Use of a fluorescent redox probe for direct visualization of actively respiring bacteria.

The redox dye 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) was employed for direct epifluorescent microscopic enumeration of respiring bacteria in environmental samples. Oxidized CTC is nearly colorless and is nonfluorescent; however, the compound is readily reduced via electron transport activity to fluorescent, insoluble CTC-formazan, which accumulates intracellularly. Bacteria containing CTC-formazan were visualized by epifluorescence microscopy in wet-mount preparations, on polycarbonate membrane filter surfaces, or in biofilms associated with optically opaque surfaces. Counterstaining of CTC-treated samples with the DNA-specific fluorochrome 4',6-diamidino-2-phenylindole allowed enumeration of active and total bacterial subpopulations within the same preparation. Municipal wastewater, groundwater, and seawater samples supplied with exogenous nutrients yielded CTC counts that were generally lower than total 4',6-diamidino-2-phenylindole counts but typically equal to or greater than standard heterotrophic (aerobic) plate counts. In unsupplemented water samples, CTC counts were typically lower than those obtained with the heterotrophic plate count method. Reduction of CTC by planktonic or biofilm-associated bacteria was suppressed by formaldehyde, presumably because of inhibition of electron transport activity and other metabolic processes. Because of their bright red fluorescence (emission maximum, 602 nm), actively respiring bacteria were readily distinguishable from abiotic particles and other background substances, which typically fluoresced at shorter wavelengths. The use of CTC greatly facilitated microscopic detection and enumeration of metabolically active (i.e., respiring) bacteria in environmental samples.     

Use of a fluorescent redox probe for direct visualization of actively respiring bacteria.

The redox dye 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) was employed for direct epifluorescent microscopic enumeration of respiring bacteria in environmental samples. Oxidized CTC is nearly colorless and is nonfluorescent; however, the compound is readily reduced via electron transport activity to fluorescent, insoluble CTC-formazan, which accumulates intracellularly. Bacteria containing CTC-formazan were visualized by epifluorescence microscopy in wet-mount preparations, on polycarbonate membrane filter surfaces, or in biofilms associated with optically opaque surfaces. Counterstaining of CTC-treated samples with the DNA-specific fluorochrome 4',6-diamidino-2-phenylindole allowed enumeration of active and total bacterial subpopulations within the same preparation. Municipal wastewater, groundwater, and seawater samples supplied with exogenous nutrients yielded CTC counts that were generally lower than total 4',6-diamidino-2-phenylindole counts but typically equal to or greater than standard heterotrophic (aerobic) plate counts. In unsupplemented water samples, CTC counts were typically lower than those obtained with the heterotrophic plate count method. Reduction of CTC by planktonic or biofilm-associated bacteria was suppressed by formaldehyde, presumably because of inhibition of electron transport activity and other metabolic processes. Because of their bright red fluorescence (emission maximum, 602 nm), actively respiring bacteria were readily distinguishable from abiotic particles and other background substances, which typically fluoresced at shorter wavelengths. The use of CTC greatly facilitated microscopic detection and enumeration of metabolically active (i.e., respiring) bacteria in environmental samples.     

A new medium for the enumeration and subculture of bacteria from potable water.

Plate count agar is presently the recommended medium for the standard bacterial plate count (35 degrees C, 48-h incubation) of water and wastewater. However, plate count agar does not permit the growth of many bacteria that may be present in treated potable water supplies. A new medium was developed for use in heterotrophic plate count analyses and for subculture of bacteria isolated from potable water samples. The new medium, designated R2A, contains 0.5 g of yeast extract, 0.5 g of Difco Proteose Peptone no. 3 (Difco Laboratories), 0.5 g of Casamino Acids (Difco), 0.5 g of glucose, 0.5 g of soluble starch, 0.3 g of K2HPO4, 0.05 g of MgSO4 X 7H2O, 0.3 g of sodium pyruvate, and 15 g of agar per liter of laboratory quality water. Adjust the pH to 7.2 with crystalline K2HPO4 or KH2PO4 and sterilize at 121 degrees C for 15 min. Results from parallel studies with spread, membrane filter, and pour plate procedures showed that R2A medium yielded significantly higher bacterial counts than did plate count agar. Studies of the effect of incubation temperature showed that the magnitude of the count was inversely proportional to the incubation temperature. Longer incubation time, up to 14 days, yielded higher counts and increased detection of pigmented bacteria. Maximal bacterial counts were obtained after incubation at 20 degrees C for 14 days. As a tool to monitor heterotrophic bacterial populations in water treatment processes and in treated distribution water, R2A spread or membrane filter plates incubated at 28 degrees C for 5 to 7 days is recommended.(ABSTRACT TRUNCATED AT 250 WORDS)     

