Yoshihiko Hata

Killing of marine phytoplankton by a gliding bacterium Cytophaga sp., isolated from the coastal sea of Japan

A marine gliding bacterium Cytophaga sp. (strain J18/M01) was isolated from Harima-Nada, eastern Seto Inland Sea, Japan in 1990. This bacterium preys upon various species of marine phytoplankton. All of the five raphidophycean flagellates, all of the four diatoms, and one of the two dinoflagellates examined were killed within a few days when cultured with the bacterium. The bacterium presumably achieves this by direct attack, because the culture filtrate in which host organisms were totally destroyed had no significant effects on the growth of the same host organism (Chattonella antiqua). If one or a few bacterial cells were inoculated into C. antiqua culture, all of the host organisms were killed. The bacterium proliferated in filter-sterilized seawater, suggesting its ubiquitous existence in the coastal sea. The killing of phytoplankton by bacteria such as Cytophaga sp. J18/M01 may be a significant factor influencing the population dynamics of phytoplankton in nature and may contribute to the sudden disappearance of red tides in the coastal sea. Bacterial destruction of phytoplankton may also be a factor that regulates primary productivity in marine ecosystems.

Gymnodinium nagasakiense赤潮の発生・消滅に関与する細菌の分布とその効果

Marine bacteria are one of the most influential organisms on the growth of microalgae in seawater and their effects are either stimulative1-4) or inhibitory.5,6) However, very little information is available on the bacterial behavior during the development or the decay7) of a phytoplankton blooming (red tide), although they should play a significant role during the algal blooms. Red tide can be considered to be an explosive growth of one or a few selective species of phytoplankton among the usual flora and as the succession of dominant species of plankton. It is therefore important to clarify the effect of bacteria on the development and the decline of red tide and on the succession of phytoplankton species predominating for the prediction and the prevention of red tide. Riquelme et al.8) reported that a specific Pseudomonad bacterium increased prior to the development of a bloom of a diatom Asterionella glacialis in Maizuru Bay and that this bacterium produced a glycoprotein as a growth factor for A. glacialis.9) They demonstrated the close relationship between the bacterium and the alga.8,10) However, the inhibitory effect of a bacterium on the decline of phytoplankton bloom has neither yet clarified nor elucidated the influence of the bacteria effective on one species of plankton on the growth of the other species. G. nagasakiense Takayama and Adachi (Dinophyceae)11) is one of the most noxious phytoplanktons causing mass mortalities of fish culture in a western region of Japan,12) although it is said up to now that it has no effective toxicity.13) We have frequently had heavy red tides consisting of G. nagasakiense in Uranouchi Inlet in Kochi and serious damage has often been caused from the end of June through July. Although many studies have been carried out on the physiology of the growth of G. nagasakiense14-17) and on many physico-chemical environmental factors such as temperature, light intensity, inorganic nutrient and others, the mechanism of the

Distribution of thiamine, biotin, and vitamin B12 in lake Kojima. II. Distribution in the bottom sediments.

In the previous report, concentrations of thiamine, biotin, and vitamin B12 in the water of Lake Kojima, a eutrophic lake, were shown to be fairly high. In the present paper, contents of these B group vitamins in the bottom sediments of Lake Kojima which were determined by microbiological assay methods are reported. Also the relations between vitamin contents and some chemical or biological environmental factors are described.

Kinetic study of vitamin B12 production and consumption in natural seawater.

Kinetics for the production and consumption of vitamin B12, by the natural microbial community in a coastal seawater were analyzed, and their contribution to production and consumption is discussed.The total consumption rate for vitamin B12 of natural bacterial and phytoplankton communities was 4.85ng/l/day in the dark and ranged from 6.10 to 6.41 ng/l/day in the light. The contribution of the bacterial community to the total light vitamin B12 consumption was about 50-59% and the remains were due to the phytoplankton community. The half-saturation constant for vitamin B12 uptake of phytoplankton (larger than 5μm) were 0.2-0.3 ng/l in the light, and those of bacteria were 0.17-0.48 ng/l. The in situ vitamin B12 uptake rate of both communities were found to he almost saturated at the naturally occurring concentration of vitamin B12.The gross production rate for vitamin B12 of both communities totaled 5.32ng/l/day in the dark and 6.04-6.45ng/l/day in the light, and the bacterial community contributed about 73% to the total in the dark and about 63% in the light. Thus, the total vitamin B12 gross production rate of both communities was almost equal to their total consumption rate. The bacterial community produced vitamin B12 in excess to the amount they consumed, but the phytoplankton community only produced vitamin B12 in quantities less than the amount they consumed.Consequently, both bacterial nad phytoplankton communities were found to contribute greatly to both production and consumption of dissolved vitamin B12 in eutrophic coastal seawaters.