kelp surfaces. To address this, kelp, Laminaria hyperborea, from southwestern Norway was sampled at different geographical locations and during an annual cycle. Pyrosequencing (454-sequencing) of amplicons of the 16S rRNA gene of bacteria was used to study bacterial diversity. Incorporation of tritiated thymidine was used as a measure of bacterial production. Our data show that bacterial diversity (richness and evenness) increases with the age of the kelp surface, which corresponds to the primary succession of its bacterial communities. Higher evenness of bacterial operational taxonomical units (OTUs) is linked to higher bacterial production. Owing to the dominance of a few abundant OTUs, kelp surface biofilm communities may be characterized as low-diversity habitats. This is the first detailed study of kelp-associated bacterial communities using high-throughput sequencing and it extends current knowledge on microbial community assembly and dynamics on living surfaces.     

Annual Bacterioplankton Biomasses and Productivities in a Temperate West Coast Canadian Fjord

Bacterioplankton numbers, biomasses, and productivities, as well as chlorophyll a concentrations and phytoplankton productivities, were assayed from 1 March 1984 to 12 August 1985 through a 250-m-deep seawater column in Howe Sound, a temperate fjord-sound on the southern coast of British Columbia, Canada. Primary production during this 18-month period was 845 g of C m⁻². Bacterial production was assayed over this same period as 193 g of C m⁻² (thymidine incorporation) and 77 g of C m⁻² (frequency of dividing cells). Bacterial productivities per cubic meter were usually greater in the euphotic zone than in deeper aphotic water, but when integrated through the water column, approximately half of the bacterial production occurred in the deeper aphotic portion. Bacterial production occurred throughout the year, although at reduced rates in late fall and early winter; primary production almost ceased during late fall and early winter. Because of this heterotrophic bacterioplankton production was a very large portion of the microbial (bacterial plus phyto-plankton) production at this time. In mid-summer bacterial production was a small proportion of the microbial production. Because of this asynchrony in peaks and troughs of bacterial and phytoplankton production through the year, data comparison is best done over an annual cycle. On this basis the bacterial production in the Howe Sound water column was between 23 and 9% of the phytoplankton production when a bacterial C to biovolume ratio of 0.107 pg of C μm⁻³ was assumed; the corresponding values were 64 and 29% when a ratio of 0.300 pg of bacterial C μm⁻³ was assumed.     

Primary and Bacterial Production in Two Dimictic Indiana Lakes

The relationship between primary and bacterial production in two dimictic Indiana lakes with different primary productivities was examined during the summer stratification period in 1982. Primary production rates were calculated from rates of H¹⁴CO₃⁻ incorporation by natural samples, and bacterial production was calculated from rates of [³H-methyl]thymidine incorporation by natural samples. Both vertical and seasonal distributions of bacterial production in the more productive lake (Little Crooked Lake) were strongly influenced by primary production. A lag of about 2 weeks between a burst in primary production and the subsequent response in bacterial production was observed. The vertical distribution of bacterial production in the water column of the less productive lake (Crooked Lake) was determined by the vertical distribution of primary production, but no clear relationship between seasonal maxima of primary and bacterial production in this lake was observed. High rates of bacterial production in Crooked Lake during May indicate the importance of allochthonous carbon washed in by spring rains. Bacterial production accounted for 30.6 and 31.8% of total (primary plus bacterial) production in Crooked Lake and Little Crooked Lake, respectively, from April through October. High rates of bacterial production during late September and October were observed in both lakes. Calculation of the fraction of bacterial production supported by phytoplankton excretion implies an important role for other mechanisms of supplying carbon, such as phytoplankton autolysis. Several factors affecting the calculation of bacterial production from the thymidine incorporation rates in these lakes were examined.     

Bacteria and heterotrophic microflagellate production in the Santa Rosa Sound, Florida

Bacterial and microflagellate biomass and production and grazing onbacteria were compared weekly at a fixed station in Santa Rosa Sound,Florida, starting in February and ending in October. For bothpopulations the weekly variation in biomass and production was aslarge as the seasonal variation. Cycles for biomass and production ofthese organisms were generally out of phase, rendering it difficultto estimate the net grazing of bacteria by microflagellates atindividual time points. For evaluation of factors that control thefate of carbon cycled by bacterial, experiments were conducted toexamine bacterial growth rates in the absence of predators. Thisexamination resulted in low bacterial growth rates when biomass washigh, and rapid growth rates typically occurred near minimumpopulations. Further analysis suggested that microflagellatepredation was greater than bacterial production during minimumbacterial growth rates. With integration of production and grazingrates over the study period, factors controlling bacterial growthwere examined. Using this approach, 71% of the bacterial productionwas grazed by < 8.0µm predators. The microflagellate biomassproduction was 41% of the grazing rate on bacteria. The total amountof bacterial production assimilated into microflagellate biomass was29%. However, based on the variations in biomass and activity of themicrobial assemblages, it appears that substrate and predation exertalternating control on bacterial abundance and production.     

