Astrid E. Mars

PRIMARY PRODUCTION OF SEAGRASS BEDS IN SOUTH SULAWESI (INDONESIA) - A COMPARISON OF HABITATS, METHODS AND SPECIES

Primary production of tropical seagrass meadows was studied between April and August 1990 in South Sulawesi, Indonesia. Oxygen evolution studies in enclosures over seagrass vegetation revealed gross community production values between 900 and 4400 mg C m−2 day−1. Assumed community respiration ranged from 800 to 1800 mg C m−2 day−1 in non-vegetated areas and from 1400 to 5100 mg C m−2 day−1 for areas with varying amounts of seagrass. Benthic community respiration varied considerably in response to diurnal fluctuations in the dissolved oxygen concentration in the water column. Net production was small (less than 500 mg C m−2 day−1) and slightly negative on seven of 12 occasions. Light compensation points ranged from 50 to 340 μE m−2 s−1. Bell jar measurements revealed no significant differences in seagrass production between coastal and reef island habitats. Leaf marking experiments with Enhalus acoroides (L.f.) Royle revealed significantly higher leaf growth in a coastal muddy area (3.1 ± 0.8 cm per shoot day−1) than at an offshore sandy reef site (1.6 ± 0.5 cm per shoot day−1), but relative growth rates were comparable between the two habitats (0.019 ± 0.005 g g−1 leaf biomass (AFDW) day−1 and 0.012 ± 0.003 g g−1 AFDW day−1, respectively). Leaf marking and plastochrone interval methods revealed similar results for net leaf production in a monospecific stand of Thalassia hemprichii (Ehrenb.) Aschers. at a reef site which averaged 1.6 g C m−2 day−1. Rhizome tagging experiments revealed net rhizome production values of 0.1−0.3 g C m−2 day−1 for Thalassia hemprichii at this reef site. Relative growth rate of leaves of Thalassia hemprichii (0.039 ± 0.010 g g−1 AFDW day−1) at the reef site was significantly higher than that of E. acoroides (0.012 ± 0.003 g g−1 AFDW day−1). The pioneering seagrass species Halodule uninervis (Forssk.) Aschers. and Cymodocea rotundata Ehrenb. & Hempr. ex Aschers. had considerably higher horizontal apical rhizome growth rates (0.7–0.9 cm per apex day−1) than the constant species Thalassia hemprichii (0.1 cm per apex day−1). The suitability of different methods to measure seagrass productivity is evaluated.

Overproduction of Heterologous Mannitol 1-Phosphatase: a Key Factor for Engineering Mannitol Production by Lactococcus lactis

ABSTRACT To achieve high mannitol production by Lactococcus lactis, the mannitol 1-phosphatase gene of Eimeria tenella and the mannitol 1-phosphate dehydrogenase gene mtlD of Lactobacillus plantarum were cloned in the nisin-dependent L. lactis NICE overexpression system. As predicted by a kinetic L. lactis glycolysis model, increase in mannitol 1-phosphate dehydrogenase and mannitol 1-phosphatase activities resulted in increased mannitol production. Overexpression of both genes in growing cells resulted in glucose-mannitol conversions of 11, 21, and 27% by the L. lactis parental strain, a strain with reduced phosphofructokinase activity, and a lactate dehydrogenase-deficient strain, respectively. Improved induction conditions and increased substrate concentrations resulted in an even higher glucose-to-mannitol conversion of 50% by the lactate dehydrogenase-deficient L. lactis strain, close to the theoretical mannitol yield of 67%. Moreover, a clear correlation between mannitol 1-phosphatase activity and mannitol production was shown, demonstrating the usefulness of this metabolic engineering approach.

Metabolic Engineering of Mannitol Production in Lactococcus lactis: Influence of Overexpression of Mannitol 1-Phosphate Dehydrogenase in Different Genetic Backgrounds

ABSTRACT To obtain a mannitol-producing Lactococcus lactis strain, the mannitol 1-phosphate dehydrogenase gene (mtlD) from Lactobacillus plantarum was overexpressed in a wild-type strain, a lactate dehydrogenase(LDH)-deficient strain, and a strain with reduced phosphofructokinase activity. High-performance liquid chromatography and 13C nuclear magnetic resonance analysis revealed that small amounts (<1%) of mannitol were formed by growing cells of mtlD-overexpressing LDH-deficient and phosphofructokinase-reduced strains, whereas resting cells of the LDH-deficient transformant converted 25% of glucose into mannitol. Moreover, the formed mannitol was not reutilized upon glucose depletion. Of the metabolic-engineering strategies investigated in this work, mtlD-overexpressing LDH-deficient L. lactis seemed to be the most promising strain for mannitol production.

Detoxification of reactive intermediates during microbial metabolism of halogenated compounds

The reactivity and toxicity of metabolic intermediates that are generated by initial biotransformation reactions can be a major limiting factor for biodegradation of halogenated organic compounds. Recent work on the conversion of haloalkanes, chloroaromatics and chloroethenes indicates that microorganisms may become less sensitive to toxic effects either by using novel pathways that circumvent the generation of reactive intermediates or by producing modified enzymes that decrease the toxicity of such compounds.

Microbial Degradation of Chlorinated Aromatic Compounds

The aerobic microbial degradation of various chloroaromatics usually occurs via chlorocatechols as central intermediates. These are further degraded through the modified ortho-cleavage pathway. Dechlorination takes place during cycloisomerization of chloromuconates and reduction of chloromaleylacetates. In contrast, the degradation of haloaromatics via meta-cleavage was thought to be impossible due to toxicity of cleavage intermediates, whereas the meta route is more effective for methylaromatics. Recently, Pseudomonas putida strain GJ31 was shown to be able to degrade toluene and chlorobenzene simultaneously. Strain GJ31 rapidly degrades chlorobenzene via 3-chlorocatechol using the meta-cleavage pathway without any apparent toxic effects. An unusual chlorocatechol 2,3-dioxygenase oxidizes 3-chlorocatechol. Stoichiometric displacement of chloride then leads to the production of 2-hydroxymuconate, which is a common metabolite of the meta-cleavage pathway. In contrast to other catechol 2,3-dioxgenases, which are subject to inactivation when exposed to 3-chlorocatechol, the chlorocatechol 2,3-dioxygenase is resistant. The gene encoding the chlorocatechol 2,3-dioxygenase (cbzE) of strain GJ31 was cloned and sequenced. CbzE was most similar to catechol 2,3-dioxygenases of the 2.C subfamily of type 1 extradiol dioxygenases. Hybrid enzymes, which were made of CbzE and the 3-methylcatechol 2,3-dioxygenase of strain P. putida UCC2, showed that the resistance of CbzE to suicide inactivation and the substrate specificity were mainly determined by the C-terminal region of the protein. Establishing whether the meta-cleavage pathway of strain GJ31 can function as pathway segment in the construction of novel chloroaromatics-degraders is a future task. Organisms such as P. putida strain GJ31 and its derivatives may be useful for effective treatment of waste streams containing various methyl- and chloroaromatics.