Thanks for taking the time to read and comment!
I would say that most scientists hold the belief that TRUTH will most of the time be beneficial to us, so investigating genes or whatever will ultimately help us. We are basically learning to control nature, in order to realize our values (or satisfy our desires, to put it more plainly).
Now, philosophy has already challenged the idea that truth is always good/useful for you.
Philosophy has also challenged the idea that science searches for truth regardless of desires etc. This is easy to see: there are many truths/facts out there, but we concentrate on very few of them. For example, right now there is an answer to the question "how many worms are there in my garden?" There is also an answer to the question "how many cigarette butts are there in the street where I live". But I don't go out to investigate these issues. Why? Because I don't see the use. If science really cared about all truths equally, you would find scientists doing crazy stuff all the time, like counting the leaves that fell on the ground under a tree, or counting how many times you have blinked in the last minute. These are all facts, after all! So the plain statement that is often given, "science is interested in the facts" is not exactly true: science is not equally interested in ALL facts!
So your question about what drives these scientists to do their work is valid. But the answer I think won't be too different to what drives anyone to do any kind of work. Scientists are not that different from other human beings.
I, personally, would indeed like to live indefinitely! But so does everyone: why did we invent the afterlife in almost all cultures we know about?
There's many things I could say about all this, but I will end by saying that there is indeed an element of "faith" here, the faith that knowing the truth will improve human lives, and relationships.
Btw I studied philosophy, not science, and am currently writing a novel! But I'm like a Renaissance man, I'm interested in all the sciences (though mostly biology, among the hard sciences) and all social and soft sciences, and art, and generally life is very hard for me because I find everything fascinating but not enough time to study everything! :P