A new medium for the enumeration and subculture of bacteria from potable water

Plate count agar is presently the recommended medium for the standard bacterial plate count (35 degrees C, 48-h incubation) of water and wastewater. However, plate count agar does not permit the growth of many bacteria that may be present in treated potable water supplies. A new medium was developed for use in heterotrophic plate count analyses and for subculture of bacteria isolated from potable water samples. The new medium, designated R2A, contains 0.5 g of yeast extract, 0.5 g of Difco Proteose Peptone no. 3 (Difco Laboratories), 0.5 g of Casamino Acids (Difco), 0.5 g of glucose, 0.5 g of soluble starch, 0.3 g of K2HPO4, 0.05 g of MgSO4 X 7H2O, 0.3 g of sodium pyruvate, and 15 g of agar per liter of laboratory quality water. Adjust the pH to 7.2 with crystalline K2HPO4 or KH2PO4 and sterilize at 121 degrees C for 15 min. Results from parallel studies with spread, membrane filter, and pour plate procedures showed that R2A medium yielded significantly higher bacterial counts than did plate count agar. Studies of the effect of incubation temperature showed that the magnitude of the count was inversely proportional to the incubation temperature. Longer incubation time, up to 14 days, yielded higher counts and increased detection of pigmented bacteria. Maximal bacterial counts were obtained after incubation at 20 degrees C for 14 days. As a tool to monitor heterotrophic bacterial populations in water treatment processes and in treated distribution water, R2A spread or membrane filter plates incubated at 28 degrees C for 5 to 7 days is recommended.(ABSTRACT TRUNCATED AT 250 WORDS)     

A method of the selective isolation and enumeration of marine Vibrionaceae

A noninhibitory medium and GasPack anaerobic culture system were employed for the selective enumeration and isolation of Vibrionaceae in seawater and marine sediments.Vibrio counts obtained by the new method for seawater and sediment samples were compared with vibrio numbers in the heterotrophic bacterial population appearing on a medium routinely employed in the laboratory for such counts. The ratio of the former to the latter counts ranged from 0.5 to 1.3, the average being 0.96. The seawater and sediment bacteria that grew and produced visible colonies on the medium under anaerobic conditions for 3 days at 20°C were almost exclusively vibrios.From the results reported here it is concluded that most of the vibrios present in seawater and sediment samples can be recovered by the new method developed in this study.     

Distribution and Physiology of Aerobic Bacteria Containing Bacteriochlorophyll a on the East and West Coasts of Australia

Aerobic heterotrophic bacteria containing bacteriochlorophyll were isolated from specimens from a wide variety of marine environments on the west (Shark Bay, Lake Clifton, Lake Heyward, and Perth) and east (near Townsville and Brisbane) coasts of Australia. The bacteria were found in a high proportion (10 to 30%) of the total heterotrophic bacterial strains isolated from marine algae, seagrasses, stromatolites, the epiphytes on stromatolites, seawater, and sands; in some cases they constituted up to 49% of the total. This is much higher than the previous report of 6% from Japan. A high percentage, 13%, was also found in the seawater of Hamelin Pool, at Shark Bay, where the salinity was 66%. The number of these bacteria was generally low in seawater and sands, with a few exceptions. There were no aerobic bacteriochlorophyll-containing bacteria on sponges or corals. The isolated strains were orange or pink, and most had absorption maxima around 800 and 850 to 870 nm, the latter range being the absorption of bacteriochlorophyll a in vivo. The maximum bacteriochlorophyll content was 1 nmol/mg (dry weight) of bacterial cells. Most of the bacteria did not grow phototrophically under anaerobic conditions in a broth medium containing succinate. Cells and cell extracts grown under aerobic conditions had photochemical activities such as reversible photooxidations of the reaction center and cytochrome(s). Some strains showed denitrifying activity. The optimal salinity for bacterial growth varied between strains.     

