Halocins: are they involved in the competition between halobacteria in saltern ponds?

Abstract

Many representatives of the family Halobacteriaceae ("halobacteria") excrete halophilic bacteriocins (halocins) that inhibit the growth of other halobacteria. In spite of the fact that halocin production is widespread among the Halobacteriaceae, no information is available on their ecological significance. To test whether halocins may play a role in the interspecies competition between different types of halobacteria in saltern crystallizer ponds inhabited by dense communities of these red halophiles, we assayed for halocins active against a variety of halobacteria in salterns from different locations worldwide. Detection of halocin activity was based on the inhibition of growth of indicator organisms on agar plates, the decreased incorporation of radiolabeled substrates, and microscopic examinations. No halocin activity was detected in any of the brines examined, in spite of the fact that halocin production was demonstrated in cultures of most microorganisms isolated from these brines. Thus, the contribution of halocins in the competition between different halobacteria in hypersaline aquatic environments is probably negligible.

The Sulfolobicin Genes of Sulfolobus acidocaldariusEncode Novel Antimicrobial Proteins

“…These halocins are not homologous to sulfolobicin. The production of halocins by halophilic euryarchaea is a common process, although their precise ecological role is elusive (13). The release of antimicrobial polypeptides targeted at related species therefore seems to be a common FIG.…”

“…Archaea produce so-called archaeocins, but until now only a few of these antimicrobial (poly)peptides have been described (14,16,17). Halocins are archaeocins that are produced by halophilic euryarchaea (13). Some halocins, such as halocin H4, have a rather narrow activity spectrum, whereas halocin A4, for instance, is a broad-spectrum antimicrobial agent that is also active against thermoacidophilic crenarchaea (10,16).…”

Study on the Production and Re-use of Poly(3-hydroxybutyrate-co-3- hydroxyvalerate) and Extracellular Polysaccharide by the Archaeon Haloferax mediterranei Strain DSM 1411

“…Apart from the utilization of archaea for bioleaching to mine valued metals from diverse ores, these ancient cellular factories have also the potential to provide a broad number of marketable bio-products by conversion of various raw materials. The following groups of compounds are anticipating their market launch: Bacteriocins to be used as antibiotics 1,2,3,4,5 , bacteriorhodopsin pigments for biosensors 6,7 , enzymes resistant under extreme conditions 8 , and, most of all, biopolymers to be used in the food industry (extracellular polysaccharides, EPS) or for production of "bioplastics", namely poly(hydroxyalkanoates) (PHA) 8 .…”

The Family Halobacteriaceae

“…mediterranei (Cheung et al 1997). Although the ability to excrete halocins may be expected to be of considerable ecological advantage, no data are available as yet that prove that halocins are excreted by natural communities of halophilic Archaea in concentrations sufficient to inhibit the development of competitor strains, thus substantiating their ecological role (see Kis-Papo and Oren 2000).…”