Nutritional enrichment of a microbial community: The effects on activity, elemental composition, community structure and virus production

Abstract Viruses are active members of the microbial community in natural waters but little is known about the factors that regulate their activity and production. In this study we have investigated the effects of increased availability of organic nutrients and inorganic phosphate on activity, elemental composition, community structure and virus production in a natural bacterial community. The fraction of active cells in the community as estimated from microautoradiography of cells assimilating ³H-labeled thymidine ranged from 0–22%, but changes in the elemental composition of the cells indicated that more than 90% of the cells were active. The increase in carbon and energy availability stimulated virus production more than bacterial biomass production, while the increase in phosphate availability stimulated biomass production rather than virus production. A decrease in morphological diversity of the bacterial community was paralleled by a reduction in the virus-to-bacteria ratio (VBR) but the relationship between bacterial diversity and viral activity is uncertain. Our general conclusion is that nutrient availability, in addition to the bacterial activity, also affects the viral activity, and that both of these may affect the structure and diversity of the bacterial community.     

Modelling the importance of sediment bacterial carbon for profundal macroinvertebrates along a lake nutrient gradient

In dimictic, temperate lakes little is known about the quantitative importance of trophic coupling between pelagic and profundal communities. Although it is a generally accepted paradigm that profundal secondary production is dependent on autochthonous pelagic production (primarily diatoms), the importance of interactions between phytodetrital inputs, sediment bacteria, and macroinvertebrates are still not well understood. In this study, we used theoretical models to estimate macroinvertebrate carbon requirement (production + respiration) and bacterial production for lakes of different trophic categories. Comparisons of estimates show that the importance of bacterial production as a carbon source for benthic macroinvertebrates is inversely related to lake trophic state. Assuming that infauna assimilates 50% of ingested bacterial carbon, this food source could account for between 47% (oligotrophic lakes) and 2% (hypertrophic lakes) of their carbon demand. These calculations indicate that bacterial carbon should not be an important C-resource for profundal macroinvertebrates of eutrophic and hypertrophic lakes.     

Bacterial Production in the Recently Flooded Sep Reservoir: Diel Changes in Relation to Dissolved Carbohydrates and Combined Amino Acids

The spatial distribution of bacterial abundance and production were measured every 4 h in a recently flooded oligo-mesotrophic reservoir (the Sep Reservoir, Puy-De-Dôme, France), in relation to concentrations of dissolved carbohydrates and combined amino acids. The concentration of dissolved organic matter (DOM) components in the recently flooded Sep Reservoir were higher than those measured in other lakes of similar trophic status. Short-term variations in the bacterial production in this new reservoir appeared cyclical and endogenous to bacterial communities. These results highlight the need for the evaluation of diel changes in bacterial production, if estimation of the daily production rate of bacteria is to be done accurately for a reliable model of carbon flow through bacterioplankton and ultimately through aquatic microbial food webs. Bacterial growth, measured over time and space, did not appear exclusively governed by DOM components from phytoplankton primary production.     

Lactose-Enhanced Cellulase Production by Microbacterium sp. Isolated from Fecal Matter of Zebra (Equus zebra)

A cellulase-producing bacterial strain designated Z5 was isolated from the fecal matter of Zebra (Equus zebra). The strain was identified as Microbacterium sp. on the basis of 16S rDNA sequence analysis. The effect of substrates like CMC, avicel, starch, maltose, sucrose, glucose, fructose, galactose, and lactose on cellulase production was also determined. Lactose as the sole carbon source induced cellulase production in this bacterial strain and a positive synergistic effect of lactose and CMC was also observed with enhancement of 3-4 times in cellulase activity. The optimum cellulase production was recorded with 3% CMC and 1% lactose when added individually in the Omeliansky's medium. The optimum temperature and time for cellulase production by this bacterial strain was 37°C and 10 days, respectively. To our knowledge this is the first report on enhancement of cellulase production by lactose in the Microbacterium sp.     

