Nepal Journal of . Dec. 2015 Vol. 3, No. 1:68-70 ISSN 2091-1130 (Print) / ISSN 2467-9319 (online)

REVIEW ARTICLE Microbial Diversity in Freshwater and Marine Environment

Sagar Aryal1*, Gaurab Karki1, Sunil Pandey2 1Department of , St. Xavier’s College, Kathmandu, Nepal 2 Department of Microbiology, Nobel College, Kathmandu, Nepal Abstract covers seven tenths of the 's surface and occupies an estimated total volume of 1,386,000,000 cubic kilometers (km3). Of all the water found on Earth, 97% is marine. Maximum of this water is at a of 2 to 3°C and devoid of ; 62% is under high pressure (>100 atm). Microscopic phytoplankton and associated generate a complex web that can extend over long distances and extreme depths. The marine environment looks so vast that it will not be able to be exaggerated by pollution; however, in coastal areas activities are increasingly disrupting microbial processes and damaging .

Keywords: , , , Water, . *Corresponding Author Email: [email protected]

Introduction Prokaryotic are divided into two major Microbial diversity that we see today is the result of groups: the eubacteria, which include all bacteria of nearly 4 billion of evolutionary change. medical importance, and the archaebacteria, a Microbial diversity can be seen in many forms, collection of evolutionarily distinct organisms [1]. including size and cell , , Freshwater Microbial Diversity , pathogenicity, developmental , Freshwater and marine environments differ in many to environmental extremes, phylogeny and ways including , average temperature, depth, mechanism of [1]. and content, but both provide many excellent Microorganisms are present everywhere on Earth that for microorganisms. will support . These include habitats we are all Large numbers of microorganisms in a body of water familiar with- , water, , and -as well as generally indicate high nutrient levels in the water. virtually any made by . Some Water contaminated by inflows from systems microbial habitats are ones in which humans could not or from biodegradable industrial organic wastes is survive, being too hot or too cold, too acidic or too relatively high in bacterial numbers. Similarly, caustic, or too salty. Although such environments estuaries (fed by rivers) have higher nutrient levels would pose challenges to any life forms, they are often and therefore larger microbial populations than other teeming with microorganisms. Organisms inhabiting shoreline [8]. such extreme environments are called , a In water, particularly water with low nutrient remarkable group of microorganisms that collectively concentrations, microorganisms tend to grow on define the physiochemical limits to life [2]. stationary surfaces and on particulate . In this Approximately 6000 of and way, a has contact with more 100,000 species of have been formally than if it were randomly suspended and floating freely described [3]. In the case of the diversity of with the current. Many bacteria whose main is microorganisms, even the right order of magnitude is water often have appendages and holdfasts that attach unknown and the issue is highly controversial [4–6]. to various surfaces. The total number of prokaryotic cells in the has Freshwater environments are highly variable in the been estimated to be 1029 [7]. resources and conditions available for microbial All prokaryotic organisms are classified as bacteria, growth. Both oxygen producing and oxygen- whereas eukaryotic organisms include fungi, consuming organisms are present in aquatic , and helminths as well as humans. environments, and the balance between

©NJB, Biotechnology Society of Nepal 68 Nepjol.info/index.php/njb

Nepal Journal of Biotechnology. Dec. 2015 Vol. 3, No. 1:68-70 Aryal et al.

and respiration controls the natural meters at a constant 3°C temperature. The ocean, at its cycles of oxygen, carbon, and other nutrients greatest depth, is slightly more than 11,000 meters (nitrogen, phosphorus, metals). Among deep. The pressure in the marine environment microorganisms, oxygenic phototrophs include the increases approximately 1 atm/10 meters in depth, and . These can either be and pressures are in the vicinity of 1,000 atm at the planktonic (floating) and distributed throughout the greatest ocean depths [2]. water columns of lakes, sometimes accumulating in Much of the marine environment is covered by sea ice large numbers at a particular depth, or benthic, that may comprise up to 7% of the world’s surface. meaning they are attached to the bottom or sides of a Microorganisms actually grow and reproduce at the lake or stream. Because oxygenic phototrophs obtain interface between the ice and the seawater. The their from light and use water as an electron microbes that have been recovered from these ice donor to reduce CO to organic matter, they are called cores have been given intriguing generic names: these primary producers [9]. include Polaromonas, Marinobacter, Psychroflexus, A typical lake or pond serves as an example to Iceobacter, Polibacter, and Psychromonas antarcticus [2]. represent the various zones and the kinds of The world’s oceans are teeming with microscopic life found in a body of fresh water. The littoral forms. Nominal cell counts of >105 cells per ml in zone along the shore has considerable rooted surface sea water [12, 13] predict that the oceans vegetation, and light penetrates throughout it. The harbor 3.6 X 1029 microbial cells with a total cellular limnetic zone consists of the surface of the open water carbon content of 3 X 1017g [7]. Communities of area away from the shore. The profundal zone is the bacteria, , protists, and unicellular fungi deeper water under the limnetic zone. The benthic account for most of the oceanic . These zone contains the at the bottom [10]. microscopic factories are responsible for 98% of Areas of the limnetic zone with sufficient oxygen [7, 14] and mediate all contain pseudomonads and species of Cytophaga, biogeochemical cycles in the oceans [12]. Caulobacter, and Hyphomicrobium. Photosynthetic algae Coastal and shelf play a significant role in are located in the limnetic zone [11]. the remineralization of organic matter. In shelf areas, Deeper waters of the profundal and benthic zones an estimated 32 to 46% of the primary production have low oxygen concentrations and less light. Algal settles to the sea [15]. growth near the surface often filters the light, and it is Much of the primary in the open oceans, not unusual for photosynthetic microbes in deeper even at significant depths, comes from photosynthesis zones to use different wavelengths of light from those by prochlorophytes, tiny prokaryotic phototrophs that used by surface-layer photosynthesizers. Purple and are phylogenetically related to cyanobacteria. green sulfur bacteria are found in the profundal zone. Prochlorophytes contain chlorophylls a and b or These bacteria are anaerobic photosynthetic organisms chlorophylls a and d. The Prochlorococcus is a that metabolize H2S to sulfur and sulfate in the bottom particularly important primary producer in the marine sediments of the . Clostridium species are environment. Aerobic anoxygenic phototrophs include common in bottom sediments and may include bacteria such as Erythrobacter, , and organisms, particularly those causing Citromicrobium, all genera of Alphaproteobacteria. Deep- outbreaks of botulism in waterfowl [8]. water Archaea are almost exclusively species of , and many or perhaps even most are Marine Microbial Diversity -oxidizing chemolithotrophs, these The marine environment represents a major portion of organisms play an important role in coupling the the and contains 97% of the Earth’s water. marine carbon and nitrogen cycles. Very small Much of this is in the at a depth greater than planktonic heterotrophic bacteria inhabit pelagic 1,000 meters, representing 75% of the ocean’s volume. marine waters in numbers of 105 – 106 cells/ml. The The ocean has been called a “high-pressure most abundant of these is Pelagibacter, a genus of Class refrigerator,” with most of the volume below 100 Alphaproteobacteria. Cells of Pelagibacter are small

