Document Type


Date of Award



College of Science, Engineering, and Technology (COSET)

Degree Name

MS in Environmental Toxicology


• Bacteria isolates • Soil bacteria • Soil Bacteria Identification • Soil Bacteria in Houston • Soil Bacteria in Houston watershed • Soil Bacteria in Houston' soil


Any major flooding event in a heavily populated urban area can lead to significant health risks. Stagnant water can cause pollution to leak into water and soil such as chemical and biological contaminants. Some of these pollutants will solubilize into the water, while other contaminants will stick in the soil. Harmful biological and chemical agents in floodwater and soil could affect human health. Chemical agents like polycyclic Aromatic Hydrocarbons (PAH), pesticides, and heavy metals are some of the contaminants found in the soil of watershed banks. Furthermore, biological agents such as bacteria, fungus, parasites, and viruses can cause detriment to the health of humans and the environment (Murtaza et al.,2014).

In this study, bacteria isolates were obtained from the soil of the following bayou and creek banks; Dickinson, Cypress Creek, and Horsepen bayou located near Houston Texas. The samples were taken by triplicate from different point sites during the summer and fall of 2018. From the pool of samples, ten unknown samples were taken for isolation. After the preliminary screening and biochemical test, the samples were

subjected to the Partial 16S rDNA gene sequencing and Biolog testing, which was used for further identification of the microorganisms. All ten bacteria were genetically identified. The most relevant bacteria for human health risks were Pseudomonas putida and Pseudomonas fluorescens.

These two-gram negative bacteria were monitored for growth and biofilm in the presence of different concentrations of lead (Pb) over time. P. putida was significantly impacted by lead between 4-8 hours period of exposition. P. fluorescens, shows similar patterns over the 5 to 12 hours period.

Regarding the biofilm production, P. putida was formed during a 6-hour time-lapse, which showed significant impact (p<0.05) when compared with the Pb concentration against the control. In contrast, P. fluorescens biofilm formation was visualized between 6h -12 h. At 6 hours, the biofilm production increased significantly in the bacteria with lead treatment than without Pb (0 ppm). Interestingly, at 12 hours of time-lapse, as the concentration of Pb increased (≥600 ppm), bacteria became very sensitive to Pb treatment, and the biofilm formation was drastically reduced (p<0.05).

The findings in this study show that these two types of Pseudomonas species have different responses when in contact with heavy metals like lead, which can negatively impact the ordinary communities of microorganisms in the soil.