A Microbial Biorealm page on the genus Hnk001
Higher order taxa
Bacteria; Proteobacteria; Gammaproteobacteria; Alteromonadales; Psychromonadaceae; Psychromonas[Others may be used. Use NCBI link to find]
Description and significance
In May, 1991 P. ingrahamii was isolated from Elson Lagoon in Point Barrow, Alaska ice-water interface. Psychromonas ingrahamii was named after John L. Ingraham, a microbiologist devoted to research on psychrophilic bacteria. Psychrophilic means “cold-loving” and psychrophilic bacteria shows maximal growth at 20 celcius, 15 celcius or lower for optimal growth and 0 celcius or lower for minimum growth. (Richard Y. Morita) To study in detail, it was monitored for steady growth in the Ordal’s sea water cytophaga medium (SWCm). The Colonies grown on plates were circular, white and smooth. (Ann J. Auman, Jennifer L. Breezee, John J. Gosink,…) Phase contrast and transmission electron micrographs of cells revealed various features of organism including cell size, shape and structure. P. ingrahamii is a Gram-negative bacterium, rod-shaped and non-motile. It is also facultatively aerobic indicating its ability for both respiratory and fermentative metabolism. They are about 6-14 um long and grows in a moderate salt concentraton environment-lack of salt resulted in no growth where as high concentration of salt showed weak growth rate. P. ingrahamii lives in neutral water with optimal pH range from 6.5 to 7.4. P. ingrahamii reduces inorganic nitrate and is a heterotroph utilizing many organic compounds for carbon sources. However, interestingly, it does not hydrolyse starch or gelatin and seems to have no flagellas unlike other organisms in its family. Also P. ingrahamii is found to grow at subfreezing temperature (lowest growth temperature of any organism studied so far) -12 celcius with 240 h generation time. On the other hand, the organism shows a 12 hours generation time at 5 celceus, its optimum temperature. Cells were placed in singles, pairs or in a short chain. (Ann J. Auman, Jennifer L. Breezee, John J. Gosink,…) Under electron microscopy two different shapes of gas vacuoles were found, which is unusual and only seen in Halobacterium halobium-halophilic archaeon; different type of prokaryotic microorganism from bacteria which lives in an environment with high salt concentration. (Richard Y. Morita). The study of p. ingrahamii is significant because it could spur the interest to discover and assess the diversity of psychrophilic organisms and to learn how they can sustain and grow at low temperatures. Also, study of psychrophiles may provide possibility that other planets support such life as well at subfreezing temperatures. (J breeze, N. Cady and J.T. Staley)
DNA purification reagent-hexadecyltrimethylammonium bromide miniprep protocol-was used to collect DNA to study base composition and the HPLC (high performance liquid chromatography), a type of column chromatography, is used to study the DNA. P. ingrahamii has genome size approximately 4.5 Mb. Among the four different bases, the base pair that forms three hydrogen bonds G+C content was 40 mol%. Other members in its genus psychromonas have the range from 38.1 to 43.8 mol%. (Ann J.) 16S rRNA gene of P. ingrahamii was amplified by PCR (polymerase chain reaction) and was sequenced. The sequence was inserted into the National Center for Biotechnology Information (NCBI) web site (ncbi.nlm.nih.gov). One of the five organisms with high similarity sequences was Psychromonas antarcticus with 96.8% sequence similarity. (Ann J. and Breeze). Although p. antarcticus was found to be the most closely related known species of p. ingrahamii based on DNA sequence, interestingly they exhibit significant different phenotypic features. P. antarcticus is relatively small, motile and does not have vesicles. For further comparison, the sequences of E. coli and organisms from other groups within the Proteobacteria were aligned with p. ingrahamii to draw a tree arrangement. (breeze)
Cell structure and metabolism
P. ingrahamii are large rod-shaped, arranged in singles or pairs sometimes in a short chain. Its length is about 6 to 14 um, relatively large compared to the rest of the speceies within the same group. P. ingrahamii is the only species producing gas vesicles, non-motile, and able to hydrolyse polymers of neither starch nor gelatin unlike other members of Psychromonas. Two different shapes of gas vacuoles were found in the organism. One was large in number, short, wide cylinders with conical tips and the other was seen rarely with longer length but narrow width with conical tips too. Within the gas vacuoles, there are small, rigid, protein-like subunit vesicles. These are permeable to gas and minimize the cell’s density and therefore, provide the buoyancy. However, the exact function of these gas vacuoles in polar sea ice environment particularly is not known yet. (Ann J. Auman) When cultured in the media, the colonies looked white, smooth and convex. P. ingrahamii can utilize a variety of carbon sources including D-galactose, D-mannitol, N-acetylglucosamine, cellobiose, sucrose, fumarate, DL-lactate, glycerol. Carbon sources fermented are D-glucose (gas), lactose, and Trehalose (Ann J. Auman) The fact that p. ingrahamii can grow and reproduce even at slow rate, 10 days generation time, indicates possibly different physiological, metabolic activities from that at high temperatures. At low temperatures, protein denaturation is not likely to occus but instead, for the psychrophiles, the membrane transport and fluidity are the main concerns. The analysis of fatty acid composition was showed the main composition of 16-carbon unsaturated (67%) and saturated fatty acids (18.7%). The fatty acids composition and cold-adapted enzymes in psychrophilic bacteria are extensively studied currently.