Bacterioplankton and phytoplankton production in a large patagonian reservoir (República Argentina)

Relationships between the secondary production of bacterioplankton and the primary production of phytoplankton in the Ezequiel Ramos Mexia Reservoir were examined. Monthly surveys, parallel measurements on consecutive days, and measurements at different times during the same day were undertaken to determine factors that might influence the relationships between the two sets of productivity measurements.The vertical and seasonal distribution of bacterial production appeared to be strongly related to primary production, with temperature as an important component of this trend. The bacterial production in the water column was equivalent to between 2 and 45% of the phytoplankton production over a period of one year.In a diel study, bacterial secondary production rates fluctuated, with maximum values during the night and early morning. There was no temporal coincidence between algal primary production and bacterial secondary production in daily surveys. It was therefore concluded that isolated measurements of productivity reflect events only at the particular time at which they are obtained. The relationship between algae and bacteria is extremely complex and must be carefully evaluated. The nature of the relationship could be underevaluated if the only measurements taken into consideration were made during the daylight period.     

Relationship between bacterial and primary production in a newly filled reservoir: temporal variability over 2 consecutive years

Seasonal and spatial variations in bacterial abundance, biomass and production in a recently flooded reservoir were followed for 2 consecutive years, in conjunction with phytoplankton biomass (chlorophyll a) and activity (primary production). Between the 2 years of the study, the mean value of primary production remained constant, while those of the chlorophyll a concentration, bacterial abundance (BA), bacterial biomass (BB) and bacterial production (BP) decreased. The observed trends of the bacterial variables were linked to changes in the relative importance of allochthonous dissolved organic matter. Moreover, this factor would explain discrepancies observed between the slope of the model II regression equations established from results of the present study and those of the predictive models from the literature, relating to bacterial and phytoplankton variables. An estimate of the carbon budget indicated that 22 and 5% of the ambient primary production in the Sep Reservoir might be channeled through the microbial loop via BP during the 1st and 2nd year of the study, respectively. We conclude that heterotrophic BP in the Sep Reservoir may, on occasion, represent a significant source of carbon for higher order consumers.     

The impact of zooplankton feeding on the epilimnetic bacteria of a eutrophic lake

SUMMARY. The members of the zooplankion eat bacteria in natural systems, but the impact of this mechanism of removal of bacterial biomass on the bacterioplankton of freshwaters is unknown. Zooplankton abundance and biomass were followed for 2 years in Lake Mendota. Bacterial biomass and heterotrophic production were also assessed. Feeding of zooplankton on bacteria was measured by a cell counts method in 1979 and using radioactively labelled natural assemblages of bacteria in 1980. Total feeding was calculated and was found to account for l-60% of the bacterial biomass daily. Annually, it accounted for 1–10% of the bacterial heterotrophic production. Since bacterial biomass does not change significantly from year to year and yet bacterial production is very high compared to feeding by zooplankton, mechanisms other than feeding must exist which remove biomass from the epilimnetic bacteria in larger amounts.     

Synergy of Fresh and Accumulated Organic Matter to Bacterial Growth

The main goal of this research was to evaluate whether the mixture of fresh labile dissolved organic matter (DOM) and accumulated refractory DOM influences bacterial production, respiration, and growth efficiency (BGE) in aquatic ecosystems. Bacterial batch cultures were set up using DOM leached from aquatic macrophytes as the fresh DOM pool and DOM accumulated from a tropical humic lagoon. Two sets of experiments were performed and bacterial growth was followed in cultures composed of each carbon substrate (first experiment) and by carbon substrates combined (second experiment), with and without the addition of nitrogen and phosphorus. In both experiments, bacterial production, respiration, and BGE were always higher in cultures with N and P additions, indicating a consistent inorganic nutrient limitation. Bacterial production, respiration, and BGE were higher in cultures set up with leachate DOM than in cultures set up with humic DOM, indicating that the quality of the organic matter pool influenced the bacterial growth. Bacterial production and respiration were higher in the mixture of substrates (second experiment) than expected by bacterial production and respiration in single substrate cultures (first experiment). We suggest that the differences in the concentration of some compounds between DOM sources, the co-metabolism on carbon compound decomposition, and the higher diversity of molecules possibly support a greater bacterial diversity which might explain the higher bacterial growth observed. Finally, our results indicate that the mixture of fresh labile and accumulated refractory DOM that naturally occurs in aquatic ecosystems could accelerate the bacterial growth and bacterial DOM removal.     

