Two Trophic Groups of Bacteria, Oligotrophs and Eutrophs: Their Distributions in Fresh and Sea Water Areas in the Central Northern Japan

Abstract

Two groups of bacteria were determined as oligotrophs and eutrophs. The former can grow only on a poor medium and not on a rich medium, and the latter can grow on a rich medium. Based on such trophic nature of bacterial groups, a method was established for counting viable cell number of oligotrophs and eutrophs, employing poor and rich media. The present method was used to examine water samples of fresh and sea water areas including rivers and lakes in Toyama Prefecture, off the coast of Toyama Bay, and open sea area at Yamato Bank in the Japan Sea. Physical and chemical environmental factors in these areas were also estimated. Based on the result of an extensive survey on these oligotrophic and eutrophic water samples, two general conclusions were deduced: (a) Oligotrophs and eutrophs responded quite similarly to respective chemical environmental factors, and (b) the number of these trophic groups remained almost constant at even higher concentrations of these factors. In fresh water areas, the number of oligotrophs usually exceeded that of eutrophs, and limiting substances for the size of these bacterial populations were considered to be nitrate-nitrogen and dissolved organic nitrogen. From the effect of rainfall on the number and trophic flora of bacteria in a river, the source of river bacteria was suggested at least in part to be attributed to the soil bacteria.In conventional studies on emphasis has been laid on some microorganisms in a natural water system, extreme living conditions specific to water an en-

Oligotrophy and pelagic marine bacteria: facts and fiction

“…The method therelore did not ensure oligoti-ophic conditions throughout the experiment and the result should be interpreted accordingly. Yanagita et al (1978) used approximately the same filter method and found similar results. In any case, if oligotrophic bacteria exist as a dominant population in seawater, their growth will effectively be suppressed at 16.8 mg peptone-C 1-' using such procedures.…”

“…The isolation of obligate oligotrophs has been claimed by several authors (Yanagita et al 1978, Ishida & Kadota 1981, Fry 1990). Ishida & Kadota (1981) obtained 18 obligate oligotrophs from lake water that could not grow on an agar surface.…”

“…Some researchers define oligotrophs as organisms able to grow at nutrient concentrations of 5 mg C 1-' but not at concentrations of 7.5 g C 1-' (Yanagita et al 1978). Others define oligotrophs as those bacteria that are able to grow on media with 1 to 15 mg C 1-' as well as on media with a higher nutrient content (Kuznetsov et al 1979).…”

“…oligotroph~c micro-organisms are prokaryotic and eukaryotic organisms that are evolutionarily adapted to exploit ecological niches characterised by low substrate concentrations and low energy fluxes. Oligotrophs, [...l Fry (1990) Semenov (1991 (see also Yanagita et al 1978), as opposed to obligate oligotrophs that cannot grow at substrate concentrations above 0.3 g C 1-l. Horowitz et al (1983) postulated the term euryheterotroph for facultative oligotrophic bacteria and Baxter & Sieburth (1984) replaced 'facultative oligotroph' by 'eurytroph'. The confusion on the proper definition is strengthened by the fact that some researchers use the term oligotroph only for those organisms that are restricted to growth on low nutrient media, while others employ the term to broadly speak about both the obligate and facultative oligotrophs.…”

“…In aquatic microbiology, Winogradsky's division was adopted with slight modifications in terminology over the years. Zymogenous bacteria are currently called 'copiotrophs' (Poindexter 1981, Fry 1990, which is analogous to 'saprophytes' (Kuznetsov et al 1979), 'eutrophs' (Yanagita et al 1978, Martin & MacLeod 1984, Ishida et al 1986) and 'heterotrophs' (Akagi et al 1980). Autochthonous bacteria are called 'oligotrophs' (Poindexter 1981, Fry 1990, although 'oligocarbophiles' (Moaledj 1978), 'low-nutrient (LN) bacteria' (Carlucci & Shimp 1974), 'low K, bacteria' (Baxter & Sieburth 1984) or 'DNB (dilute nutrient broth) organisms' (Kasahara & Hattori 1991) may also be encountered in the literature.…”