Introduction
The variation in phenotype amongst all organimsis can be produced by genetic different and ifluences from the environment. Whilst this field is widely and effectively investigated, Phase variation remains significantly untouched in the field of research. (Astauroff, 1930; Falconer and Mackay, 1996). Phase variation, being the difference in phenotypgic expression caused by the effect of environmental factors on the expression of the genetic potentials is what this paper is centred around.
Phenotypes are visible characteristics of an organism. The study of bacterial phenotypes, such as growth properties, aid in growing them in vitro, diagnosing them in various conditions and infectious diseases and using them for microbial technology.
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In comparison with animal and human genomes, a bacterial genome is usually smaller. The range is from 130 kbp to more than 14 Mbp (Bassi, 1990). Gene sequencing technique shown a very high correlation between the number of genes and genome size of bacteria.
The bacteria that will be experimented on in this paper is Pseudomonas fluorescens. P. fluorescens has been regarded as nonpathogenic for humans,(A. Baader and C. Garre(1887)) However, it has been discovered that P. fluorescens can cause acute infections in humans and has been reported in clinical samples from the mouth, stomach, and lungs.
The mutation of the homologous gene in the bacterium results in a loss of competitive root colonization (Dekkers, L. C., C. C. Phoelich, L. Van der Fits, and B. J. J. Lugtenberg. 1998). This implies that phase variation might play an important role in the colonization of this heterogeneous and changing ecosystem
As environments change, Pseudomonas fluorescens F113 undergoes phenotypic variation, resulting in a different appearance of colonies with different morphologies and this is what will be investigated in this paper.
The aims of the experiment are to observe the variation of colony morphologies and use staining to distinguish between the different bacteria. Pseudomonas fluorescens will be cultured in a kings medium and the concentration of magnesium sulfate will be halved.
The magnesium sulfate is probably best interpreted as being required for growth and, therefore, beneficial to bacterial accumulation on the agar plate (Slininger and Jackson, 1992). This change in the concentration should affect the diversity of morphologies and appearancs of colonies.
Methods
In groups of two, 50 μl of P. fluorescens was pipetted into a tube containing 5 ml of KB medium. In another tube, 50 μl of P. fluorescens was added to 5 ml of KB medium that contained xylose instead of glycerol. Caps were loosely fitted top using tape over them. The tubes were incubated under static conditions at 28 °C for seven days in vials. In the petri dishes, they were incubated for four days and then left at room temperature for three days. Both tubes were then examined and observations of both were noted. Serial dilutions were carried out on both cultures so that 0.01%, 0.0001%, 0.00001% and 0.000001% suspensions were made (these suspensions were labelled 1 to 4 in order of decreasing concentration). 50 μl of suspensions 2 to 4 for both cultures were plated. These were incubated for one week under the same conditions as above. The plates were examined and each discrete colony was named, based on there morphology, and counted. Simpson’s index of concentration was used to calculate the diversity of the bacteria. Gram staining was then carried out to determine if any colonies were present due to contamination. Lastly, the Wilcoxon Mann-Whitney U test was also carried out on the data.
Discussion and Conclusions
The Mann-Whitney U test is used to compare differences between two independent groups. The Z value that was obtained was 2.64584 and as this value is greater than 1.96, the null hypothesis, which is that the change in concentration of magnesium sulfate doesn’t not have an effect on the diversity of Pseudomonas fluorescen, must be ignored.
There is a very plausible explanation for this rejection of the null hypothesis. Magneisum sulfate promotes and causes growth. Therefore, reduction of magnesium sulfate in the variable will affect the morphology and diversity of the bacteria.
Sulfate-dominated systems show greater water activities and, therefore, are expected to be very favourable for life(Hallsworth et al., 2003; Marion et al., 2003; Grant, 2004). For instance, while Basque Lake has approximately the same salinity (25%) as the Dead Sea and Great Salt Lake, the water activity of Basque Lake (0.919) is much higher than that of the Dead Sea (0.690) or Great Salt Lake (0.776) as there is a greater concentration of sulate ions in the water.
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