Martin Dworkin

Isolation and Characterization of Novel Marine-Derived Actinomycete Taxa Rich in Bioactive Metabolites

ABSTRACT A unique selective enrichment procedure has resulted in the isolation and identification of two new genera of marine-derived actinobacteria. Approximately 90% of the microorganisms cultured by using the presented method were from the prospective new genera, a result indicative of its high selectivity. In this study, 102 actinomycetes were isolated from subtidal marine sediments collected from the Bismarck Sea and the Solomon Sea off the coast of Papua New Guinea. A combination of physiological parameters, chemotaxonomic characteristics, distinguishing 16S rRNA gene sequences, and phylogenetic analysis based on 16S rRNA genes provided strong evidence for the two new genera (represented by strains of the PNG1 clade and strain UMM518) within the family Micromonosporaceae. Biological activity testing of fermentation products from the new marine-derived actinomycetes revealed that several had activities against multidrug-resistant gram-positive pathogens, malignant cells, and vaccinia virus replication.

A System for Studying Microbial Morphogenesis: Rapid Formation of Microcysts in Myxococcus xanthus

A method has been found for inducing the rapid, quantitative, and relatively synchronous conversion of vegetative rods of a fruiting myxobacterium to microcysts. The conversion is induced by the addition of 0.5M glycerol to a dispersed, growing, liquid culture of Myxococcus xanthus. The vegetative rods are converted to microcysts in about 120 minutes.

Introduction to the Gliding Bacteria

The gliding bacteria are, in all likelihood, a phylogenetically heterogeneous group. The uniting character, gliding motility, may have the same taxonomic importance and reliability as flagellation. To compound the problem, we still know so little about these fascinating bacteria that our generalizations are of necessity based on relatively few observations. Thus, an organism that has lost its gliding motility may not be recognizable as a member of this group. This question may be more than theoretically important, as illustrated by the taxonomic difficulties centering around the Cytophaga-Flavobac-terium complex.

Fibrils as extracellular appendages of bacteria: their role in contact-mediated cell-cell interactions in Myxococcus xanthus.

Social behavior in the myxobacterium Myxococcus xanthus involves epicellular, peritrichous appendages called fibrils. These are polysaccharide organelles containing a set of tightly adhering proteins. It is proposed that cell‐cell contact is perceived by the fibrils and is mediated by the action of a fibrillar ADP‐ribosyl transferase. Fibrils or fibril‐like organelles have also been found on a variety of other gram‐negative bacteria and at least one archaeon, and may mediate cell‐cell contact between the bacteria themselves or between the bacteria and their eukaryotic host cells. BioEssays 21:590–595, 1999.

The Order Myxobacterales

The myxobacteria appear to be a phylogenetically uniform group with the following common characters: They are Gram-negative, unicellular, gliding bacteria; their vegetative cells are rod shaped; they form fruiting bodies and myxospores; the base composition of their DNA falls in the narrow range of 66–72 mol% G+C; they are able to degrade a variety of macromolecules.

The Order Cytophagales (with Addenda on the Genera Herpetosiphon, Saprospira , and Flexithrix )

In our discussion of the gliding bacteria (this Handbook, Chapter 19), we have proposed an alternative classification to that in Bergey’s Manual of Determinative Bacteriology, eighth edition. In accordance with those ideas, this chapter will deal exclusively with unicellular gliding bacteria. All of them are Gram-negative, rod-shaped, slender cells that are often rather delicate; in some cases the cells are very short, but more often they are quite long (Fig. 1). Many organisms of this group exhibit change in cell shape, which either leads to spherical resting cells (microcysts) or results at least in highly pleomorphic populations. In contrast to myxobacteria, no complex morphological structures such as fruiting bodies are produced. As we define them, the Cytophagales include at present the following genera: Cytophaga, Flexibacter, Sporocytophaga, Sphaero-cytophagalCapnocytophaga, Microscilla, and Lysobacter (see Table 1; Fig. 1). The group is, however more heterogenous than may seem from this classification, and will certainly require the establishment of additional genera in the future.

Excreted adenosine is a cell density signal for the initiation of fruiting body formation in Myxococcus xanthus

Abstract Myxococcus xanthus is a bacterium that forms multicellular fruiting bodies in response to starvation. The initiation of fruiting body formation is cell density dependent, and we suggest that cells measure their cell density by titering the extracellular concentration of excreted adenosine. Our evidence is as follows: (1) At low cell densities fruiting body formation does not occur unless adenosine is added. (2) Norit, a substance that binds purines, inhibits fruiting body formation, and this inhibition is reversed by adenosine. (3) Cells labeled with [ 14 C]carbonate excrete [ 14 C]adenosine which is bound by the Norit. Furthermore, [ 14 C]adenosine is excreted by developing cells at a concentration that will induce fruiting body formation at low cell density. The extracellular adenosine concentration increases with the cell density over a broad range of densities. (4) Hadacidin, an inhibitor of de novo AMP synthesis, inhibits fruiting body formation, and inhibition by hadacidin can be reversed with adenosine. Adenosine also appears to be involved in the aggregation process because the shape and size of the fruiting bodies are sensitive to the external concentration of adenosine.

Cell-cell interactions in developmental lysis of Myxococcus xanthus.

The developmental events of sporulation and fruiting body formation in the prokaryote Myxococcus xanthus are preceded by a stage of massive cell death. Two phenotypically complementable strains of M. xanthus defective in developmental lysis were identified from a group of conditional sporulation mutants. Mixture of the two lysis groups resulted in full complementation of lysis, sporulation, and fruiting body formation; efficient sporulation was observed only in strain mixtures where lysis was complemented. We have identified a cell-free extract from developing cells that phenotypically complemented lysis, sporulation, and fruiting body formation in one group of mutants; the active component of this extract appeared to be tightly cell associated. The effect of the cell-free extract could be replaced by exogenously supplied glucosamine or mannosamine.

Endogenous ADP-ribosylation during development of the prokaryote Myxococcus xanthus

We examined endogenous ADP-ribosylation of proteins during the development of the prokaryote Myxococcus xanthus. In vivo and in vitro endogenous ADP-ribosylation of M. xanthus proteins was detected and the profile of modified proteins changed during development. Adenosine and nicotinamide inhibited ADP-ribosylation. Nicotinamide stimulated cells at low density to develop, in a manner similar to that previously observed with adenosine. Higher concentrations of nicotinamide inhibited aggregation. The in vivo effects of nicotinamide on developing M. xanthus cells correlate with its in vitro effects on ADP-ribosylation and the developmental profile of putative ADP-ribosylation substrates. These results suggest that ADP-ribosylation may regulate developmental proteins in M. xanthus.

ADP‐ribosylation by the extracellular fibrils of Myxococcus xanthus

The isolated, extracellular fibrils of the myxobacterium, Myxococcus xanthus, are capable of carrying out ADP‐ribosylation. The substrate for the ADP‐ribosylation is reactive with monoclonal antibody 2105, which has been shown to be directed specifically against the integral fibril proteins. The extracellular fibrils thus contain both the ADP‐ribosyl transferase and the substrate for the ribosylation. This process may play a role in the contact‐mediated cell–cell interactions that are an important part of the social behaviour of M. xanthus.