Recently developed techniques for estimating bacterial biomass and productivity indicate that bacterial biomass in the sea is related to phytoplankton concentration and that bacteria utilise 10 to 50 % of carbon fixed by photosynthesis. Evidence is presented to suggest that numbers of free bacteria are controlled by nanoplankton~c heterotrophic flagellates which are ubiquitous in the marine water column. The flagellates in turn are preyed upon by microzooplankton. Heterotrophic flagellates and microzooplankton cover the same size range as the phytoplankton, thus providing the means for returning some energy from the 'microbial loop' to the conventional planktonic food chain.

/pdf/the-ecological-role-of-water-column-microbes-in-the-sea-34dv8tiwzr.pdf

The Ecological Role of Water-Column Microbes in the Sea*

There is an urgent need in aquaculture to develop microbial control strategies, since disease outbreaks are recognized as important constraints to aquaculture production and trade and since the development of antibiotic resistance has become a matter of growing concern. One of the alternatives to antimicrobials in disease control could be the use of probiotic bacteria as microbial control agents. This review describes the state of the art of probiotic research in the culture of fish, crustaceans, mollusks, and live food, with an evaluation of the results obtained so far. A new definition of probiotics, also applicable to aquatic environments, is proposed, and a detailed description is given of their possible modes of action, i.e., production of compounds that are inhibitory toward pathogens, competition with harmful microorganisms for nutrients and energy, competition with deleterious species for adhesion sites, enhancement of the immune response of the animal, improvement of water quality, and interaction with phytoplankton. A rationale is proposed for the multistep and multidisciplinary process required for the development of effective and safe probiotics for commercial application in aquaculture. Finally, directions for further research are discussed.

/pdf/probiotic-bacteria-as-biological-control-agents-in-4778jdx241.pdf

Probiotic Bacteria as Biological Control Agents in Aquaculture

The measurement of lipid phosphate is proposed as an indicator of microbial biomass in marine and estuarine sediments. This relatively simple assay can be performed on fresh, frozen or frozen-lyophilized sediment samples with chloroform methanol extraction and subsequent phosphate determination. The sedimentary lipid phosphate recovery correlates with the extractible ATP and the rate of DNA synthesis. Pulse-chase experiments show active metabolism of the sedimentary phospholipids. The recovery of added 14C-labeled bacterial lipids from sediments is quantitative. Replicate analyses from a single sediment sample gave a standard deviation of 11%. The lipid extract can be fractionated by relatively simple procedures and the plasmalogen, diacyl phospholipid, phosphonolipid and non-hydrolyzable phospholipid content determined. The relative fatty acid composition can be readily determined by gas-liquid chromatography. The lipid composition can be used to define the microbial community structure. For example, the absence of polyenoic fatty acids indicates minimal contamination with benthic micro-eukaryotes. Therefore the high content of plasmalogen phospholipids in these sediments suggests that the anaerobic prokaryotic Clostridia are found in the aerobic sedimentary horizon. This would require anaerobic microhabitats in the aerated zones.

Determination of the sedimentary microbial biomass by extractible lipid phosphate.

Heterotrophic bacteria are thought to be important components of aquatic ecosystems in several ways. These bacteria remineralize organic materials and convert some organic material into bacterial biomass. We examined data from 70 studies in which estimates of production of heterotrophic bacterial biomass (bacterial production) were reported for freshand saltwater ecosystems. In sediments, bacterial production was sigdicantly (p <0.001), positively correlated to sediment organic C content. Systems which had hlgh rates of benthic primary production (such as coral reefs) had rates of bacterial production greater than those predicted by sediment organic C content alone. In the photic zone of lakes and the ocean, bacterial production was significantly correlated with planktonic primary production, chlorophyll a, or numbers of planktonic bacteria. For all planktonic systems analysed, bacterial production ranged from 0.4 to 150 pg C 1-' d-' and averaged 20 % (median 16.5 %) of planktonic primary production. On an area1 basis for the entire water column, bacterial production ranged from 118 to 2439 mg m-2 d-' and averaged 30 % (median 27 %) of water column primary production. Heterotrophic bacterial production is, thus, a large component of total secondary production and is roughly twice as large as the production of macrozooplankton for a given level of primary production.

/pdf/bacterial-production-in-fresh-and-saltwater-ecosystems-a-3058k94tmt.pdf

Bacterial production in fresh and saltwater ecosystems: a cross-system overview

Heterotrophic bacteria perform two major functions in the transformation of organic matter: They produce new bacterial biomass (bacterial secondary production [BP]), and they respire organic C to inorganic C (bacterial respiration [BR]). For planktonic bacteria, a great deal has been learned about BP and its regulation during the past several decades but far less has been learned about BR. Our lack of knowledge about BR limits our ability to understand the role of bacteria in the carbon cycle of aquatic ecosystems. Bacterial growth efficiency (BGE) is the amount of new bacterial biomass produced per unit of organic C substrate assimilated and is a way to relate BP and BR: BGED (BP)=(BPC BR). Estimates of BGE for natural planktonic bacteria range from <0.05 to as high as 0.6, but little is known about what might regulate this enormous range. In this paper we review the physiological and ecological bases of the regulation of BGE. Further, we assemble the literature of the past 30 years for which both BP and BR were measured in natural planktonic ecosystems and explore the relationship between BGE and BP. Although the relationship is variable, BGE varies systematically with BP and the trophic richness of the ecosystem. In the most dilute, oligotrophic systems, BGE is as low as 0.01; in the most eutrophic systems, it plateaus near 0.5. Planktonic bacteria appear to maximize carbon utilization rather than BGE. A consequence of this strategy is that maintenance energy costs (and therefore maintenance respiration) seems to be highest in oligotrophic systems.