The effect of temperature and algal biomass on bacterial production and specific growth rate in freshwater and marine habitats

We analyzed heterotrophic, pelagic bacterial production and specific growth rate data from 57 studies conducted in fresh, marine and estuarine/coastal waters. Strong positive relationships were identified between 1) bacterial production and bacterial abundance and 2) bacterial production and algal biomass. The relationship between bacterial production and bacterial abundance was improved by also considering water temperature. The analysis of covariance model revealed consistent differences between fresh, marine and estuarine/coastal waters, with production consistently high in estuarine/coastal environments. The log-linear regression coefficient of abundance was not significantly different from 1.00, and this linear relationship permitted the use of specific growth rate (SGR in day⁻¹) as a dependent variable. A strong relationship was identified between specific growth rate and temperature. This relationship differed slightly across the three habitats. A substantial portion of the residual variation from this relationship was accounted for by algal biomass, including the difference between marine and estuarine/coastal habitats. A small but significant difference between the fresh- and saltwater habitats remained. No significant difference between the chlorophyll effect in different habitats was identified. The model of SGR against temperature and chlorophyll was much weaker for freshwater than for marine environments. For a small subset of the data set, mean cell volume accounted for some of the residual variation in SGR. Pronounced seasonality, fluctuations in nutrient quality, and variation of the grazing environment may contribute to the unexplained variation in specific growth.     

Seasonal and vertical distribution of planktonic bacteria and heterotrophic nanoflagellates in the middle Adriatic Sea

Temporal and spatial patterns of bacteria and heterotrophic nanoflagellates (HNF) were studied monthly from January 1997 to December 1998 in the middle Adriatic Sea. Bacterial and HNF relationships with phytoplankton biomass and temperature were analyzed to examine how the relative importance of bottom-up and top-down factors may shift over seasons and locations. For the coastal area, an inconsistent relationship between bacterial abundance and chlorophyll a and a stronger relationship between bacterial abundance and bacterial production suggest that other substrates than those of phytoplankton origin are important for bacteria. The analysis of simultaneous effects of temperature and bacterial production on bacterial abundance showed that the effect of temperature obscured the effects of bacterial production, suggesting that bacterial growth itself is highly temperature-dependent. The relationship between HNF abundance and bacterial abundance was slightly improved by the inclusion of in situ temperature, bacterial production or both parameters, as additional independent variables. About 60% of the variability in HNF abundance can be explained by bacterial abundance, bacterial production and temperature. In the open sea, tight coupling of bacterial abundance with chlorophyll a concentrations implied that phytoplankton-derived substrates have a dominant role in controlling bacterial abundance. During the colder months, bacterial abundance was high enough to support higher HNF abundance than observed, suggesting that predation exerted a minor depressing influence on bacterial abundance during that period. During the spring-summer period, HNF controlled bacterial standing stocks by direct cropping of bacterial production.Communicated by: H.-D. Franke     

Reevaluation of Production of Paralytic Shellfish Toxin by Bacteria Associated with Dinoflagellates of the Portuguese Coast

Paralytic shellfish toxins (PSTs) are potent neurotoxins produced by certain dinoflagellate and cyanobacterial species. The autonomous production of PSTs by bacteria remains controversial. In this study, PST production by two bacterial strains, isolated previously from toxic dinoflagellates, was evaluated using biological and analytical methods. Analyses were performed under conditions determined previously to be optimal for toxin production and detection. Our data are inconsistent with autonomous bacterial PST production under these conditions, thereby challenging previous findings for the same strains.     

Regulation of Bacterial Growth Rates by Dissolved Organic Carbon and Temperature in the Equatorial Pacific Ocean

Abstract The effect of dissolved organic matter (DOM) and temperature on bacterial production was examined in the equatorial Pacific Ocean. Addition of glucose, glucose plus ammonium, or free amino acids stimulated bacterial production ([³H]thymidine incorporation), whereas changes in bacterial abundance were either negligible or much less than changes in bacterial production. The average bacterial growth rate also greatly increased following DOM additions, whereas in contrast, addition of ammonium alone never affected production, bacterial abundance, or growth rates. Since the large glucose effect was not observed in previous studies of cold oceanic waters, several experiments were conducted to examine DOM-temperature interactions. These experiments suggest that bacteria respond more quickly and to a greater extent to DOM additions at higher temperatures, which may explain apparently conflicting results from previous studies. We also examined how temperate affects the kinetic parameters of sugar uptake. Maximum uptake rates (V_max) of glucose and mannose increased with temperature (Q₁₀= 2.4), although the half-saturation constant (K_m) was unaffected; K_m+ S was roughly equal to glucose concentrations (S) measured by a high pressure liquid chromographic technique. Bacterial production and growth rates appear to be limited by DOM in the equatorial Pacific, and thus bacterial production follows primary production over large spatial and temporal scales in this oceanic regime, as has been observed in other aquatic systems. Although temperature may not limit bacterial growth rates in the equatorial Pacific and similar warm waters, it could still affect how bacteria respond to changes in DOM supply and help set steady-state DOM concentrations. Received: 26 July 1995; Revised: 19 January 1996     

