Question

Microbiology

a) For each of the following parameters, indicate a method/approach that could be used to estimate it.

- Bacterial activity in the water of a lake

- The fraction of bacteria that are metabolically active in the water of a lake

- The number of cells of a particular phylogenetic group of microorganisms, e.g. methanogens

b) Design enrichment cultures for the following types of bacteria. Recall the Winogradsky column

Organisms	Energy source	Carbon source	Terminal electron acceptor	Incubation conditions (anoxic/oxic, light, etc.)
Cyanobacteria
Purple sulfur bacteria
Denitrifying bacteria
Sulfate reducers

Answer 1

a)

-Various methods can be used to identify the bacterial activity in the water of lake are given as follow:

i) Culture and Infectivity assay of Bacteria- It involve culturing the microbe from specific volume of water using enrichment media. Identification of cultured bacteria can be identified by using either subculturing on other differential and selective media, biochemical, metabolic and other phenotypic analyses or immunological analyses.

ii) Pour Plate Method: It involve dilution of original sample followed by the bacteria growing colony on nutrient media so the number of colonies on the plate can be counted.

- Fraction of bacteria that are metabolically active in Lake water can be estimated by using Staining methods: CTC (5-cyano-2,3-ditolyl tetrazolium chloride), DAPI (4′,6-diamidino-2-phenylindole) staining followed by a propanol wash, and the Molecular Probes Live/Dead stain.

- Particular group of microrganism can be identified using various staining method, more often 16S rRNA sequencing can be used for bacterial identification. Later the number of bacteria can be identified using standard or viable, Plate Count Method and Spectrophotometric (turbidimetric) analysis.