My undergraduate thesis project - Lactose metabolism

[victor]

Hi, my name is Victor and I'm about to start my research project for an undergraduate thesis.
The research theme is to elucidate biochemical pathway of lactose utilization by bacteria from Sermo dam isolate. The background which made me decide to start a research about it is when I test this strain's physiological characteristics in fermenting carbohydrates. I used glucose and lactose broth and phenol red as the pH indicator. What happen to those medium were that in glucose medium, the bacteria started fermenting it and after 48h it produced acid and gas (the medium turns yellow). But when it's incubated in lactose medium, after 48h the medium was still red (no pH change) and the bacteria grew there.

Then I think that lactose in bacteria is cleaved into glucose and galactose by beta-galactosidase, where galactose is converted into glucose either via Leloir pathway like in E.coli or tagatose pathway like in lactobacilli. So, if the end product of lactose cleavage is glucose, then why doesn't the bacteria ferment it like what E.coli does (because I also compared it with E.coli)?

My hypothesis is that the beta-galactosidase enzyme in this bacteria has a low catalytic rate (or low affinity) towards lactose, causing the glucose as the end product does not get accumulated so quickly. With this phenomenon, it enables the NAD+/NADH recycle undisturbed, so all the glucose would be completely oxidized into CO2 instead of cleaved into pyruvates and reduced to alcohol/lactate.

So the main research that I conduct is measuring the activity of beta-galactosidase in this bacteria and compare it with E.coli.

So, I wanna ask the opinion of all the people in this forum and also suggestions if necessary. Thanks for the attention.

Regrads,
Victor Apriel

[MrMistery]

So how are you going to do it?

[victor]

First of all, I want to do an identification towards this bacteria until the genus, because at least I have to know which phylum that this bacteria belong to. After that I want to do an beta-galactosidase enzyme assay for this bacteria and compare it with the same assay on E.coli strain K12.

Any suggestion or addition about this? anything would be appreciated.

Thanks
Victor