Transcriptomic analysis of cobalt stress in the marine yeast Debaryomyces hansenii.

The yeast Debaryomyces hansenii overproduces riboflavin upon exposure to subtoxic levels of cobalt (Co(+2)). However, mechanisms for survival have yet to be studied and have been hindered by D. hansenii's high genetic heterogeneity among strains. In this study, we used transcriptomic analyses and RNA-seq in order to identify differentially expressed genes in D. hansenii in response to cobalt exposure. Highly upregulated genes under this condition were identified to primarily comprise DNA damage and repair genes, oxidative stress response genes, and genes for cell wall integrity and growth. The main response of D. hansenii to heavy metal stress is the activation of non-enzymatic oxidative stress response mechanisms and control of biological production of reactive oxygen species. Our results indicate that D. hansenii does not seem to be pre-adapted to survive high concentrations of heavy metals. These organisms appear to possess genetic survival and detoxification mechanisms that enable the cells to recover from heavy metal stress.

Bacteria associated with toxic clonal cultures of the dinoflagellate Ostreopsis lenticularis.

The marine toxic dinoflagellate Ostreopsis lenticularis has been implicated as the major vector in ciguatera seafood poisoning on the southwest coast of Puerto Rico. Studies have demonstrated that associated bacteria play a role in the ciguatoxin production and that different clonal cultures of O. lenticularis harbor different culturable bacteria. In this study, more than 125 associated bacteria from two toxic clonal cultures of O. lenticularis (no. 302 and no. 303) were analyzed utilizing polymerase chain reaction amplification of the partial small subunit ribosomal DNA (rRNA), denaturing gradient gel electrophoresis, and DNA sequencing. Approximately 50% of total bacteria identified in both cultures were a single species belonging to the Cytophaga-Flavobacter-Bacteroides complex. This bacterium was also found in six new O. lenticularis clonal cultures established 10 years after the original cultures used in this study and absent from a clonal culture of a different dinoflagellate species. The data presented here indicate a persistent and apparently specific association of this bacterium with O. lenticularis, which makes it a candidate involved in ciguatoxin production.

Bacterial diversity associated with the Caribbean tunicate Ecteinascidia turbinata.

The Caribbean tunicate, Ecteinascidia turbinata produces the anti-cancer agent ET-743 that could well be a metabolite of an associated bacterial strain. This current study aims at the analysis of bacteria that are persistently and specifically associated with this invertebrate. Utilizing techniques such as denaturing gradient gel electrophoresis, DNA sequencing and phylogenetic analysis of bacteria from E. turbinata collected from different locations in the Caribbean Sea, we report here the identification of five possible persistently associated bacteria. Of these, only one organism, Candidatus Endoecteinascidia frumentensis, was found specifically associated to E. turbinata from the Caribbean and has also been found to be associated with E. turbinata from the Mediterranean. These experiments suggest that assessment of bacterial diversity associated with invertebrates from different geographical sites might be an effective way of identifying persistently and specifically associated bacteria.

Culturable and nonculturable bacterial symbionts in the toxic benthic dinoflagellate Ostreopsis lenticularis.

The toxic benthic dinoflagellate Ostreopsis lenticularis hosts a variety of symbiont bacterial flora. Laboratory cultured Ostreopsis clones require the presence of symbiotic Pseudomonas/Alteromonas bacterial strains for growth and toxicity development. Three culturable bacterial strains associated with Ostreopsis were identified as Pseudomonas/Alteromonas strain 1, Pseudomonas/Alteromonas strain 2 and Acinetobacter. Denaturing gradient gel electrophoresis (DGGE) analyses of extracted Ostreopsis associated bacterial DNAs indicated that there were three culturable and four non-culturable associated bacterial strains. The results presented here are the first report of the presence of unculturable bacterial symbionts in a toxic benthic dinoflagellate. Ostreopsis lost toxicity when exposed to elevated temperatures in the field and laboratory culture and subsequently recovered toxicity at reduced temperatures. Ostreopsis associated culturable Pseudomonas/Alteromonas bacterial strains were significantly reduced in dinoflagellate cultures exposed to elevated temperatures. The decreased toxicity of O. lenticularis exposed to elevated temperatures and their subsequent recovery of toxicity in periods of reduced thermal stress may have resulted from the effects of elevated temperature on the spectrum of culturable and unculturable bacterial species interacting with their Ostreopsis host.

Identification of carbohydrate degrading bacteria in sub-tropical regions

Several bacteria from the islands of Puerto Rico, Vieques and Trinidad were isolated for their carbohydrate degrading activities. These terrestrial and marine bacterium were collected from pineapple agricultural lands, tropical rain forests, coastlands and mangrove swamps. Organisms were screened for activity using chromogenic substrates (AZCL Megazyme International Ltd., Ireland). The media composition for the effective culturing of some of the marine organisms has also been standardized. Gram-negative organisms were identified by sequence analysis of the PCR- amplified partial small subunit rRNA gene. Results indicate that the majority of the marine organisms tested belong to the genera Vibrio and Pseudoalteromonas and in the terrestrial environmentsChryseobacterium predominated. These experiments reveal that sub-tropical environments are potentially good sources of microorganisms with novel carbohydrase activities

Identification of carbohydrate degrading bacteria in sub-tropical regions.

Several bacteria from the islands of Puerto Rico, Vieques and Trinidad were isolated for their carbohydrate degrading activities. These terrestrial and marine bacterium were collected from pineapple agricultural lands, tropical rain forests, coastlands and mangrove swamps. Organisms were screened for activity using chromogenic substrates (AZCL Megazyme International Ltd., Ireland). The media composition for the effective culturing of some of the marine organisms has also been standardized. Gram-negative organisms were identified by sequence analysis of the PCR- amplified partial small subunit rRNA gene. Results indicate that the majority of the marine organisms tested belong to the genera Vibrio and Pseudoalteromonas and in the terrestrial environments Chryseobacterium predominated. These experiments reveal that sub-tropical environments are potentially good sources of microorganisms with novel carbohydrase activities.