Biology of moderately halophilic aerobic bacteria

Abstract

The moderately halophilic heterotrophic aerobic bacteria form a diverse group of microorganisms. The property of halophilism is widespread within the bacterial domain. Bacterial halophiles are abundant in environments such as salt lakes, saline soils, and salted food products. Most species keep their intracellular ionic concentrations at low levels while synthesizing or accumulating organic solutes to provide osmotic equilibrium of the cytoplasm with the surrounding medium. Complex mechanisms of adjustment of the intracellular environments and the properties of the cytoplasmic membrane enable rapid adaptation to changes in the salt concentration of the environment. Approaches to the study of genetic processes have recently been developed for several moderate halophiles, opening the way toward an understanding of haloadaptation at the molecular level. The new information obtained is also expected to contribute to the development of novel biotechnological uses for these organisms.

FIG. 1

Biosynthetic pathway for ectoine and hydroxyectoine based on enzymological studies. The proposed formation of hydroxyectoine (dotted line) from ectoine is still hypothetical. Modified from reference with permission of the publisher.

FIG. 2

Restriction maps of four plasmids and two derivative cloning vectors from the moderately halophilic bacteria H. elongata ATCC 33173 (A), C. marismortui ATCC 17056 (B), H. elongata ATCC 33174 (C), S. costicola E-367 (D), pHE1 derivative (E), and pCM1 derivative (F). Reprinted from references , , , , and with permission of the publishers).

FIG. 3

Deletion analysis of the replicon of plasmid pCM1. (A) Schematic illustration of the organization of the 1.6-kb basic replicon. (B) Consequence of deletions on replication. + able to replicate; +(pCM1), able to replicate only in the presence of pCM1; −, not able to replicate; ±, defective replication. Reprinted from reference with permission from the American Society for Microbiology.