Troubleshooting no transformants

No colonies on the antibiotic plate is a pattern with several causes, and the decision is which cause the controls have left standing. This troubleshooting page stays with non-pathogenic E. coli cloning strains. The transformation it assumes is the one in bacterial culture and transformation. The DNA that should have become a circle is plasmid cloning from insert to colony. The drug on the empty plate is meaningful only if it matches the marker, as antibiotic selection and blue-white screening explains.

Cells, plates and recovery media are specified from the reagents and chemicals catalogue. Method context is the molecular biology pathway. If the insert itself may be the problem, frame that with the custom gene synthesis reference. The practical specification goes to the quote request. A method can be discussed. A public order of operations is the Addgene bacterial transformation protocol.

Read the pattern, not the disappointment

An empty plate does not say "the cloning failed" in one voice. It says no colony was visible under the conditions you set. Those conditions include the cells, the pulse or the heat shock, the recovery, the DNA, the antibiotic, the wetness of the agar, and the incubator. Change them one at a time, and only after a control has pointed. Replacing the ligase, the cells and the plates in one afternoon produces a success you cannot explain or a second failure you cannot assign.

Keep the no-DNA plate in the set. If it grows, you do not have "no transformants". You have a plate that cannot tell transformants from anyone else. Fix selection before you troubleshoot uptake.

The branches that actually produce a blank

Cells that were never competent, or that warmed on the bench, will not take up DNA. A known plasmid fails with them. That branch is the cells.

The wrong antibiotic, or the right antibiotic destroyed by heat when the plates were poured, usually does the opposite and gives a lawn. The exception is a drug that is still active and is not the drug your marker resists: a bla plasmid on a genuine kanamycin plate gives a true blank. Read the bottle, not your memory of the sleeve.

Plates poured and used while the agar is still hot enough to kill cells give a blank that looks like bad DNA. The known plasmid dies too. Cool plates to incubation temperature before you spread.

DNA that is the wrong plasmid, linear DNA that cannot replicate, or a ligation that never circularised gives a blank only on the experimental plate. The known plasmid grows. Salt in a ligation is a special case of bad DNA for electroporation: the pulse arcs or silently fails, while a chemical transformation of a smaller volume might still have worked. Match the cleanup to the competence type.

Heat shock mistimed, either skipped when the sheet required it or extended far past the printed seconds, kills this branch of the method. Electroporation has its own version: a warm cuvette, a bubble, salt. Recovery skipped sits on both branches. The marker gene cannot protect a cell that has not yet made the protein.

Plates dried until the surface is cracked give no colonies because the cells never formed them, not because DNA failed to enter. A trusted plasmid on a fresh plate from a different sleeve distinguishes dried agar from dead cells. An incubator set far from the strain's temperature, or read too early at a temperature where this plasmid grows slowly, is the last branch. Look again later, or set the temperature you meant, before you throw out the reaction.

A control plasmid this lot has already accepted

Use a small amount of intact plasmid that has made colonies in this strain before. Keep it in water if you might electroporate it. Plate it on the same day, on the same batch of plates, with the same recovery. ATCC culture guides talk about checking material you receive. A control plasmid is that instinct applied to a Tuesday afternoon.

Interpret only the pair. Control grows, experiment empty, no-DNA empty: DNA or assembly. Control empty, experiment empty, no-DNA empty: cells, pulse, recovery, plates, incubator, or the drug is hostile. Control empty, experiment empty, a plain non-selective plate shows a lawn: the cells were alive and something about selection or the method killed only the would-be transformants, or the selective plates are toxic. No-DNA grows: stop, the blank experiment is not interpretable. Control grows and the experiment is a lawn: you may have plated far too much of a successful reaction, or that one plate lacked drug. Those are not "no transformants". They are the neighbouring patterns, included so you do not force them into this tree.

Four outcomes worth drawing

Do not add a fifth story too early

Contamination, a toxic gene that kills every cell that takes it up, and a promoter that expresses something lethal even before you induce, can also empty a plate. They are later stories. A toxic construct still allows the control plasmid to grow. If the control is empty, toxicity of the new gene is not your explanation. If the control grows and a gentler backbone with the same insert also dies, toxicity earns a look. Lower the incubation temperature only as a deliberate test, and say so in the notebook.

Wrong incubator temperature is more ordinary than a toxic gene. A room labelled 37 that is actually much hotter can kill a recovery. A cold room used by mistake will look empty in the morning and populated, or still empty, a day later. Read the plates at the time the strain needs, not at the time you hoped.

Promega protocols show how supplier sheets separate cell controls from DNA controls. Follow that separation even when you are impatient.

Scope and safety

This tree is for cloning strains already accepted on your bench. It is not a way to diagnose a failed culture of a pathogen, and it does not tell you how to grow one. If the organism is outside the institutional list, stop and take the risk assessment to the people who own it. Do not troubleshoot an unapproved bacterium by varying rich media until something grows. The WHO Laboratory Biosafety Manual is a reference for that institutional decision. This page is not medical advice. Inactivate the recovery cultures you do not plate.

Hot pours, dishonest incubators, dried agar

In a hot laboratory, agar that "feels cool enough" can still be warm enough to damage a heat-labile drug or to stress cells spread too soon. Use the cooling time your method already trusts, and keep a thermometer for the incubator rather than trusting a faded sticker. A fan-forced incubator in a dry week will crust plates left unbagged. Those plates look like a transformation failure of everything you try. One fresh plate with the control plasmid ends the argument. A power cut during recovery is a reason to discard that recovery, not to plate it the next day and interpret the blank as a genetic result.

What to send when you ask

State the strain, chemical competence or electroporation, the marker, the control-plasmid result, whether recovery happened, the age and dryness of the plates, and the incubator temperature you measured. Ask for the cell specification that matches that pattern. Put it on the quote request. A method can be discussed. The custom gene synthesis reference is appropriate when the control says the cells are fine and the new sequence is the remaining suspect. It does not mean a gene is already being synthesised.