mainly responsible for

The main person responsible for the school is Mary.

Joe(Anything else?)Nation

It could mean either, depending on context.

Mary is mainly responsible for the school, but she is also responsible for the church.

Mary is mainly responsible for the school, but John shares some of the work.

If I want to get rid of the ambiguity, does the following help:

Mainly Mary is responsible for the school. (I want to say that Mary is the main person in charge of the school).

Thank you both for the reply.

Why don't you say that, then? Or say Mary is head of the school, or that she is the principal?

I would simply say "Mary is in charge of the school". You don't have to wonder is she is responsible for it's creation, or if she caused it to burn to the ground.

Because I am using that sentence to represent a very long sentence full of technical terms, so I want to keep the sentence as simple and direct as possible.

@Roger: I can't use "in charge of." The sentence talks about the main bacterial strains responsible for the fermentation of X into Y.

Thank you. Oddly, I did not pick up on that or how technical the terms the terms were.

How does that preclude the use of "in charge of," exactly?

So I can say bacteria are in charge of something? I thought only people could be in charge of things.

I have just searched "bacteria in charge of" in the gov, edu and uk domains and not a single instance was found.

Try this:
Give us the actual context of the sentence you are trying to write. The confusion is arising out of your use of "Mary" (a person) to write about what we now know is a bacterium. (not a person)

Give us the context, we'll have another go at it.
Joe(Plainly mainly lamely doesn't do it)Nation

Here you go:

Although the classification of acetic bacteria is very problematic, it is estimated that mainly 20 strains of the species A, B, C, D, E and F are responsible for submerged acetification in the food industry.

Why can't you leave it as it is?

If it is good now it will stay as it is. I was not sure about where to insert the adverb "mainly." I was afraid that if I put it before "responsible," that the sentence would state that the main use of those strains is submerged acetification, which is not the intended meaning. I only realized I could put the adverb before "2o strains" when I wrote the simpler version of the sentence (Mary is responsible for the school).

It is an inept surrogate.

1) Although the classification of acetic bacteria is very problematic, it is estimated that twenty strains of the species A, B, C, D, E and F are mainly responsible for submerged acetification in the food industry.

You might need more data. Are the twenty strains of A,B,C,D,F a minority of the total strains??

2) Although the classification of acetic bacteria is very problematic, it is estimated that just twenty of the __X____strains of the species A, B, C, D, E and F are mainly responsible for submerged acetification in the food industry.

3) Although the classification of acetic bacteria is very problematic, it is estimated that twenty strains of the species A, B, C, D, E and F are primarily responsible for submerged acetification in the food industry.

I never use numbers (1,2,3...20) when a word (one, two, three, ...twenty) is available. I think I was either taught that or decided it on my own.

Do you see the difference between examples one and two?

I think 'primarily' is a better word here than 'mainly'.

Joe(My Most Humble Opinion)Nation

The letter O and the figure 0 (zero) are not interchangeable. A lower case letter o is especially wrong.

Thanks very much, Joe. Number 3 is perfect, "3) Although the classification of acetic bacteria is very problematic, it is estimated that twenty strains of the species A, B, C, D, E and F are primarily responsible for submerged acetification in the food industry."

Contrex, that is supposed to be a zero, not an "o" or "O." I copied/pasted from MS Word.