©NJB, Biotechnology Society of Nepal 69 Nepjol.info/index.php/njb

Nepal Journal of Biotechnology. Dec. 2015 Vol. 3, No. 1:68-70 Aryal et al.

rods that measure only 0.2– 0.5 µm, near the limits of 9. Tortora GJ, Funke BR, Case CL: Microbiology: An resolution of the light . Bacteroidetes and Introduction. 10th ed. 2010. San Francisco: Pearson Benjamin Cummings. Actinobacteria, and has also been found in 10. Rathi J: Microbial Physiology and Ecology. 1st nonhalophilic species of Archaea, such as the ed. 2009. Manglam Publishers & Distributors. Thermoplasma group. In the oceans, are more 11. Britannica.com: limnetic zone. ecology. Retrieved 2015- abundant than cellular microorganisms, often 08-14. From numbering over 107 virions/ml in typical seawater [1]. http://www.britannica.com/science/limnetic-zone 12. Porter KG and Feig YS: The use of DAPI for identifying Conclusion and counting aquatic microflora Limnol. Oceanogr.1980, Major bacterial groups now recognized as abundant in 25:943–948. 13. Hobbie JE, Daley RJ and Jasper S: Use of nuclepore the open ocean include Alpha- and filters for counting bacteria by fluorescence Gammaproteobacteria, cyanobacteria, Bacteroidetes, . Appl. Environ. Microbiol. 1977, 33:1225–1228. and to a lesser extent, Betaproteobacteria and 14. Atlas RM and Bartha R: : Actinobacteria; Firmicutes are only minor Fundamentals and Applications. 1993. components. With the exception of the cyanobacteria, (Benjamin/Cummings, Redwood City, CA). 15. Wollast, R: The coastal organic carbon cycle: uxes, most marine Bacteria are thought to be sources, and sinks. Ocean margin processes in global change adapted to extremely low nutrient availability, some 1991. pp. 365-381. augmenting energy conservation through proteorhodopsin or aerobic anoxygenic phototrophy. Recent anthropogenic interventions in marine environment have threatened all , including

microorganisms. Study of marine microbial

is of dynamic importance to the understanding of the different processes of the ocean, which may present effective novel microorganisms for screening of bioactive compounds.

References 1. Madigan MT, Martinko JM, Stahl DA, Clark DP: Brock th Biology of Microorganisms. 13 ed. 2012. San Francisco: Pearson Benjamin Cummings.

2. Prescott LM, Harley JP and Klein DA. Microbiology. 5th ed. 2002. The McGraw−Hill Companies. 3. Corliss JO, Margulis L, Melkonian M: Handbook of Protoctista 1st ed. 1990. Jones & Bartlett Publishers. 4. Finlay BJ and Esteban GF: Ubiquitous dispersal of free- living microorganisms. Microbial Diversity and 2004. ASM Press. pp. 216–224.

5. Hedlund BP and Staley JT: Microbial and . Microbial Diversity and Bioprospecting 2004 ASM Press. pp. 225–231. 6. Whitfield J: Biogeography: is everything everywhere? Science 2005. 310:960–961. 7. Whitman WB, Coleman DC and Wiebe WJ: Prokaryotes: the unseen majority. Proc. Natl. Acad. Sci 1998. 95:6578– 6583. 8. Tortoraand GJ, Funke BR: Microbiology: An Introduction. 9th ed. 2008. San Francisco: Pearson Benjamin Cummings.

©NJB, Biotechnology Society of Nepal 70 Nepjol.info/index.php/njb