Depth‐related changes in whole‐community structure were evaluated in a coastal marine sediment using a molecular fingerprinting method, terminal restriction fragment length polymorphism (T‐RFLP) analysis, and a chemotaxonomic technique (quinone profiling). Dendrograms derived from both T‐RFLP analysis and quinone profiling indicated a significant variation in microbial community structure between the 0–2 cm layer and deeper layers. This corresponded to the dramatic change in the redox potential, acid‐volatile sulphide‐sulphur and bacterial numbers observed at 0–2 cm and 2–4 cm depths. A significant change in the number of terminal restriction fragments (T‐RFs) was also detected at this transition depth. However, the change in major T‐RFs with depth was not seen in electropherograms. The population changes were primarily variations in minor ribotypes. Most quinone homologues were detected at all depths, although the quinone composition changed with depth. Therefore, quinone profiling also suggested that the depth‐related variation was primarily attributable to minor bacterial groups rather than change in the major population structure. 16S rDNA clone library analysis revealed that clones belonging to the genera Vibrio and Serratia predominated as major bacterial groups at all depths. Our data suggested that the sediment community might result from sedimentation effects of sinking particles. Overall, our results demonstrated that the combined methods of T‐RFLP analysis and quinone profiling were effective for assessing depth‐related microbial populations
Ecological survey of yeasts was conducted during the cruise of KH-67-5, by the research vessel Hakuho-Maru of Ocean Research Institute, University of Tokyo, along Long. 150°E from Lat. 44°N to the equator in the Pacific Ocean in December, 1967. Yeasts were detected from the surface to a depth of 4, 000m. Of 184 seawater samples, 27.7% were positive for yeasts. The average number of yeasts detected in 1 liter of seawater was 56.7 for yeast-positive samples and 15.7 for total samples.Isolated yeast strains were identified as strains belonging to the genera of Rhodotorula, Cryptococcus, Debaryomyces, and Candida.The effects of salt concentration, temperature, pH, and hydrostatic pressure on the growth of selected strains were studied for the assessment of the possibility whether the reproduction of marine-occurring yeasts is actual or not in the environment in situ. Maximum NaCl tolerance ranged from 9 to 21%, exhibiting fairly good growth at NaCl concentration of seawater. The pH threshold for growth on alkaline range overlapped with the pH range of seawater. The pH 8.1, a widely observed pH in the sea, was deleterious for most of the strains. It was suggested that marine yeasts may be subjected to extensive pH effects by different bodies of seawater. The maximum tolerance to increased hydrostatic pressure observed among the strains was 400 to 500 atm, which corresponds to a depth of 4, 000 to 5, 000m. It was suggested from the pressure experiments that for the growth of most marine yeasts hydrostatic pressure is not so exacting until the depth reaches 2, 000m, and its adverse effect increases with depth and are remarkable at the depth of 4, 000m or more. Though marine-occurring yeasts seemed to be more tolerant to hydrostatic pressure than terrestrial yeasts, no clear relationship could be found between the tolerance and the depth from which they were isolated.
A flow cytometer was used to measure the intracellular RNA contents of Vibrio alginolyticus and natural bacterial populations after specific staining with acridine orange. During the course of starvation, the RNA level in Vibrio alginolyticus gradually decreased, whereas subsequent enrichment caused a rapid increment of RNA and resulted in the appearance of a distinct group on the cytometric histogram. Similar distinct subpopulations were also confirmed in natural seawater samples after 6 hours direct viable count (DVC) incubation. Moreover, it was confirmed that the DVC technique enabled us to detect and enumerate marine bacteria using 16S rRNA fluorescent oligonucleotide probes.
