Direct Bacterial Counts Research Articles

Elevated levels of microbial activity in the coral surface microlayer

Mcrobial biomass and activity parameters were measured in the mucus-rich, coral surface microlayer (CSM) and in the waters overlying coral reefs in the Dry Tortugas and Key West Florida, USA. For all parameters measured (thymidine ~ncorporation, bacterial direct counts, primary production, chlorophyll a, dissolved DNA, and particulate DNA), the CSM values were significantly greater than the overlying water values on a per volume basis. Enrichment in the CSM ranged from nearly equal to 7.5-fold for bacterial direct counts to 18 to 280-fold for chlorophyll a. Microautotrophic processes in the CSM were due almost exclusively to the activities of free-living zooxanthellae, while activities in overlying waters were dominated by autotrophic picoplankton. Higher cellular rates of thymldine incorporation (1.23 to 50 tlmes greater) indicated that bacteria in the CSM were growing faster than those in the water column. Bacterial production estimates on a per area basis in the CSM (thickness = several mm) were equivalent to that of the whole water column over the reef (depth 1 to 4 m). Size fractionation of the CSM indicated that most of this bacterial activity was associated with particles > l pm, while overlying waters were dominated by <l pm, free-living bacterioplankton. No significant temporal or spatial variation was noted In these parameters in the overlying waters in a transect across the reef or in a die1 study. However, all values in the CSM (except direct counts) were significantly greater at a midnight sampling than at a noon samphng. Dissolved deoxyribonuclease activity was found in both environments. Collectively these results indicate that the CSM contains an extremely active microbial community, comparable to that found in a eutrophic estuary. These results are discussed in terms of reef production in oligotrophic environments and nutrient dynamics.

Particulate DNA in subtropical oceanic and estuarine planktonic environments

Particulate DNA was measured in estuarine, coastal, and oligotrophic oceanic environments near the southwest coast of Florida and in the Gulf of Mexico. Particulate organic carbon and nitrogen (POC and PON), chlorophyll a, bacterial direct counts, DNA, and bacterial activity as determined by thymidine incorporation all showed a high degree of intercorrelation. Normalization of the data for offshore/onshore similarities by dividing by POC yielded significant correlations only for DNA, direct counts, and bacterial activity. Most (70–99%) of the particulate DNA in offshore samples was in the 0.2- to 1-μm fraction, while DNA in nearshore and estuarine samples was associated with larger particles. Cellular DNA contents obtained by dividing DNA by direct counts in the 0.2- to 1-μm fraction were in the range of reported bacterial genome weights. However, DNA nitrogen comprised a greater proportion of the PON than reported for microorganisms in culture. Collectively, these results suggest that (1) most of the particulate DNA in oceanic environments is contained in bacterioplankton; (2) DNA is a significant proportion of the cell biomass, possibly due to growth under nutrientlimiting conditions.

Characteristics of some fermentative bacteria from a thermophilic methane-producing fermenter

Anaerobic bacteria from a 55‡C methane-producing beef waste fermenter were enumerated, isolated, and characterized. Direct microscopic bacterial counts were 5.2-6.8×10(10) per g fermenter effluent. Using a nonselective roll-tube medium which contained 40% fermenter effluent, 8.5-14.1% of the microscopic count was culturable. Deletion of fermenter effluent significantly reduced the viable count. Sixty-four randomly picked strains were characterized. All were pleomorphic, gram-negative, anaerobic rods, many of which were difficult to grow in liquid media. The strains were divided into 5 major groups based on glucose fermentation, hydrogen sulfide production, starch hydrolysis, fermentation products, and morphology. Glucose was fermented by 75% of the isolates, 76% utilized starch, 25% produced hydrogen sulfide, 76% produced hydrogen, 37% produced indole, 21% hydrolyzed gelatin, and 13% were sporeformers. Ethanol, lactate, formate, acetate, and hydrogen were common fermentation products. Twenty-four representative strains had 1-12 flagella. Growth was observed between 35 and 73‡C. These studies indicate that species diversity among the isolated organisms was low.

Effect of severe dehydration and rapid rehydration on the activity of the rumen microbial population of black Bedouin goats

SUMMARYDrinking regimes of Bedouin goats affect their feeding behaviour and the ruminal environmental conditions, as expressed by changes in osmotic pressure as well as in pH of the rumen content. The osmotic concentration of the rumen content of a goat drinking once daily was 330 m-osmole/kg just before drinking. After water deprivation for 4 days, the osmotic concentration reached 360 m-osmole/kg and, immediately after excessive drinking, decreased to 82 m-osmole/kg. After a short while, the osmotic concentration increased to 300 m-osmole/kg and after 13 h reached the peak of 440 mosmole/kg, mainly owing to the release of degradation products. The pH was also affected by food consumption. Just prior to drinking, the pH in the rumen of dehydrated goats was 6·9. It decreased to 6·0 after excessive drinking and feeding. Later, it ranged between 6·4 and 7·1.Most of the micro-organisms in the rumen are attached to the fibres fraction. No difference could be observed in direct bacterial counts in the fluid fraction between dehydrated and goats drinking daily. However, the number of protozoa was reduced in dehydrated goats, especially after excessive drinking, as some species of protozoa seem to explode in a hypo-osmotic ambient.The fermentation capacity of the fibres fraction was higher than that of the fluid fraction, indicating also the presence of more micro-organisms in the fibres. In addition, the osmotic changes occurring during the dehydration-rehydration cycles had no significant effect on fermentation capability of the rumen micro-organisms.At a low osmotic concentration in an NaCl deficient ambient, there was some decrease in fermentation rate, but this could be nullified with the addition of NaCl, which is required for microbial activity. The decrease in fermentation rate is not due to its effect on the osmotic concentration. The micro-organisms in the fibres fraction were found to be less affected by NaCl deficiency in the ambient medium.

