On this page
Most of the life you study runs on sunlight: plants capture it, and animals eat the plants. Sergei Winogradsky found bacteria that do without it, living instead on energy released by oxidising chemicals such as hydrogen sulfide and ammonia. This post covers how he showed it, balances the reactions involved, and links them to your NCERT syllabus.
Who was Sergei Winogradsky?
A review in FEMS Microbiology Reviews by Martin Dworkin and David Gutnick calls him a founder of modern microbiology and the first microbial ecologist. Their abstract gives the outline of his life. He was born in Russia in 1856 and studied the yeast Mycoderma vini for his master's degree at the University of St Petersburg. He then joined the laboratory of Anton de Bary in Strassburg, and later moved to the Swiss Polytechnic Institute in Zurich.
He returned to Russia, retired from science for 15 years on his family estate in Ukraine, and was forced to flee after the Russian revolution. He spent his last 24 years at the Pasteur Institute in Paris, building the field of microbial ecology, and died in 1953.
What did Beggiatoa teach him?
In Strassburg he studied Beggiatoa, a bacterium that oxidises sulfur compounds. According to Dworkin and Gutnick, this work led him to formulate the theory of chemolithotrophy: some organisms get their energy by oxidising inorganic substances. An entry by Aharon Oren in the Encyclopedia of Life Sciences says his work on nitrification and the colourless sulfur bacteria led to his discovery of the chemolithotrophic mode of life.
G. A. Zavarzin's 2006 article Winogradsky and modern microbiology lists the discovery of chemosynthesis among his main contributions, along with the elective method: setting up growth conditions that favour the kind of microbe you want to study.
How did he explain nitrification?
In Zurich he turned to soil nitrogen. Dworkin and Gutnick write that he isolated the first pure cultures of nitrifying bacteria and confirmed that these bacteria carry out two separate steps: ammonia to nitrite, and nitrite to nitrate. That work led directly to the idea of the nitrogen and sulfur cycles in nature. Back in Russia he was also the first to isolate a free-living bacterium that fixes nitrogen gas.
Worked example: balancing the reactions
Use oxidation states to see where the energy comes from. Each step strips electrons from nitrogen or sulfur.
Step 1: ammonium to nitrite. Nitrogen goes from -3 in NH4+ to +3 in NO2-, a loss of 6 electrons per nitrogen.
2NH4+ + 3O2 → 2NO2- + 4H+ + 2H2O
Check the balance. Left: N 2, H 8, O 6, charge +2. Right: N 2, H 4 + 4 = 8, O 4 + 2 = 6, charge -2 + 4 = +2. Balanced.
Step 2: nitrite to nitrate. Nitrogen goes from +3 to +5, a loss of 2 electrons.
2NO2- + O2 → 2NO3-
Left: N 2, O 6, charge -2. Right: N 2, O 6, charge -2. Balanced.
Sulfur, as in Beggiatoa. Sulfur goes from -2 in H2S to 0 in elemental sulfur.
2H2S + O2 → 2S + 2H2O
Left: H 4, S 2, O 2. Right: S 2, H 4, O 2. Balanced.
Common mistakes to avoid:
Getting the oxidation state of N in NH4+ wrong. Hydrogen is +1, so 4(+1) + N = +1 gives N = -3.
Thinking nitrate can be oxidised further. +5 is the highest oxidation state of nitrogen, so nitrate is the end of the line.
Calling chemosynthesis "photosynthesis in the dark". It uses a different energy source: chemical oxidation, not light.
What does NCERT say?
The current NCERT Class 11 Biology chapter 2, Biological Classification (2026-27 reprint), says some bacteria are autotrophic, making their own food from inorganic substrates, either by photosynthesis or by chemosynthesis. It describes chemosynthetic autotrophic bacteria as oxidising inorganic substances such as nitrates, nitrites and ammonia, using the released energy for ATP production, and playing a large role in recycling nitrogen, phosphorus, iron and sulfur.
For how other microbes help in sewage treatment, biogas and medicines, see our guide to microbes in human welfare.
What is a Winogradsky column?
A 2024 paper in the Journal of Microbiology and Biology Education notes that Winogradsky columns were invented by Winogradsky in the 1880s and are widely used in school and college teaching. A traditional column is a container of soil or sediment from nature with added nutrients. The paper describes the columns as model ecosystems in which students can watch microbial communities develop and interact.
What can a student learn from how Winogradsky worked?
Study things in conditions close to nature. His elective method let each microbe show what it does best.
Separate a process into steps. Nitrification became two distinct reactions, each studied on its own.
Connect small to large. A single culture led to the idea of element cycles across the planet.
When you want to check an oxidation-state calculation or a balanced equation, the Fermi Problem Library has worked problems with a step-by-step solver that explains the reasoning rather than printing an answer. For the scientist who later redrew the tree of microbial life, read about Carl Woese and the archaea.
Write the two nitrification equations from memory, then mark the oxidation state of nitrogen above each species.
