JAMSTEC

Exploring of microbial diversity in the deep-sea environments

The most concentrated and widespread occurrences of organisms are generally in so-called "moderate" environments with approximately neutral pH, temperatures around 20-37°C, pressures near 0.1 MPa, and adequate concentrations of nutrients and saline. In contrast, the deep-sea is an extreme environment with especially high hydrostatic pressure and low temperature. Microorganisms living there presumably have developed particular characteristics that allow them to thrive at such an environment. Some bacteria have been isolated from deep-sea mud and from benthic organisms such as amphipods and sea cucumbers in the bathypelagic zone. However, little information is available on bacterial diversity in sediments of the deep-sea floor because most marine biologists have focused on barophilic and psychrophilic inhabitants of the deep-sea environment.

Latest topics

1. Microbial Diversity in the Deep-sea Environment

On 2 March, 1996, the 3 m long unmanned submersible Kaiko touched the bottom of the Challenger Deep in the Mariana Trench and successfully scooped out a mud sample, the first obtained at a depth of 10897 m. We attempted to isolate thousands of microorganisms from deep sea mud samples and benthic organisms collected at various depths of 1000 to 11000 m in order to characterize the microbial diversity in such an extreme environment. Various non-extremophilic bacteria were isolated from the mud sample collected even at a depth of 11000 m from the Mariana Trench with a frequency of 2.2 x 104 - 2.3 x 105 colonies per g dry sea mud under moderate culture conditions.

Collection of a mud sample at a depth of 10897 m from Challenger Deep. The white arrow shows the sampling tube holder (A). The white arrow head and open arrow head show a 50 ml Falcon tube and sample inlet, respectively (A,B, D). The deep-sea mud was scooped out by a manipulator as shown in alphabetical order (B, C, D)
Extremophilic bacteria such as alkaliphiles, thermophiles, and psychrophiles were also isolated with a frequency of 2.0 x 102 to 3.5 x 103 from the same deep sea mud. The total 16S rDNA sequences of deep-sea isolates were determined. Phylogenetic analysis of deep-sea isolates based on 16S rDNA sequences revealed that a wide range of taxa were represented. In contrast to bacteria, very few yeasts were isolated from such a great depth of 11000 m whereas various yeasts were isolated from the shallower sites from 1000 to 6500 m. The isolation frequency of yeasts fell as the depth of sampling site increased. The ratio of basidiomycetous yeasts to ascomycetous yeasts rose with increasing depth. Little diversity is observed among basidiomycetous isolates and Rhodotorulas occupied 89 % of all isolates. On the other hand, ascomycetous yeasts isolated at the shallower site than 2000 m showed a wide range of taxa such as Candida, Debaryomyces, Kluyveromyces, Pichia, Saccharomyces, and Willopsis. Some of isolates were identified as new species.
In studies aimed at further exploring the microbial diversity in various deep-sea environments, we have been attempting to isolate and characterize a number of bacteria from deep-sea mud collected by means of the manned submersibles Shinkai 2000 and 6500. Now, we are looking at the bacterial diversity and the occurrence of extremophilic bacteria at several deep-sea sites located near the south part of Japan.

2. Unique Enzyme from Deep-sea Isolate

We have isolated Pseudomonas-like amylase producer, the strain MS300, which displayed a large halo on starch medium, from the deepest site of Mariana trench. The strain MS300 produced two major and two miner a-maltotetraohydrolases (G4-amylase). The two major G4-amylases share the same molecular weight of 55,000 had different pI values of 5.0 and 4.7. The optimum temperature for activity of both major G4-amylases is 40°C and the optimum pH is 6.8 for one and 8.9 for the other. Under high hydrostatic pressure, the MS300 produced more amylase than under atmospheric pressure. Strain MS300 may be active in the deep sea at a depth of 10,897 m.



Effects of pressure on the grouth and amylase production by strain MS300. The cells were incubated at 4°C under various pressure conditions for 2 weeks. The number of colonyforming unit (CFU,open circle) was determined by counting the colonies that grew on Marine broth pletes after incubation. The cell density before incubation was 4.0 x 104 CFU/ml. Amylase activity (closed circle) was measured by the 2-dinitrosalitric reaction. Relative activity was calculated with maximum activity (0.1 MPa) taken as 100%.


Recent publications

  1. Hideto Takami, Akira Inoue, Fumie Fuji, Koki Horikoshi. (1997) Microbial Flora in the deepest sea mud of Mariana Trench. FEMS Microbiology Letters. 152 (2), 279-285

  2. Hideki Kobayashi, Yoshihiro Takaki, Kuniko Kobata, Hideto Takami, and Akira Inoue (1998) Characterization of alpha-maltotetraohydrolase produced by Pseudomonas sp. MS300 isolated from the deepest site of Mariana trench. Extremophiles. in press

  3. Hideki Kobayashi, Hideto Takami, Akira Inoue, and Koki Horikoshi (1998) Deep-Sea, new resource for screening of biocatalysis. Proceedings of an International Symposium held in Ede, The Netherlands. In : Studies in organic chemistry 53, New Frontiers in Screening for Microbial Biocatalysts (K. Kieslich, C.P. van der Beek. J.A.M. de Bont, and W.J.J. van den Tweel., Ed.) , pp. 259- 263. Elsevier.

  4. Hideto Takami, Takahiko Nagahama, Fumie Fuji, Akira Inoue, Fumiyoshi Abe, Koki Horikoshi (1998) Microbial Diversity in the Deep-sea Environment. American Geophysical Union, 1998 Spring Meeting S171

  5. Life at its lowest. SCIENCE NEWS 153 (24), June 13, 1998 (http:// www.sciencenews.org)