The Diversity of Bacteriocins in Gram-Negative Bacteria - Allelopathy is the production of chemical compounds which are toxic to other organisms but not to the producers of these compounds. For microorganisms, there is a wealth of data demonstrating that allelopathy is an important mediator of intra- and inter specific interactions and consequently, a significant factor in maintaining microbial biodiversity (Chap. 6, this volume). In bacteria,these allelopathic substances include metabolic by-products such as ammonia or hydrogen peroxide; the ‘classical’ antibiotics such as bacitracin and polymyxin B, lysozyme-like bacteriolytic enzymes and the bacteriocins.
 |
| The Diversity Bacteriocins (sumber: http://jb.asm.org/) |
The bacteriocins produced by Gram-negative bacteria are diverse. Over 30 bacteriocins from Escherichia coli have been identified and, undoubtedly, more have yet to be discovered. The diversity present in other Gram-negative species, including other members of the Enterobacteriaceae, is largely unexplored. The molecular mechanisms by which this diversity has arisen, at least for that class of bacteriocins known as colicins, is well understood and is discussed elsewhere (Chap. 3, this volume). However, the factors influencing the frequency of bacteriocin production and the diversity of bacteriocins in populations of bacteria are largely unknown. Acquiring this knowledge is essential, not only if we are to understand the role bacteriocins play in shaping bacterial communities in natural environments but also because there is an increasing desire to exploit bacteriocins to solve a range of applied problems.
As a consequence of the rising incidence of resistance to most traditional antibiotics, numerous research programs have been implemented aiming to explore the potential role which naturally produced and genetically modified bacteriocins might have as replacements for traditional antibiotics (Gillor et al. 2004). Other efforts focus on the use of antimicrobial toxins as food preservatives (Gillor et al. 2004). There is also an ever-increasing interest in he use of bacteria as biocontrol agents for the management of fungal and bacterial plant pathogens and, more recently, as the active agent in probiotic formulations. Probiotic therapy is a disease prevention strategy used in humans and domesticated animals, as well as a procedure considered to enhance the growth rate of livestock and poultry. The basis of the method is to ensure the establishment of ‘good’ bacteria in the gastro-intestinal tract in order to prevent the establishment of bacterial pathogens. One of the most important attributes of a ‘good’ probiotic strain is thought to be the strain’s ability to produce antimicrobial compounds. However, the successful use of bacteria as biocontrol agents will require a sound understanding of microbial ecology and the factors influencing the frequency of bacteriocin production and diversity in populations of bacteria. Thus, the aim of this chapter is not to describe the diversity of bacteriocins which have been characterised from Gram-negative bacteria but, rather, to identify and discuss some of the factors observed to influence bacteriocin diversity. As usual, much of the data relates to bacteriocin production in E. coli but reference will be made also to observations concerning other species of the Enterobacteriaceae. The material presented has largely not been published previously, and is based on phenotypic and genotypic surveys of bacteriocin production in three collections of E. coli. The first of these collections consists of 496 isolates taken from a variety of mammal species living throughout Australia. The methods used to isolate and characterise the strains in this collection have been described by Gordon and Cowling (2003). The second collection consists of 266 faecal isolates recovered from people living in the Canberra ACT region of Australia, the isolation and characterization of these strains having been described by Gordon et al. (2005). In addition to the human faecal isolates, the collection contains 353 isolates recovered from extra-intestinal body sites of people. The third dataset was collected and characterised using the same methods as those used for the other two, and consists of 208 strains recovered from soil, water and sediment samples from a variety of localities across Australia. All strains in the three collections have been screened using a PCR-based approach for the presence of 29 virulence-associated traits and to determine their E. coli group membership (A, B1, B2, D), as described by Gordon et al. (2005). The majority of the strains have been screened using a combination of phenotypic and genotypic approaches in order to determine the frequency of bacteriocin production and the types of bacteriocins present in these strains, using the methods described by Gordon and O’Brien (2006).
Posting Komentar