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Sea water under the microscope

Associate Professor Justin Seymour introduced AQOB to the jungles to be found in just a drop of sea water and the complex web of life of Earth's most numerous creatures - single celled bacteria and relatives. These so called simple organisms are descendants of the earliest forms of life on Earth and have continued to thrive in vastly different environments from those that existed when they first evolved. They are outstandingly successful life forms that are invisible to the naked eye and so in general their vast numbers and essential roles for human survival are not recognised. This page and interview were opened in 2010. The main change is Dr Seymour is now an Associate Professor and continues to elucidate the roles of marine microorganisms with enthusiasm.   Editor December 2016 

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Dr Justin Seymour studies marine micro-organisms which can only be seen through a microscope. He works in The Plant Functional Biology and Climate Change Cluster at the University of Technology Sydney and studies an invisible underwater environment that acts very much like the jungles on dry land    
As a teenager, Justin’s interest in surfing and science set him wondering why he often became sick (conjunctivitis, ear infections) after surfing, especially in winter and especially after storms. This led to his study of micro-organisms for his Honour’s degree. Now, his post Doctoral research focuses on the behaviour and movement of bacteria in the ocean from a small scale view.

Ocean bacteria have a very different life to most of those we know of, and which make people sick. They live in a nutrient depleted environment and so have to take advantage of nutrients whenever they can.     
Plankton, moving through the water, for instance, leave a trail of excretion behind, which the bacteria can use as a nutrient source. They swim using flagella, which are small tail-like structures. To find food sources the bacteria use chemotaxis, which is the ability of bacteria to swim and change direction in relation to chemical stimuli. This is triggered by sensors on the outside of the cell which measure the concentrations of different chemicals. Each bacterium is only a micron in size and travels distances of less than millimetres. This sounds like a very small distance, but from a bacteria perspective it is the equivalent of a zebra roaming distances across a plain for a water source, even though the bacteria are roaming within a single drop of water.
While plankton waste is a source of nutrients for bacteria, the main source comes from algae or phytoplankton, which are the plants or trees of the ocean. When they photosynthesise they release carbon compounds back into the water column, which the bacteria feed on, and eventually recycle back into the food web.

Below: swimming tracks of the marine bacteria Pseudoalteromonas haloplanktis clustering in a patch of nutrients.

One particular compound, an organic sulphur compound called Dimethylsulfoniopropionate is especially relevant, as it is a precursor to dimethylsulphide (DMS), which is a major source of sulpur aerosols from the ocean into the atmosphere, which is an important element in cloud formation. Changes in oceanic bacterial communities can affect the release of DMS and could ultimately affect rainfall.

There are instances where the bacteria and the phytoplankton have a cooperative arrangement. While the algae release carbon rich substrates which is essential for bacterial growth, the bacteria release nitrogen and phosphorous which benefits algal growth. Such a close relationship is not affected by turbulence because the world of bacteria are so small that turbulence has no effect.
The samples Justin studies come from regions as diverse as Antarctica and The Great Barrier Reef.
(Below, Justin working in Antarctica)

For example those from Antarctica have been used to look into how large scale oceanographic features might influence the community structure of bacteria. Research into the associations between bacteria, viruses and the surfaces of corals reefs has shown that there is spatial interaction between viruses and corals, so it is now a matter of knowing whether the viruses affect coral health.

It’s a crowded world under the microscope. Each drop of seawater water contains around a million bacteria and ten million viruses, along with other players in the microbial food web, which includes predators that eat the bacteria. In effect this is the bottom of the food web and the efficiency of the processes within it can ultimately affect larger food webs,such as those in fisheries. In the ocean 95% of the biomass is made up of these micro-organisms and bacteria can withstand water temperatures from 0° to over 80° in deep water thermal vents at the bottom of oceans. It is incredible that humans remain largely untouched by this mass of bacteria, although some are known to infect wounds and one, vibrio cholera, can cause cholera, particularly in third world regions.

The mini world of bacteria and algae is also important to the carbon cycle and one predicted effect of global warming is an increased stratification of oceans. The increase in the temperature gradient from the surface layer to the depths where the nutrients are may create an enhanced density boundary layer, resulting in fewer nutrients rising to the surface and becoming available for the phytoplankton. In turn this would lessen their growth and draw down less less carbon dioxide from the atmosphere via their photosynthesis.

It is extraordinary to discover the wide-ranging effects these micro-organisms can have

Images from Justin Seymour
Text: V.B. May 2010.

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