Characteristics and Living Patterns of Marine Myxobacterial Isolates

Abstract

The growth, morphology, and life cycle of two marine myxobacterial isolates, halotolerant Myxococcus fulvus strain HW-1 and halophilic Haliangium ochraceum strain SMP-2, were studied as models to determine the living patterns of myxobacteria in the ocean. The growth, morphology, and development of halotolerant strain HW-1 shifted in response to salinity. The optimal seawater concentration for growth of HW-1 was 0 to 80% (salinity, 0.1 to 2.9%), and the strain grew poorly in media with a salinity of more than 4%. The cells became shorter as the seawater concentration increased. The fruiting body structure was complete only on agar prepared with low concentrations of seawater or salts (less than 60% seawater; salinity, 2.1%), and rudimentary structures or even simple cell mounds appeared as the seawater concentration increased. In contrast, the halophilic strain SMP-2 was unable to grow without NaCl. The cell length and the morphology of the fruiting body-like structure did not change in response to salts. In seawater liquid medium, the cells of both strains were confirmed to be able to form myxospores directly from vegetative cells, but they could not do so in medium containing a low seawater concentration (10% or less). HW-1 cells from medium containing a high concentration of seawater grew independent of cell density, while cells from medium containing a low concentration of seawater (10% or less) showed density-dependent growth. SMP-2 cells showed density-dependent growth under all salinity conditions. The results suggest that the halotolerant myxobacteria are the result of degenerative adaptation of soil myxobacteria to the marine environment, while the halophilic myxobacteria form a different evolutionary group that is indigenous to the ocean.Gram-negative unicellular myxobacteria are phylogenetically located in the ␦ division of the Proteobacteria (19-21, 24), and they are notable among prokaryotes for their complicated social behavior (2, 18). Myxobacterial cells move by gliding in swarms on solid surfaces, feed by cooperatively digesting macromolecules as well as whole microorganisms, and form multicellular fruiting bodies on solid surfaces. The resting cells, or myxospores, develop within fruiting bodies. Fruiting bodies develop only on solid surfaces (18), and terrestrial myxobacteria do not usually tolerate an NaCl concentration greater than 1% (15). The myxobacteria are typically considered to be soil microorganisms and are common in many terrestrial environments (1, 14). On the other hand, myxobacteria can be isolated from marine samples (6,7,8,9,13,14,25), as proven by the 16S rRNA gene fragments amplified from marine samples (4, 11) and permanently cold marine sediments (12). Depending on their adaptation to salinity, the marine myxobacterial isolates include three types: nonhalotolerant isolates, halotolerant isolates, and halophilic isolates. The nonhalotolerant isolates are the isolates that are unable to grow with a salt concentration greater than 1.0% (15). They are presumed to have germinated...

Biogeography and phylogenetic diversity of a cluster of exclusively marine myxobacteria

“…All these species originate from coastal regions of Japan and affiliate to the suborder Nannocystineae. Halotolerant and halophilic myxobacteria appear to differ with respect to the formation of fruiting bodies, and the adaptation of their life cycle to the salty environment (Zhang et al, 2005). Selected strains of Myxococcus form fruiting bodies also in sea water media (Wang et al, 2007).…”

Hdsp, a horizontally transferred gene required for social behavior and halotolerance in salt-tolerant Myxococcus fulvus HW-1

“…Figure 1d demonstrates the morphological characteristics of YLH0401 and HW-1 on TPM plates. Concurrently, the salt tolerance of YLH0401 also decreased; although HW-1 cells were able to grow in 130% HVY or 3% NaCl (Zhang et al, 2005), mutant cells were able to grow only in 30% seawater (30% HVY, VY-2 (Reichenbach and Dworkin, 1992) prepared in 30% seawater) or 1% NaCl. Therefore, the insertion mutation in YLH0401 produced a series of phenotypic changes related to both salt tolerance and social behavior.…”

“…When cultured in a low concentration of saltwater, the strain exhibits a culture phenotype similar to soil myxobacterial strains, such as developing fruiting bodies and myxospores in response to starvation on solid surfaces. However, when the saltwater concentration is increased, the strain changes its living pattern by forming myxospores directly from vegetative cells (Zhang et al, 2005). These characteristics make HW-1 an ideal model for studying the adaptation mechanisms of salt-tolerant myxobacteria to marine environments.…”

“…However, some halophilic and halotolerant myxobacterial strains have been isolated from marine environments (Iizuka et al, 1998(Iizuka et al, , 2003aFudou et al, 2002;Li et al, 2002). On the basis of phylogenetic analyses and living patterns, the halophilic myxobacteria are considered to be indigenous to the ocean, whereas the halotolerant myxobacteria are probably soil myxobacterial strains that have adapted to oceanic conditions (Zhang et al, 2005). There is much interest in understanding how salt-tolerant myxobacteria and their social behaviors have adapted to oceanic conditions.…”

New Locus Important for Myxococcus Social Motility and Development

“…In contrast to the salt sensitivity of terrestrial strains (19), salt-tolerant myxobacteria are able to withstand a wide range of salinity. In response to changes in salinity, some salt-tolerant myxobacteria show altered vegetative and developmental characteristics (29). Differences in morphogenetic characteristics appear to indicate that salt-tolerant myxobacteria are the result of the adaptation of soil myxobacteria to marine environments (29).…”