Distribution of heterotrophic aerobic marine bacteria in sediment in Eastern Harbour of Alexandria

Abstract

In Eastern Harbour (EH) of Alexandria (Egypt), where an under-water museum is planned to be built, the distribution of some heterotrophic bacteria and their relationships to physical parameters and biochemical composition of the sedimentary organ ic matter were investigated. The Eastern Harbour is a relatively shallow semi-closed basin and is sheltered from the sea by an art ificial breakwater leaving two openings, El-Boughaz and El-Silsila. Seven stations covering the area of the EH were selected and surface sediments were collected seasonally from spring to winter 2002. The near bottom temperature varied seasonally with a minimum value in winter and a maximum in summer. In contrast to the temperature values, dissolved oxygen exhibited maximum values in cold seasons. The seasonal average of the total organic carbon ranged from 0.48 ± 0.16 to 4.42 ± 2.46%, while the total organic nitroge n ranged from 0.07±0.08 to 0.42±0.38%. The total carbohydrate had minimum and maximum values of 273 μg g−1 and 6539 μg g−1. The combined amino acids represented the dominant biochemical class of organic matter in the EH sediments with an average of 365 ± 1911 μg g−1. The total bacterial count ranged from 1.4 × 104 to 1.4 × 107 colony forming unit (CFU) g−1 sediment dry weight. Amylolytic bacterial group was recorded in almost all sites and seasons, while proteolytic bacteria were dominant in spring and au tumn. The variation in the abundance of amylolytic and proteolytic bacterial groups was found to be parallel to the variation in soluble carbohydrates and free amino acids. High percentage of H2S-producing bacteria was reported during summer at some stations confirming the low oxygen content of the sediment at these sites. Agar-degrading bacteria were found only in warm seasons. The count of co liform bacteria in the EH sediments was very low (<10 CFU g−1) during all monitored seasons indicating that the EH marine environment was almost free of domestic waste discharge during this period.