Bacteria substrate induction

Under normal conditions the inductor is a diffusible substance or group of substances, metabolic products of the neighboring tissue. The closer the contact, the higher the concentration of these products. For this reason the reaction of the receptor systems has not developed very narrow specificity in the course of evolution. A reaction has developed to a signal, which could be an individual compound. However, this does not mean that other compounds cannot act as such signals. Under normal conditions other compounds simply are not present, and the receptor systems have not therefore developed very narrow specificity of reaction such as occurs during the allosteric interaction of specific proteins in the phenomena of substrate induction in bacteria (see Chapter 3). 

When phosphate is the limiting factor, the induction mechanism is more difficult to deduce. However, bacteria, like all other living systems, are not able to generate ATP by phosphorylating ADP in the absence of phosphate. It seems quite plausible that, under these conditions, 2/H/ do not flow away. As in the two previously mentioned limitations, 2/H/ remain and acetyl-CoA becomes available, thus both substrates could be assimilated and deposited intracellularly as poly(3HB). 

A summary of the key information has been compiled on the anaerobic and aerobic bacteria discussed above. Comparison of the substrates for growth of these organisms (Table I) show that all utilize cellobiose and various forms of cellulose. The two species belonging to Bacteroides have different specificity for substrates, while those for Ruminococcus, Cellulomonas and Thermomonospora were the same. Table I also allows comparison of the behavior of the 13 species of cellulolytic bacteria toward cellobiose. More variability is noted in this regard and no correlation between induction/repression can be made with the mechanism of cellobiose degradation. 

In other bacteria, such as Acinetobacter, alkane oxidation genes are chromosomal (Singer Finnerty, 1984b). Moreover, some of the genes that participate in alkane oxidation probably comprise indispensable constituents of the bacterial cell. For example, in P. oleovorans, one of the gene products that catalyzes the initial oxidation of aliphatic substrates, the alkane hydroxylase, is an integral cytoplasmic membrane protein, and constitutes after induction 1.5-2% of the total cell protein (Nieboer et al. 1993). 

Larvae of the scallop Placopecten magellanicus actively selected monofilament substrates with dense coatings of bacteria, microalgae, and detritus.180 However, there was also significant settlement on noncoated monofilaments in these experiments, suggesting that preference does not imply a necessary inductive process by biofilm organisms for the scallop larvae to settle and... 

Biochemical Induct Assay (BIA) (.5,6) The semi-quantitative spot test version (not the one-tube assay for the quantitative measurement of induction) was used for most of the work. The bacteria are poured in agar with or without rat liver S9 activation mix, onto large (24 cm x 24 cm) bioassay plates. Largomycin fermentation broth or test solutions are spotted onto the plates, allowed to incubate for three hours at 37°C, and overlaid with a second agar layer containing substrate. Within five or ten minutes, areas of induction are seen as red spots of insoluble dye formed by cleavage of the colorless substrate. Rapid sampling with the wide end of pasteur pipettes allows an operator to spot 100 samples on two plates in 20 minutes. 

Figure 1. Patterns of substrate disappearance related to mechanism of adaptation. Genetic changes such as mutation, plasmid exchange, or recombination (A). Growth of a small population of bacteria able to degrade the test chemical immediately (B). Delayed induction of enzymes or activation of specific organisms (C).

Karube [389] has pioneered in the development of many bacterial electrodes based on this principle using various bacteria depending on the target analyte. Ion-selective electrodes for NH3, O2, CO2, H2S and have all been used in conjunction with immobilized whole cells. Riedel et al. [390] have recently demonstrated that preincubation of certain bacterial electrodes with the desired analyte (substrate) can enhance the sensitivity of a sensor toward that chemical by a factor of as much as 25. This induction approach may prove to be widely applicable. The shelf-life of a wholecell electrochemical sensor can extend up to several weeks with fully optimized storage conditions (low temperature, for example). Microbe thermistors (sensors that respond to the heat evolved during bacterial metabolism of a substrate) have also been developed, but these present problems once again with respect to analyte specificity,... 

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