Reevaluation of production of paralytic shellfish toxin by bacteria associated with dinoflagellates of the Portuguese coast

Paralytic shellfish toxins (PSTs) are potent neurotoxins produced by certain dinoflagellate and cyanobacterial species. The autonomous production of PSTs by bacteria remains controversial. In this study, PST production by two bacterial strains, isolated previously from toxic dinoflagellates, was evaluated using biological and analytical methods. Analyses were performed under conditions determined previously to be optimal for toxin production and detection. Our data are inconsistent with autonomous bacterial PST production under these conditions, thereby challenging previous findings for the same strains.     

Pelagic food web processes in an oligotrophic lake

Major pelagic carbon pathways, including primary production, release of extracellular products (EOC), bacterial production and zooplankton grazing were measured in oligotrophic Lake Almind (Denmark) and in enclosures (7 m³) subjected to artificial eutrophication. Simultaneous measurements at three days interval of carbon exchange rates and pools allowed the construction of carbon flow scenarios over a nineteen day experimental period.The flow of organic carbon was dominated by phytoplankton EOC release, which amounted from 44 to 58% of the net fixation of inorganic carbon. Gross bacterial production accounted for 33 to 75% of the primary production. The lower values of EOC release (44%) and bacterial production (33%) were found in the enclosures with added nutrients. The release of recently fixed photosynthetic products was the most important source of organic carbon to the bacterioplankton. Uptake of dissolved free amino acids was responsible for 52 to 62% of the gross bacterial production. Thus, amino acids constituted a significant proportion of the EOC. Zooplankton (< 50 µm) grazing on algae and bacteria accounted only for a minor proportion of the particulate production in May. Circumstantial evidence is presented that suggests the chrysophycean alga Dinobryon was the most important bacterial remover.The results clearly demonstrated EOC release and bacterial metabolism to be key processes in pelagic carbon cycling in this oligotrophic lake.     

Cheater suppression and stochastic clearance through quorum sensing

The evolutionary consequences of quorum sensing in regulating bacterial cooperation are not fully understood. In this study, we reveal unexpected effects of regulating public good production through quorum sensing on bacterial population dynamics, showing that quorum sensing can be a collectively harmful alternative to unregulated production. We analyze a birth-death model of bacterial population dynamics accounting for public good production and the presence of non-producing cheaters. Our model demonstrates that when demographic noise is a factor, the consequences of controlling public good production according to quorum sensing depend on the cost of public good production and the growth rate of populations in the absence of public goods. When public good production is inexpensive, quorum sensing is a destructive alternative to unconditional production, in terms of the mean population extinction time. When costs are higher, quorum sensing becomes a constructive strategy for the producing strain, both stabilizing cooperation and decreasing the risk of population extinction.     

Coupling Between Rates of Bacterial Production and the Abundance of Metabolically Active Bacteria in Lakes, Enumerated Using CTC Reduction and Flow Cytometry

Abstract In natural bacterioplankton assemblages, only a fraction of the total cell count is active, and, therefore, rates of bacterial production should be more strongly correlated to the number of active cells than to the total number of bacteria. However, this hypothesis has seldom been tested. Herein we explore the relationship between rates of bacterial production (measured as leucine uptake) and the number of active bacteria in 14 lakes in southern Québec. Active bacteria are defined as those cells capable of reducing the tetrazolium salt CTC to its fluorescent formazan; these cells were enumerated using flow cytometry. Bacterial production varied two orders of magnitude in the lakes studied, as did the number of active bacteria, whereas the total number of bacteria varied by only sixfold. The number and proportion of active bacteria were similar among lake strata, but rates of bacterial production were highest in the epilimnion and lowest in the hypolimnion. As expected, bacterial production was better correlated to the number of active cells, and bacterial growth rates calculated for active cells ranged from 0.7 to 1.8 day⁻¹, on average threefold higher than those calculated on the basis of total bacterial abundance. Growth rates scaled to active cells were, on average, similar among lake strata and did not show any pattern along a gradient of increasing chlorophyll concentration, so there was no systematic change of bacterial growth rates with lake productivity. In contrast, growth rates scaled to the entire bacterial assemblage were positively correlated to chlorophyll, were tenfold more variable among lakes than growth rates of active cells, and showed larger differences among lake strata. Scaling bacterial production to either the total number or the number of active cells thus results in very different patterns in bacterial growth rates among aquatic systems. Received: 12 July 1996; Accepted: 24 September 1996