Introduction
Bacteria rarely exist as isolated cells in nature rather aggregate into films and mats. Bacterial biofilm formation follows a developmental plan influence by environmental signals that require higher level of organizations of cells. Interactions within this special environment may confer new properties on the bacteria, such as altered metabolic activities and increased resistance to Antimicrobial agents. Biofilms have been implicated in infectious diseases, persistence of pathogens in environment and decreased productivity in affected industries At the same time they have been utilized to some extent in water purification and water treatment.
OBJECTIVES
1. To characterize the biofilm from microbial collection.
2. To count the number of each organism and use these numbers to estimate various measures of diversity.
3. To identify the number of organisms present in the biofilm.
METHODOLOGY
1. Take two microscope slides to make a slide set; mark date or place code on both of them (or else write collecting date and place code in your field notebook).
2. Put the two microscope slides back-to-back with dates on the inside surfaces.
3. Tie wire or nylon around them as if you were wrapping a package.
4. Find a place in estuary where rocks are coated black. The black is usually manganese. (The best place to look is in the shallow part of the estuary where the water flows swiftly.
5. Tie loose end of wire around mangrove tree roots (best), or bamboo skewers (skewers are less likely to be noticed and disturbed), and leave the slides there.
6. Tie flagging to a nearby tree so you can find your samples again (tie loosely so as not to hurt the tree).
7. Come back 2-6 weeks later and retrieve your slides. (Remember to take the flagging away when you are done.) Make sure you leave the slides in the zone of oxidation.
Microbial Biofilm
RESULTS
- Estimation of various measures of biodiversity
- Species richness (S) the total number of different organisms present. It does not account the proportion and distribution of each species within the local community. All you do is count the number of species found in community (number of species found in biofilm plate) however this does not indicate how the diversity of the population is distributed or organized.
- Simpson Index (D) a measurement that accounts for the richness and the % of each species from a biodiversity sample within a local community. The index assumes that the proportion and distribution of individuals in an area indicate their importance to diversity. This will help us understand the profile of biofilm organisms and their colonization pattern.
a. Calculate Pi which is the number of a given species/total number of organisms observed.
b. Simpson index: D=sum (Pi2) probability that 2 randomly selected individuals in the community belong to same category (eg. Species)
c. Simpson index of diversity: 1-D.The probability that 2 selected individuals in a community belong to different categories (e.g. species)
d. Simpson’s reciprocal index: 1/D. The number of equally common categories (species) that will produce the observed Simpson’s index
D is influenced by 2 parameters-the equitability of % of each species present and richness. For a given species richness D will decrease as the % of species becomes more equitable. The examples illustrate how these 3 indices are influenced by these 2 parameters. The researcher must observe the species patterns carefully to interpret values effectively.
Shannon-Wiener index (D) similar to Simpson index taking into account species richness and proportion of each species also known as Shannon index
- Shannon-Weiner Index. (H) The index is computed from –sum of Pi multiplied by the log of the number:
H=-sum (Pilog [Pi] (for any base)
H=-sum (Pilog [Pi] (natural log)
D. Evenness (E) : Using species richness (S) and Shannon-Weiner Index (H), evenness (E) is computed. Evenness measure how similar the abundances of different species are. When there are similar proportions of all species then evenness is one, but when the abundance is very dissimilar then the value increases
E= H/log (S)
- A comparison of one or all of these measures of biodiversity can illustrate changes in water quality conditions within a local community. Water quality parameters like light penetration, length of exposure, turbulence, DO, salinity can have dramatic impacts on levels of biodiversity.
Species Name | Number Found | Pi | Pi2 | Pilog[Pi] | Measure | Value |
Sp 1 | S | |||||
Sp 2 | D | |||||
Sp 3 | 1-D | |||||
Sp 4 | 1/D | |||||
Sp 5 | H | |||||
Total | E |
See what happens when you change the number of organisms for each of the species. Enter your own counts and find out what effect your changes have on the various biodiversity measures. Remember counts are integers.
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