USE OF A SPECIFIC‐ION ELECTRODE (AMMONIA) IN DETERMINING THE QUALITY OF SHRIMP

ABSTRACTAmmonia and other volatile nitrogen compounds are major components of the off‐flavors and odors associated with spoiled shrimp. Increases in the level of total volatile nitrogen (TVN) have been used as an objective index of shrimp quality. In order to find a simple method for determining shrimp quality the use of an ammonia specific‐ion electrode was investigated. Ammonia produced from both iced and noniced refrigerated shrimp together with direct microscopic bacterial counts, TVN and sensory evaluation were measured as a function of storage time. The results indicated a close correlation between ammonia, as measured by the specific‐ion electrode, and the more traditional spoilage parameters. Frozen shrimp with various pre‐frozen spoilage characteristics were also evaluated using the ammonia specific electrode. Although a correlation was observed between the pre‐frozen spoilage characteristics and ammonia measured in the frozen shrimp, the data fluctuations using the ammonia specific electrode appeared too dramatic to infer spoilage characteristics prior to freezing. The use of the ammonia specific‐ion electrode is a rapid and simple method for determining shrimp quality, especially in iced raw shrimp, and possibly of significant value in the shrimp industry's quality control efforts.

Frequency of Dividing Cells, a New Approach to the Determination of Bacterial Growth Rates in Aquatic Environments

Frequency of dividing cells is suggested to be an indirect measure of the mean growth rate of an aquatic bacterial community. Seasonal changes in frequency of dividing cells were found which covariated with the bacterial uptake of C-labeled phytoplankton exudates. Batch and continuous culture growth experiments, using brackish water bacteria in pure and mixed enrichment cultures, were performed to establish a relationship between frequency of dividing cells and growth rate. An improved technique for bacterial direct counts, using fluorescent staining and epifluorescence microscopy, is presented. Based on a 6-month survey in a coastal area of the Baltic Sea, the bacterial production in the photic zone is estimated. Compared to the total primary production in the area, the bacterial population during this period utilized approximately 25% of the amount of carbon originally fixed by the primary producers.

Solar Lake (Sinai). 3. Bacterial distribution and production1

The relations between photosynthetic and nonphotosynthetic (chemoorganotrophic and chemolithotrophic) microorganisms in Solar Lake were studied during the annual limnological cycle. Six different bacterial plates were observed during stratification by direct and viable bacterial counts, light and dark CO2 incorporation, chlorophyll a, protein, ATP, and ETS determinations. A maximal dark CO2 incorporation of 1,014 mg C m−3 d−1 may represent as much as 16,900 mg C m−3 d−1 of chemoorganotrophic bacterial production, on the assumption that these bacteria assimilate an average of 6% CO2 of their total carbon uptake. This calculated production is very high in comparison to the recorded photosynthetic maximum of 4,960 mg C m−3 d−1. The organic carbon needed for such a high chemoorganotrophic production may be supplied by the benthic cyanobacterial mats. Extremely high specific activities of ATP and ETS for the layer immediately above the thermocline indicate a very active bacterial plate at this layer.

Antibiotic treatment of lake sediments to determine the effect of fungi on decomposition

To determine the role of fungi in decomposition, sediment from a eutrophic lake and a bog was treated with antibacterial antibiotics or with antifungal antibiotics. Sediment treated with antibacterial antibiotics showed a decrease in biochemical oxygen demand and a decrease in direct and pour-plate bacterial counts when compared with controls. Sediment treated with antifungal antibiotics showed an increase in biochemical oxygen demand and an increase in pour-plate and direct bacterial counts when compared with controls. Two species of lake fungi inhibited the growth of a mixed culture of lake bacteria on agar plates. The results infer that fungi inhibit the growth of bacteria in aerobic lake sediment.

Direct bacterial count as a rapid freshness test for fish fillets.

Comparison of various indices of deterioration of refrigerated fish fillets showed that the direct bacterial count can be used to predict the storage life of the foodstuff. For direct counts, a thin film made from fillet surface material was spread on a microscope slide, stained, and read. Initial counts were found to correlate well with keeping quality; a period of freshness of 24 or 48 hr at 5 C could be reliably predicted. Preliminary data indicated that hypoxanthine estimation could probably also be used for the prediction of shelf life but that the relative complexity of the procedure detracted from its usefulness.

Direct Bacterial Count as a Rapid Freshness Test for Fish Fillets

Comparison of various indices of deterioration of refrigerated fish fillets showed that the direct bacterial count can be used to predict the storage life of the foodstuff. For direct counts, a thin film made from fillet surface material was spread on a microscope slide, stained, and read. Initial counts were found to correlate well with keeping quality; a period of freshness of 24 or 48 hr at 5 C could be reliably predicted. Preliminary data indicated that hypoxanthine estimation could probably also be used for the prediction of shelf life but that the relative complexity of the procedure detracted from its usefulness.

Rise and Fall of Bacterial Populations in Fish Muscle

A direct bacterial count method applicable to fish muscle containing over approximately 1 × 105 bacteria per gram, with a modification employing preliminary incubation for muscle containing fewer bacteria, is described. Direct counts generally yielded similar and somewhat higher results than viable counts. Mixed bacterial populations of fish muscle generally exhibited the growth phases characteristic of a pure bacterial culture. There was absolutely no relation between direct (or viable) counts obtained subsequent to such incubation and the initial viable counts of the samples studied. Bacteria increased much more rapidly in excised fish muscle than in whole fish, and somewhat more rapidly in halibut than in salmon flesh.