DETERMINATION OF BACTERIAL LOAD AND DIVERSITY IN SELECTED SITES IN LAKE NAKURU, KENYA AND THEIR ABILITY TO DEGRADE PLASTICS AND PETROLEUM OIL

Abstract

Halophilic bacteria have been largely omitted from ecosystem studies of saline Lakes, especially with regard to their importance in decomposition process under aerobic conditions. Plastics are widely used as packaging material due to their light weight, inertness and low cost. The disposal of plastics has become a major environmental challenge because they are not easily degraded. Petroleum oil released into the environment is a world wide problem because it contains aromatic compounds that are toxic to most life forms. Episodic and chronic pollution of the environment by petroleum oil causes major ecological perturbations. Petroleum oil spills affects many species of plants and animals in the environment, as well as humans. This research project was carried out to determine the load and biodiversity of bacteria in five selected sites of Lake Nakuru and to establish their ability to degrade disposable plastics and petroleum oil. Water samples were collected in sterile bottles from five sites of Lake Nakuru namely; Middle Lake, Makalia, Enderit, Njoro and Hippopoint. Serial dilution was carried out and culturing was done using spread plate method on nutrient agar. The cultures were incubated at 35 C for 24 hours. Bacterial load was determined by counting the number of colony forming units. Sub-culturing was done to obtain pure cultures which were then isolated and stocked in agar slants and brain heart infusion media. Identification of bacteria was carried out by observing morphological characteristics, gram staining, biochemical tests, and serotyping using Analytical Profile Index Kits. Degradation of plastics experiment was determined by percentage weight loss of the materials. The experiment had four replicates and was carried out for 90 days. A "greasy spot" test was carried out for seven weeks to determine oil degradation. A total of twenty one isolates were identified; two bacteria were gram positive while nineteen were gram negative. Various bacteria were able to degrade plastics and petroleum oil. They included Sphingomonas paucimobilis, Streptococcus pyogenes, Tatumela ptyseas, Bacillus anthracoides, Chryseobacterium indologenes, Chryseobacterium meningosepticum, Pseudomonas cepacia, Proteus penneri, Moraxella sp., Alcaligen sp., Providencia stuarti, and Providencia rettgeri. Yersinia pseudotuberculosis degraded petroleum oil but was unable to degrade plastics. In this study the bacteria that have not been reported in biodegradation of plastic and oil included Tatumella ptyseas, Proteus penneri and Providencia stuarti. These bacteria are recommended in bioremediation of oil spills and in the biodegradation of plastics. This will result in broad applicability, low cost and low risk of exposure to hazardous chemicals during clean up.