When liquid water contains salt, its freezing point drops below 0 celceus. Organisms live in liquid water at subzero temperatures. Sea Ice microbial community (SIMCO) is a specific example inhabited by diatoms, protests and bacteria. The SIMCO consists ~10% of the ocean surface. The sea ice in SIMCO environment ranges from -1.8 celceus to -30 celcius or lower according the local surface temperature. (J breeze, N. Cady and J.T. Staley) According to different season, the availability and salinity of the temperature, light and nutrient change in the sea ice environment. Approximately 10 to 20cm below the sea ice column from the ice-water interface, SIMCOs are prevalent where the nutrients from the water and surface light exist and where there’s high chlorophyll a content. Recently, it was reported that the SIMCOs exhibit a great diversity of bacteria. Even though p. ingrahamii is the only species within the psychromonas genus, there are many bacteria with gas vacuoles and they are phylogenetically diverse. In polar habitats, activities of numerous algae are accountable for the primary production. Algae also dominates the SIMCOs population and heterotrophic bacteria are the secondary producers. (John J. gosink) In 1980, Sullivan and Palmisano from University of Southern California found diver bacterial community in McMurdo Sound, Antarctica and included various pictures of many different types of bacteria living in the sea ice.
Studies have not been able to identify Psychromonas ingrahamii as a pathogen, causing any disease.
Application to Biotechnology
Psychrophilic organisms are interesting and noteworthy in the field of biotechnology because of their different physiology from other organisms. They must have adapted special mechanisms and metabolism to thrive in such lower temperature environments. Many psychrophilic organisms including p. ingrahamii contain cold-adapted enzymes that are being studied with great interest. Since they must regulate their membrane fulidy and transport, some microbiologist have been studying psychrophilic organisms enzymes to find more about how life is sustained at low temperature and furthermore, these enzymes may be considered in products and industries such as food processing (fermentation, bakery), cleaning agents, degradation of xenobiotic compounds in cold climate. In addition, according to the recent research, protein folding is responsible for forming the ability to live in cold environments. Further discovery of metabolism and mechanisms of psychrophilic organisms’ cold adaptation would lead to our great advantage to understand protein function and structure better. One of the Earth’s pristine environements is Antarctica. There have been a few spills of fuel over the past and this spurred and initiated study to find out the ability of Antarctic microorganisms to degrade hydrocarbon. Surprisingly, some Antarctic bacteria were found to degrade many hydrocarbons of fuel spills from experiment done in Eastern Antarctica. (David Nichols, John bowman) However, despite these great advantages and findings applicable to biotechnology, some difficulties reside in studying psychrophilic organisms particularly including p. ingrahamii. It is crucial to maintain the conditions in the growth medium to provide the environment for the psychrophilic organisms to grow. Thus consistant low-temeprature conditions should be maintained throughout the growth experiments for many weeks.
Enter summaries of the most recent research here--at least three required
[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.
Edited by student Hana Kim of Rachel Larsen and Kit Pogliano