Introduction

General applications of the technique to bacterial cells

Electron probe X-ray microanalytical studies have been carried out on a wide range of bacterial cells, using a variety of preparation techniques. These studies have involved many different applications and have relevance to areas of environmental microbiology, studies on cultured cells, human pathology, plant pathology, metal toxicity and biochemical research. Some of these studies are summarised in Table 12.1, which emphasises the broad contribution that this technique has made to bacteriology.

The main purpose of this chapter is to explore the potential uses of electron probe X-ray microanalysis in bacterial research, and to consider the different experimental approaches that can be used with these cells. The chapter will concentrate particularly on bacterial pathogens of higher plants, since this has been an area of special interest in this laboratory.

Elemental composition of plant pathogenic bacteria

Plant pathogenic bacteria are facultative parasites, able to grow and multiply both outside and inside the plant – where they may cause disease. The elemental composition of these organisms is of considerable interest in relation to a number of key aspects of their existence (Sigee, Hodson & El-Masry, 1989). Changes in the concentration of specific cations, in particular, have been implicated in various functional processes – including hydrolysis of bacterial toxins (Levi & Durbin, 1986), interactions between microorganisms at the plant surface (De Weger et al., 1988) bacterial changes during disease (El-Masry & Sigee, 1989), chemical control measures (Sekizawa & Wakabayashi, 1990) and in vitro effects of heavy metals (Sigee & Al-Rabaee, 1986; Hodson & Sigee, 1991).