Hasanul Banna Siam ,
Minhajul Abedin ,
Sakibur Rahat, and
Belayet Hasan Limon
[ Special thanks to our course Teacher Samina Madam for her encouragement and support]
[Also thanks to Nayeema Ema, Afroza Khan, and Raihan Reza for helping us in serial dilution and inoculation]
If you look at the map, you can find an astonishing pattern. Almost every big city in the world was founded either by the side of a sea or a river because it provided the advantages of commerce and sustainability. The city of Dhaka is no exception in this case. Dhaka city was founded about four hundred years ago by the side of the river Buriganga, and it was the lifeline of the city.
During the time of Mughals (1600CE), the banks of the Buriganga served as a prime location for trade and also the city’s main source of water.
However, this is not the case anymore. Today, the Buriganga River is afflicted by the chemical waste of mills, factories, household waste, medical waste, sewage, dead animals, plastics, and oil etc. The city of Dhaka discharges about 4,500 tons of solid waste every day and most of it is released into the Buriganga. Water pollution in the River Buriganga is at its highest ever. The most significant source of pollution appears to be from tanneries in the Hazaribagh area.
About 4,500 tons of solid waste being discharged in Buriganga every day
All these frightful information give us an insight of how aquatic life is being severely hampered in this river. For fishes to survive, the river water must maintain >5 ppm Dissolved Oxygen (DO) level. Yet, the DO level becomes very low (<0.78ppm) and almost non-existent during dry season making the river very toxic.
Fishes can hardly survive in this stressful condition, but what about Bacteria?
As microbiology undergrad students, playing with Bacteria has always been a fun thing to us. So we asked ourselves a few questions:
- Can Bacteria survive in Buriganga River water?
- If yes, then do they have diversity? Or, a single evolutionary successful species is ruling the whole area?
To find the answer to our questions, we approached our Environmental Microbiology Course Teacher. She helped us a lot in providing a step-by-step guideline and managing us a Sterilized Jar to collect Water.
[Sterilized jars are free from any kind of living organisms. In order to avoid contamination, the jars must be sterilized before collecting sample]
We managed to collect our sample from the middle part of the river with a boat from Showari Ghat area in the afternoon with the temperature being more or less 30 Degree Celsius. We couldn’t record the pH of the water since we didn’t have the pH meter. In any case, we carefully did collect sample water and preserved it for the next day’s experiment.
In the Lab, we were provided with four Nutrient-Agar-Media, two m-FC (membrane fecal coliform) media and four test tubes.
[ Nutrient-Agar-Medium = Think of it like a small dish in which we put foods for Bacteria so that it can show visible growth within 24 hours ]
[ m-FC is the same as NA Medium, but it is specially designed to show growth of a particular type of Bacteria (i.e. bacteria coming from fecal origin) ]
We began our work by doing serial-dilution. It is done to decrease the number of organisms and to get the proper result within a small petri-dish. The test tubes were marked as 10^(-1), 10^(-2), 10^(-3) and 10^(-4) respectively.
We inoculated the sample on the four Nutrient-Agar-Media using Streak and Spread plate method.
- Original/Stock [Streak]
- 10^(-1) [Spread]
- 10^(-3) [The diluted 10^(-2) sample was not used]
- 10^(-4) [spread]
The remaining two m-FC plates were marked and performed on spread plate method:
1. 10^(-1), lowest dilution
2. 10^(-4), highest dilution
After the inoculation, the plates were placed inside separate refrigerators at 37⁰C for N.A., and 44.5⁰C for mFC media for proper growth.
We found the answer to our first question.
Yes, Bacteria can grow under this severely disturbed environment of Buriganga River, but the type of bacteria that are growing in this water may not be a good news for us.
This Picture shows the growth of bacteria coming from Fecal Origin. The presence of fecal coliform indicates that the water has been contaminated with the fecal material of humans or other animals.
Large quantities of fecal coliform bacteria may indicate the presence of pathogens in the water. Some waterborne pathogenic diseases that may coincide with fecal coliform contamination include ear infections, dysentery, typhoid fever, viral and bacterial gastroenteritis, and hepatitis A.
Untreated fecal material that contains fecal coliform can be harmful to the environment. Since it adds excess organic material to the water, the decay of this material depletes the dissolved oxygen level. This lowered oxygen level can potentially exterminate the existence of fish and other aquatic life.
The second picture provides a quite interesting information that, when diluted 4 times, only one single colony of fecal coliform was found.
This means, Buriganga River has Fecal Coliform bacteria, but not in tremendous amount. We can still hope to treat its water will the minimal level of Chlorine and disinfectant chemicals.
Let us now look at the Nutrient Agar Plates to check if there is microbial diversity in our sample water.
The above picture reveals a huge amount of growth within 24 hours dominated by different kinds of species.
Various types of colonies are seen after one fold dilution.
This Plate is suitable for analyzing different colonies. If we focus at the white circles, we can see that not all of them are same. Different types of bacteria produce different-looking colonies, some colonies may be colored, some are circular in shape, and some are irregular. This means diversity.
[Plate Interpretation: Colony Morphology, http://www.sciencebuddies.org/science-fair-projects/project_ideas/MicroBio_Interpreting_Plates.shtml ]
How did bacteria manage to grow in such stressed condition?!
Bacteria are a prokaryotic and very primitive life form that has survived and dominated this planet earth alone for 2.8 billion years. Many of them can live without oxygen, resist pH change, live in temperature above 100C, withstand high radiation, degrade the toxic material and so on.
Low level of dissolved oxygen in Buriganga may be a problem for aerobic bacteria, but not for anaerobes. Anaerobic bacteria such as fecal coliform use other molecules instead of oxygen as their final electron acceptor in ‘Electron Transport Chain’ to produce energy.
Since Bacteria have faster growth rate, they are evolutionary more adaptive to the changes in the environment.
Buriganga River has lost its glory. Once upon a time, it had clean water to drink and clean air to breathe, but now — river banks are filled up with piles of wastes, and the bad odor coming out of the water is just too nasty.
It is heartbreaking to think how our Govt. and we have left taking care of this river that once gave us so much. In fact, up to this day, it is a major route for water transportation in our country.
The Good News is, Life still survives here and diversity thrives. We still have hope.
If we can take proper action immediately, we may very well save this river and bring back its beauty just like the Thames River of London. We hope that the concerned ones realize and take heed soon.