Abundance of heterotrophic aerobe bacteria (HAB) adsorbed on Granite, Basalt and Migmatite rock fragments immersed in wells in Central Africa: Temporal variation and assessment of the hierarchical influence of some abiotic factors

Abstract

This study aimed at assessing the daily abundance of heterotrophic aerobe bacteria (HAB) adsorbed on fragments of Granite, Basalt and Migmatite immersed in two wells W1 and W2 on the one hand and the contribution of some abiotic factors on this process on the other hand. The incubation durations of rock fragments immersed were 4, 8 and 12h. In W1, the abundance of bacteria adhered on the Basalt varied between 2x102 and 2.3x104 CFU/cm2 after 4h, between 4x102 and 1.3x104 CFU/cm2 after 8h, and between 1.7x103 and 1x105 CFU/cm2 after 12h. On the Migmatite, it ranged from 9x102 to 2.7x104 CFU/cm2 after 4h, from 3.6x103 and 2.4x104 CFU/cm2 after 8h and from 4.4x103 and 8.8x105 CFU/cm2 after 12h. On the Granite, the abundance after 4, 8 and 12h varied between 4x102 and 4.1x104, between 2x102 and 1.3x105 and between 4.2x103 and 7.3x104 CFU/cm2 respectively. In W2, the abundance of cells adsorbed after 4h ranged from 1.1x103 to 1.3x105 CFU/cm2 on the Basalt, from 8x102 to 2.2x104 CFU/cm2 on Migmatite and from 9x102 to 6.2x104 CFU/cm2 on the Granite. After 8h, it ranged from 5x102 to 1.2x104 CFU/cm2 on the Basalt, from 4x104 to 2.5x104 CFU/cm2 on the Migmatite, and from 9x102 to 3.9x104 CFU/cm2 on the Granite. After 12h, it fluctuated between 6x102 and 9.8x104 CFU/cm2 on the Basalt, 5x103 and 1.9x105 CFU/cm2 on the Migmatite, and 1.3x102 and 1.5x105 CFU/cm2 on the Granite. Using the power function law, it was noted that the process was mainly controlled by depth of water column (DWC), suspended solids, electrical conductivity (EC), and the amount of bacteria adhered after the first 4h incubation on Basalt, the color and turbidity on Granite, and by the DWC and EC on Migmatite. The dominant factors varied from one rock to another, and the hierarchy order undergoes temporal variation.