Monitoring and Detection of Different Growth States of Thermophilic SRB

Abstract

Monitoring and Detection of Different Growth States of Thermophilic SRB

Until recently bacteria were not generally considered to be able to survive unfavourable conditions, such as lack of growth nutrients or extremes of temperatures. However, research has shown that some microbes are able to survive such inhospitable conditions by undergoing a series of responses which frequently include a reduction in cell size. These responses produce starved bacteria which are non-active forms of cells, analogous to spores, whereby they remain dormant until favourable conditions are available. It is not currently known whether microbes involved in corrosion such as sulphate-reducing bacteria (SRB), particularly thermophilic strains (t-SRB), produce starved cells. It is particularly important to determine whether they survive adverse conditions, such as temperature fluctuations or change in nutrient status, encountered within North Sea reservoirs. A twelve month laboratory research programme was undertaken to assess this possibility. From a total of nine locations in three separate fields, 54 water samples were collected and 280 enrichments were undertaken at six monthly intervals. Despite differences in water temperature, depth of the reservoirs, geographical location and geology of the formation, t-SRB were present in all except one sample. Selected cultures were subjected to various combinations of adverse conditions including the absence of growth nutrients, high or low temperatures, the presence or absence of oxygen for long periods. The ability of the cultures to survive was assessed using Most Probable Number techniques, metabolic activity, and microscopy and culture absorbance measurements. The t-SRB were able to survive all of the above combinations then grow and produce hydrogen sulphide once favourable conditions were restored. This survival mechanism has significant implications for control of microbially induced corrosion and reservoir souring.