Oligotrophic bacterioplankton with a novel single-cell life strategy

A large fraction of the marine bacterioplankton community is unable to form colonies on agar surfaces, which so far no experimental evidence can explain. Here we describe a previously undescribed growth behavior of three non-colony-forming oligotrophic bacterioplankton, including a SAR11 cluster representative, the world's most abundant organism. We found that these bacteria exhibit a behavior that promotes growth and dispersal instead of colony formation. Although these bacteria do not form colonies on agar, it was possible to monitor growth on the surface of seawater agar slides containing a fluorescent stain, 4',6'-diamidino-2-phenylindole (DAPI). Agar slides were prepared by pouring a solution containing 0.7% agar and 0.5 micro g of DAPI per ml in seawater onto glass slides. Prompt dispersal of newly divided cells explained the inability to form colonies since immobilized cells (cells immersed in agar) formed microcolonies. The behavior observed suggests a life strategy intended to optimize access of individual cells to substrates. Thus, the inability to form colonies or biofilms appears to be part of a K-selected population strategy in which oligotrophic bacteria explore dissolved organic matter in seawater as single cells.     

The uptake of inorganic nutrients by heterotrophic bacteria

It is now well known that heterotrophic bacteria account for a large portion of total uptake of both phosphate (60% median) and ammonium (30% median) in freshwaters and marine environments. Less clear are the factors controlling relative uptake by bacteria, and the consequences of this uptake on the plankton community and biogeochemical processes, e.g., new production. Some of the variation in reported inorganic nutrient uptake by bacteria is undoubtedly due to methodological problems, but even so, uptake would be expected to vary because of variation in several parameters, perhaps the most interesting being dissolved organic matter. Uptake of ammonium by bacteria is very low whereas uptake of dissolved free amino acids (DFAA) is high in eutrophic estuaries (the Delaware Bay and Chesapeake Bay). The concentrations and turnover of DFAA are insufficient, however, in oligotrophic oceans where bacteria turn to ammonium and nitrate, although the latter only as a last resort. I argue here that high uptake of dissolved organic carbon, which has been questioned, is necessary to balance the measured uptake of dissolved inorganic nitrogen (DIN) in seawater culture experiments. What is problematic is that this DIN uptake exceeds bacterial biomass production. One possibility is that bacteria excrete dissolved organic nitrogen (DON). A recent study offers some support for this hypothesis. Lysis by viruses would also release DON.While ammonium uptake by heterotrophic bacteria has been hypothesized to affect phytoplankton community structure, other impacts on the phytoplankton and biomass production (both total and new) are less clear and need further work. Also, even though bacteria account for a very large fraction of phosphate uptake, how this helps to structure the plankton community has not been examined. What is clear is that the interactions between bacterial and phytoplankton uptake of inorganic nutrients are more complicated than simple competition.     

不同寡营养培养条件下南海水体细菌群落结构及其对碳源的利用特征

【背景】绝大多数海洋微生物不可培养,为挖掘海洋生态系统中可培养的微生物资源,研究者尝试寡营养培养等方法。【目的】比较不同寡营养培养条件下南海水体细菌数量、群落结构及其对碳源的利用特征差异。【方法】采用原2216E培养液(Y)、稀释10倍(Y-10)和稀释50倍(Y-50)的2216E培养液培养南海海水样品,用荧光定量PCR法和16S rRNA基因检测细菌数量和菌群结构;利用平板计数法计数异养细菌的数量,纯化鉴定可培养细菌;采用Biolog EcoPlateTM微板法分析不同培养基中细菌群落对碳源的利用特征。【结果】Y组细菌总数高于Y-10组和Y-50组,差异不显著(P>0.05),但异养细菌数量显著高于Y-10组和Y-50组(P<0.05)。16S rRNA基因测序结果表明,不同稀释倍数下的细菌群落结构差异明显,Y组检测出10门193属,优势类群为Proteobacteria(56.44%)和Bacteroides (37.27%);Y-10组检测出15门220属,优势类群为Proteobacteria (40.30%)、Bacteroides(36.91%)和Firmic...     