/pdf/bacterial-growth-efficiency-in-natural-aquatic-systems-3h512vpf8i.pdf

Bacterial growth efficiency in natural aquatic systems

Control of luminous Vibrio species in penaeid aquaculture ponds

http://www.protocol-online.org/forums/uploads/monthly_08_2009/msg-7000-1249573136.ipb

The role of microorganisms in aquaculture ponds

The cells of blue‐green algae are lysed by high concentrations of acid (pH 1.9–1.4) in the stomach of Tilapia nilotica. After lysis, cell contents are digested in the intestine. Acid secretion follows a diurnal cycle related to feeding, and thus there is a cycle from zero to maximum digestion each day. Some of the digestive enzymes have been studied. Blue‐green algae are lysed by a high concentration of acid in the stomach. pH 1.4 is the lowest value recorded in the stomach of T. nilotica; lysis is most effective at this pH. Enzymatic digestion occurs in the intestine, after the algae are lysed. Acid secretion in the stomachs of T. nilotica and H. nigripinnis in Lake George, Uganda, follows a diurnal cycle associated with feeding. Secretion starts when feeding starts in the morning. In T. nilotica, low pH values are not obtained throughout the stomach until feeding ceases in the evening. Thus there is a gradation through the day, from zero to maximum in number of blue‐green algal cells lysed, and therefore digested and assimilated. Colour changes in the ingested phytoplankton can be used as an indicator of gastric acid secretion by fish in the laboratory. Acid is not secreted by stressed fish. Pepsinogen was detected in the stomach wall of T. nilotica. Evidence for the absence of peptic digestion in the stomach of T. nilotica is presented. A pancreatic α‐amylase, pH optimum 7.0 to 8.0, and requiring chloride, is present in the intestinal juice of T. nilotica. Trypsin and chymotrypsin are also present, but carboxypeptidases A and B could not be detected. Esterase activity, but no lipase, was detected in the intestine juice. 1973 The Zoological Society of London

The physiology of digestion of blue‐green algae in the cichlid fish, Tilapia nilotica

The rate of tritiated thymidine incorporation into DNA was used to estimate bacterial growth rates in aquatic environments. To be accurate, the calculation of growth rates has to include a factor for the dilution of isotope before incorporation. The validity of an isotope dilution analysis to determine this factor was verified in experiments reported here with cultures of a marine bacterium growing in a chemostat. Growth rates calculated from data on chemostat dilution rates and cell density agreed well with rates calculated by tritiated thymidine incorporation into DNA and isotope dilution analysis. With sufficiently high concentrations of exogenous thymidine, de novo synthesis of deoxythymidine monophosphate was inhibited, thereby preventing the endogenous dilution of isotope. The thymidine technique was also shown to be useful for measuring growth rates of mixed suspensions of bacteria growing anaerobically. Thymidine was incorporated into the DNA of a range of marine pseudomonads that were investigated. Three species did not take up thymidine. The common marine cyanobacterium Synechococcus species did not incorporate thymidine into DNA.

https://aem.asm.org/content/aem/48/6/1076.full.pdf

Validity of the tritiated thymidine method for estimating bacterial growth rates: measurement of isotope dilution during DNA synthesis.

Shrimp aquaculture production in much of the world is depressed by disease, particularly caused by luminous Vibrio and/or viruses. Antibiotics, which have been used in large quantities, are in many cases ineffective, or result in increases in virulence of pathogens and, furthermore, are cause for concern in promoting transfer of antibiotic resistance to human pathogens. Probiotic technology provides a solution to these problems. The microbial species composition in hatchery tanks or large aquaculture ponds can be changed by adding selected bacterial species to displace deleterious normal bacteria. Virulence of luminous Vibrio species can be controlled in this manner. Abundance of luminous Vibrio strains decreased in ponds and tanks where specially selected, probiotic strains of Bacillus species were added. A farm on Negros, in the Philippines, which had been devastated by luminous Vibrio disease while using heavy doses of antibiotics in feed, achieved survival of 80-100% of shrimp in all ponds treated with probiotics.

/pdf/disease-control-in-shrimp-aquaculture-with-probiotic-3vt0rx9414.pdf

David J. W. Moriarty

Papers

Control of luminous Vibrio species in penaeid aquaculture ponds

The role of microorganisms in aquaculture ponds

The physiology of digestion of blue‐green algae in the cichlid fish, Tilapia nilotica

Validity of the tritiated thymidine method for estimating bacterial growth rates: measurement of isotope dilution during DNA synthesis.

Disease Control in Shrimp Aquaculture with Probiotic Bacteria