Studies on Planktonic Bacteria by Means of a Direct Membrane Filter Method

Abstract

SUMMARY: Direct observations on the occurrence and spatial distribution of planktonic bacteria were made by using a membrane filter technique. The membrane filters were treated to allow direct microscopic examination of bacteria on their surfaces. Deviations between direct counts on the membranes and plate (colony) counts of bacteria depended upon availability of organic matter in the natural waters studied, and can be accounted for by clumping effects and the occurrence of very small forms not visible on the membrane filter surfaces. Indirect evidence for these 'dwarf' forms was provided by later development of colonies with cells of normal size, after the membrane filter was placed on a nutrient medium. This response suggests that the organisms are zymogenous forms. Pure cultures of Bacillus subtilis and Pseudomonas Jluorescens were used in some experiments to demonstrate the relationship between the clumping effect and concentration of dissolved nutrients in water. A concentration of 0-5 mg. peptonell. in a tap-water medium caused accumulations of bacteria around clean chitin particles ; accumulations of bacteria did not develop at the higher concentrations tested. This behaviour is explained by the local differences in concentrations of nutrients in the medium. It correlates with the observations on natural populations.The nutritional factor determines not only the distribution of bacteria in natural waters, but also the methods available for their demonstration. Only enriched substrates yield readily measurable bacterial growth and metabolic products in laboratory cultures as well as in nature. The lack of direct indicators of quantity of bacterial growth in media very poor in nutrients may have been a cause for much more work being done on the bacteria of bottom deposits of natural waters as compared to the planktonic forms.In uncontaminated natural waters the concentration of dissolved organic matter is generally low, but when suitable solid or colloidal organic matter is present, individual bacteria may be confronted with higher concentrations of nutrients. By means of largely unknown and complex adjustments, natural populations of bacteria are able to decompose organic compounds over a wide range of concentration and composition. I n the same way that bacterial populations adjust to natural conditions, they adjust to artificial conditions of cultivation. Consequently, it is impossible to determine their original activity after transfer to a medium enriched in nutrients. This means of increasing the formation of reaction products is integral to most of the general methods of estimating the quantity of bacteria. If any process is involved whereby metabolism is promoted, the method should be defined as indirect and the results applied with caution to ecological problems (Gibson, 1957). The

Detection of abundant bacteria in the Weser estuary using culture-dependent and culture-independent approaches

“…much less than 1%, of the natural bacterioplankton community enumerated by light or epifluorescence microscopy can be cultivated, preferentially on solid media (Razumov 1932, Jannasch 1958, Kuznetsov 1975, Staley & Konopka 1985, Eguchi & Ichida 1990. During the 1970s and 1980s, increasing evidence accumulated that the major fraction of the as yet uncultured bacteria actively grows and participates in the flux of energy and cycling of nutrients in aquatic ecosystems (van Es & Meyer-Reil 1982, Cole et al 1988.…”

The relationship between planktonic algae and bacteria in a small lake

“…However, a general medium such as the Oxoid nutrient agar should give maximum results (Overbeck, 1965) . These results probably underestimate the total numbers of bacteria present (Kuznetsov & Karzinkin, 1931, Waksman, 1934Jannasch, 1953Jannasch, , 1958Jannasch, , 1963Jannasch, , 1967Kuznetsov, 1959;Prokesova, 1963 andWood, 1967 Generally, a large algal population was invariably correlated with an increase in bacterial numbers as found by other workers (Overbeck, 1965(Overbeck, , 1967(Overbeck, , 1968Overbeck & Barbenzien, 1964 ;Anagnostidis, andOverbeck, 1966, Olah, 1971) . This was particularly true with the aerobic bacteria .…”

The Antibacterial Activity of Marine Planktonic Algae

“…I t will be appreciated that these findings result from the effect of concentrated algal extracts diffusing through a gel, a circumstance very different from those apparently existing under natural conditions. However, as bacteria are frequently found attached to or adsorbed upon various surfaces in the marine environment (Jannasch 1958), our findings may have a bearing on the ecological control of epiphytic bacteria by phytoplankton blooms. Such control and regulation of the epibiota by antibiotics diffusing outwards from the thallus of some macroscopic algae or from the cells of some planktonic algae is indicated by several examples cited by Sieburth (1964).…”