Bacterial uptake of algal extracellular products: an experimental approach

Methods for partitioning planktonic algal and bacterial populations were examined. If samples were filtered under gravity through a 1 μm pore size Nuclepore polycarbonate membrane the algae were retained on the filter and most (usually > 80%) of the bacteria were found in the filtrate. The application of any vacuum or pressure during this process resulted in the appearance of chlorophyll in the filtrate. In radiotracer experiments this would lead to an overestimate of ¹⁴C incorporation into the bacteria. There was excellent agreement between measurements of partition efficiency by epifluorescence direct counts of bacteria and by uptake of trace quantities of tritiated glucose. The methods were applied to the measurement of algal excretion of dissolved organic matter and its uptake by bacteria over light-dark cycles. An illuminated water bath was adapted to provide shortened (3–24 h) light-dark cycles which could be used to examine interactions between individual algal and bacterial species. Estimates of bacterial heterotrophic production based on the assimilation of labelled algal extracellular products were lower than those calculated from the incorporation of SO^2-₄.     

Growth characteristics of low-nutrient bacteria from the north-east and central Pacific Ocean

Abstract Low-nutrient, or oligotrophic, marine bacteria, defined operationally as those which grow well in the dilute nutrient concentrations typical of natural seawaters, were found in waters of the eastern and central Pacific Ocean. All isolates tested grew in sterile unsuplemented seawater, ultraviolet-irradiated seawater, artificial seawater and charcoal-treated artificial seawater. Under optimal conditions, doubling times for low-nutrient bacteria were generally 2–5 h. Low-nutrient bacteria are heterotrophs responding to added organic substrates including glucose, proline, acetate, peptone, algal extract and yeast extract. Organic substrate concentrations ( K _s values) necessary to yield half the maximum growth rates of low-nutrient bacteria ranged from 0.8–12 μg · 1⁻¹ (0.2–4.9 μg C · 1⁻¹). Bacterial inoculum size had little effect on doubling times, whereas low oxygen tensions and low temperatures reduced growth rates. Surfaces (glass beads) increased growth rates and maximum cell densities. The results of these laboratory studies indicate that low-nutrient bacteria play a major role in marine heterotrophic transformations of dissolved organic matter.     

Oligotrophic Bacterioplankton with a Novel Single-Cell Life Strategy

A large fraction of the marine bacterioplankton community is unable to form colonies on agar surfaces, which so far no experimental evidence can explain. Here we describe a previously undescribed growth behavior of three non-colony-forming oligotrophic bacterioplankton, including a SAR11 cluster representative, the world's most abundant organism. We found that these bacteria exhibit a behavior that promotes growth and dispersal instead of colony formation. Although these bacteria do not form colonies on agar, it was possible to monitor growth on the surface of seawater agar slides containing a fluorescent stain, 4′,6′-diamidino-2-phenylindole (DAPI). Agar slides were prepared by pouring a solution containing 0.7% agar and 0.5 μg of DAPI per ml in seawater onto glass slides. Prompt dispersal of newly divided cells explained the inability to form colonies since immobilized cells (cells immersed in agar) formed microcolonies. The behavior observed suggests a life strategy intended to optimize access of individual cells to substrates. Thus, the inability to form colonies or biofilms appears to be part of a K-selected population strategy in which oligotrophic bacteria explore dissolved organic matter in seawater as single cells.     

Substrate Use of Pseudovibrio sp. Growing in Ultra-Oligotrophic Seawater

Marine planktonic bacteria often live in habitats with extremely low concentrations of dissolved organic matter (DOM). To study the use of trace amounts of DOM by the facultatively oligotrophic Pseudovibrio sp. FO-BEG1, we investigated the composition of artificial and natural seawater before and after growth. We determined the concentrations of dissolved organic carbon (DOC), total dissolved nitrogen (TDN), free and hydrolysable amino acids, and the molecular composition of DOM by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR-MS). The DOC concentration of the artificial seawater we used for cultivation was 4.4 μmol C L^-1, which was eight times lower compared to the natural oligotrophic seawater we used for parallel experiments (36 μmol C L ^-1). During the three-week duration of the experiment, cell numbers increased from 40 cells mL^-1 to 2x10⁴ cells mL ^-1 in artificial and to 3x10⁵ cells mL ^-1 in natural seawater. No nitrogen fixation and minor CO₂ fixation (< 1% of cellular carbon) was observed. Our data show that in both media, amino acids were not the main substrate for growth. Instead, FT-ICR-MS analysis revealed usage of a variety of different dissolved organic molecules, belonging to a wide range of chemical compound groups, also containing nitrogen. The present study shows that marine heterotrophic bacteria are able to proliferate with even lower DOC concentrations than available in natural ultra-oligotrophic seawater, using unexpected organic compounds to fuel their energy, carbon and nitrogen requirements.     

