There is only a short time of the year when you can see the sun coming down into the canyon, and then only at midday. Tours at that time of the day and that time of the year sell out far in advance. You may need to book at least six months ahead of time, for a summer month tour, to take advantage of this.
The crystal violet and bile salts inhibit the growth of gram-positive organisms which allows for the selection and isolation of gram-negative bacteria. Enteric bacteria that have the ability to ferment lactose can be detected using the carbohydrate lactose, and the pH indicator neutral red.
Glucose is the prototype food source: all fermentative bacteria will use glucose. Sucrose & lactose are disaccharides, must be cleaved into monosaccharides. Not all bacteria, and not all fermenters, can do this, so glucose fermenters may or may not ferment sucrose/lactose. Obligate aerobes cannot ferment. (they