MICROBIAL COMMUNITY AND ITS ROLE IN MANGROVE ECOSYSTEM

Abstract

The aim of current experimental work was to explore the importance of microbial mat present at the mangrove area of Sandspit backwaters, Karachi. The first chapter consists of an introduction to mangroves in general. In chapter 2, nutrients in the backwater channels were studied. It was found that nutrient levels were more on site where mat was present as compared to without mat site. Overall phosphate levels were high throughout all seasons and the nutrient levels were found in the following order phosphate>ammonium>nitrate>nitrite. In chapter 3, it was observed that the presence or absence of microbial mat directly influence the soil. The soil covered with mat have increased water retention, low salinity and pH, high carbon as compared to soil without mat. In chapter 4, the seasonal rates of potential nitrification were examined. This process is a significant step in nitrogen cycle and involves the conversion of ammonium into nitrate. Although there were no drastic changes in rates with respect to seasons, the presence of microbial mat significantly affects the rates of potential nitrification. In chapter 5, microbial mats were surveyed. The primary members of mat include few protozoa, cyanobacteria, bacteria and diatoms. The filamentous forms of cyanobacteria were responsible for macroscopic green sheath formation on top soil. Phormidium tenue, Spirulina labyrinthiformis, Spirulina major, Oscillatoria limosa, Phormidium breve and Oscillatoria prínceps were present in all seasons. In chapter 6, cyanobacterial metabolites were inspected. Seawater fraction of Aphanocapsa litoralis and ethanol fraction of Phormidium breve were active against Candida albicans. Phormidium breve extract was more cytotoxic (LC50 0.02 mg/ml) against Artemia salina as compared to Aphanocapsa litoralis extract (LC50 6.2 mg/ml). In chapter 7, metabolites of bacteria associated with microbial mat were screened. Out of 120 isolates only two isolates SSC1407 (Proteus sp.) and SSC14011 (Klebsiella pneumoniae strain) were found to have some antagonistic activity against isolates of E. coli and Proteus O respectively. SSC1407 tolerated increased levels of temperature and different types of chemicals. SSC14011 tolerated high pH, UV-rays and also produced higher protein yield after successive purifications. SSC14011 was slightly more cytotoxic (LC50 0.046 mg/ml) against Artemia salina than SSC1407 (LC50 0.052mg/ml).