The use of R2A medium and the spread plate method for the enumeration of heterotrophic bacteria in drinking water

The pour plate method with yeast extract agar and a 3 d incubation period is the standard method in the UK for the enumeration of heterotrophic bacteria in drinking water. We have compared the standard method with other procedures using the spread plate technique, R2A medium and a longer incubation period. The R2A spread plate method with a 7 d incubation period gave an average estimate of bacterial numbers 520 times greater than for the standard method. This alternative method is recommended for obtaining a more accurate estimate of heterotrophic bacterial populations in drinking water.     

Dissolved extracellular polymeric substances (dEPS) dynamics and bacterial growth during sea ice formation in an ice tank study

Extracellular polymeric substances (EPS) are known to help microorganisms to survive under extreme conditions in sea ice. High concentrations of EPS are reported in sea ice from both poles; however, production and dynamics of EPS during sea ice formation have been little studied to date. This investigation followed the production and partitioning of existing and newly formed dissolved organic matter (DOM) including dissolved carbohydrates (dCHO), dissolved uronic acids (dUA) and dissolved EPS (dEPS), along with bacterial abundances during early stages of ice formation. Sea ice was formed from North Sea water with (A) ambient DOM (NSW) and (B) with additional algal-derived DOM (ADOM) in a 6d experiment in replicated mesocosms. In ADOM seawater, total bacterial numbers (TBN) increased throughout the experiment, whereas bacterial growth occurred for 5d only in the NSW seawater. TBN progressively decreased within developing sea ice but with a 2-fold greater decline in NSW compared to ADOM ice. There were significant increases in the concentrations of dCHO in ice. Percentage contribution of dEPS was highest (63%) in the colder, uppermost parts in ADOM ice suggesting the development of a cold-adapted community, producing dEPS possibly for cryo-protection and/or protection from high salinity brines. We conclude that in the early stages of ice formation, allochthonous organic matter was incorporated from parent seawater into sea ice and that once ice formation had established, there were significant changes in the concentrations and composition of dissolved organic carbon pool, resulting mainly from the production of autochthonous DOM by the bacteria.     

Bacterial colonization of domestic reverse-osmosis water filtration units

We have analyzed the bacterial content of water from the reservoirs of 300 reverse-osmosis units installed in households. The heterotrophic plate counts on R2A medium (20 and 35 degrees C) ranged from 0 to 10(7) colony forming units per millilitre (cfu/mL). Most reservoirs contained water with bacterial counts between 10(4) and 10(5) cfu/mL. The bacteria identified were Pseudomonas (not aeruginosa), Alcaligenes or Moraxella, Acinetobacter, Flavobacterium, and Chromobacterium. This report emphasizes the importance of bacterial colonization by heterotrophic bacteria in water reservoirs from domestic reverse-osmosis units.     

Bacterial Activity in a Reservoir Determined by Autoradiography and its Relationships to Phyto- and Zooplankton

In the drinking water reservoir Římov (Southern Bohemia) bacterioplankton was studied during 1983. Special attention was given to the relationships between parameters of bacterial abundance, total and individual activity. Bacterial counts and biomass was assessed and autoradiographic determinations of the proportion of active bacteria incorporating thymidine (Th) and mixture of amino acids (AA) and total uptake rate of AA were made over a year in the surface layer and during summer stratification from the thermocline and 15 m depth. Specific activity of metabolically active bacteria (SAMAB) and specific activity per unit of biomass (SAUB) were negatively correlated with counts of metabolizing cells and with bacterial biomass, respectively. Total and individual heterotrophic activity and counts of bacteria coincided with the changes of phytoplankton biomass, whereas bacteria incorporating Th were more tightly correlated with primary production. The most significant relation of metabolically active bacteria was found to cladoceran biomass. Thus, this part of heterotrophic bacterial activity seems to be stimulated by leakage of dissolved organic matter from phytoplankton being disrupted and incompletely digested by cladocerans rather than from healthy photosynthetizing cells.     

