Molecular dissection of bacterial acrylate catabolism--unexpected links with dimethylsulfoniopropionate catabolism and dimethyl sulfide production.

A bacterium in the genus Halomonas that grew on dimethylsulfoniopropionate (DMSP) or acrylate as sole carbon sources and that liberated the climate-changing gas dimethyl sulfide in media containing DMSP was obtained from the phylloplane of the macroalga Ulva. We identified a cluster that contains genes specifically involved in DMSP catabolism (dddD, dddT) or in degrading acrylate (acuN, acuK) or that are required to break down both substrates (dddC, dddA). Using NMR and HPLC analyses to trace 13C- or 14C-labelled acrylate and DMSP in strains of Escherichia coli with various combinations of cloned ddd and/or acu genes, we deduced that DMSP is imported by the BCCT-type transporter DddT, then converted by DddD to 3-OH-propionate (3HP), liberating dimethyl sulfide in the process. As DddD is a predicted acyl CoA transferase, there may be an earlier, unidentified catabolite of DMSP. Acrylate is also converted to 3HP, via a CoA transferase (AcuN) and a hydratase (AcuK). The 3HP is predicted to be catabolized by an alcohol dehydrogenase, DddA, to malonate semialdehyde, thence by an aldehyde dehydrogenase, DddC, to acyl CoA plus CO2. The regulation of the ddd and acu genes is unusual, as a catabolite, 3HP, was a co-inducer of their transcription. This first description of genes involved in acrylate catabolism in any organism shows that the relationship between the catabolic pathways of acrylate and DMSP differs from that which had been suggested in other bacteria.

Evidence of rickettsial disease agents in ticks from Ethiopian cattle.

Evidence has recently been accumulating that domestic animals may play an ancillary role in rickettsial zoonoses. In particular, attention has been focused on the activity of Rickettsia prowazekii in Egyptian and Ethiopian livestock and their ticks. An attempt has now been made to confirm previous findings of R. prowazekii in the sera of zebus, sheep and goats in Ethiopia, which brought epidemic typhus into the category of a zoonosis. This attempt was not successful, but tests did indicate that some ticks were infected with R. conori (boutonneuse fever or tick-borne typhus) and Coxiella burneti (Q fever), this being the first evidence for the existence of these agents in Ethiopia.Antibodies against R. conori were found in significant numbers in the sera of sheep and goats from one locality, but Q-fever antibodies were surprisingly rare.