Microbiological Survey of Adirondack Lakes with Various pH Values

Nine high-altitude oligotrophic Adirondack lakes in upstate New York having water of pH 4.3 to 7.0 were surveyed for total bacterial numbers and possible adaptation of the microbial communities to environmental pH. The number of heterotrophic bacteria from water samples recoverable on standard plate count agar were low (10¹ to 10³ per ml) for most of the lakes. Acridine orange direct counts were approximately two orders of magnitude higher than plate counts for each lake. Sediment aerobic heterotrophs recovered on standard plate count agar ranged from 1.4 × 10⁴ to 1.3 × 10⁶ per g of sediment. Direct epifluorescence counts of bacteria in sediment samples ranged from 3.0 × 10⁶ to 1.4 × 10⁷ per g. Low density values were consistent with the oligotrophic nature of all the lakes surveyed. There were no apparent differences in numbers of bacteria originally isolated at pH 5.0 and pH 7.0 between circumneutral lakes (pH > 6.0) and acidic lakes (pH < 5.0). Approximately 1,200 isolates were recultured over a range of pH from 3.0 to 7.0. Regardless of the original isolation pH (pH 5.0 or pH 7.0), less than 10% of the isolates grew at pH < 5.0. Those originally isolated at pH 5.0 also grew at pH 6.0 and 7.0. Those originally isolated at pH 7.0 preferred pH 7.0, with 98% able to grow at pH 6.0 and 44% able to grow at pH 5.0. A chi-square contingency test clearly showed (P < 0.005) that two distinct heterotrophic populations had been originally isolated at pH 5.0 and pH 7.0, although there is undoubtedly some overlap between the two populations.     

Oligotrophic bacteria in ultra-pure water systems: Media selection and process component evaluations

Summary Presently, tryptic soy agar (TSA) medium is used in the semiconductor industry to determine the concentration of viable oligotrophic bacteria in ultra-pure water systems. Deionized water from an ultra-pure water pilot plant was evaluated for bacterial growth at specific locations, using a non-selective medium (R2A) designed to detect injured heterotrophic as well as oligotrophic bacteria. Results were compared to those obtained using Tryptic Soy Agar. Statistically greater numbers of bacteria were observed when R2A was used as the growth medium. Total viable bacterial numbers were compared both before and after each treatment step of the recirculating loop to determine their effectiveness in removing bacteria. The reduction in bacterial numbers for the reverse osmosis unit, the ion exchange bed, and the ultraviolet sterilizer were 97.4%, 31.3%, and 72.8%, respectively, using TSA medium, and 98.4%, 78.4%, and 35.8% using R2A medium. The number of viable bacteria increased by 60.7% based on TSA medium and 15.7% based on R2A medium after passage of the water through an in-line 0.2-m pore size nylon filter, probably because of the growth of bacteria on the filter. Our results suggest that R2A medium may give a better representation of the microbial water quality in ultra-pure water systems and therefore a better idea of the effectiveness of the various treatment processes in the control of bacteria.     

Lysogeny and lytic viral production during a bloom of the cyanobacterium Synechococcus spp

Lytic viral production and lysogeny were investigated in cyanobacteria and heterotrophic bacteria during a bloom of Synechococcus spp. in a pristine fjord in British Columbia, Canada. Triplicate seawater samples were incubated with and without mitomycin C and the abundances of heterotrophic bacteria, cyanobacteria, total viruses and infectious cyanophage were followed over 24 h. Addition of mitomycin C led to increases in total viral abundance as well as the abundance of cyanophages infecting Synechococcus strain DC2. Given typical estimates of burst size, these increases were consistent with 80% of the heterotrophic bacteria and 0.6% of Synechococcus cells being inducible by the addition of mitomycin C. This is the highest percentage of lysogens reported for a natural microbial community and demonstrates induction in a marine Synechococcus population. It is likely that the cyanophage production following the addition of mitomycin C was much higher than that titered against a single strain of Synechococcus; hence this estimate is a minimum. In untreated seawater samples, lytic viral production was estimated to remove ca. 27% of the gross heterotrophic bacterial production, and a minimum of 1.0% of the gross cyanobacterial production. Our results demonstrate very high levels of lysogeny in the heterotrophic bacterial community, outside of an oligotrophic environment, and the presence of inducible lysogens in Synechococcus spp. during a naturally occurring bloom. These data emphasize the need for further examination of the factors influencing lytic and lysogenic viral infection in natural microbial communities.