Janneke Krooneman

Anaerobic Conversion of Lactic Acid to Acetic Acid and 1,2-Propanediol by Lactobacillus buchneri

ABSTRACT The degradation of lactic acid under anoxic conditions was studied in several strains of Lactobacillus buchneri and in close relatives such as Lactobacillus parabuchneri,Lactobacillus kefir, and Lactobacillus hilgardii. Of these lactobacilli, L. buchneri andL. parabuchneri were able to degrade lactic acid under anoxic conditions, without requiring an external electron acceptor. Each mole of lactic acid was converted into approximately 0.5 mol of acetic acid, 0.5 mol of 1,2-propanediol, and traces of ethanol. Based on stoichiometry studies and the high levels of NAD-linked 1,2-propanediol-dependent oxidoreductase (530 to 790 nmol min−1 mg of protein−1), a novel pathway for anaerobic lactic acid degradation is proposed. The anaerobic degradation of lactic acid by L. buchneri does not support cell growth and is pH dependent. Acidic conditions are needed to induce the lactic-acid-degrading capacity of the cells and to maintain the lactic-acid-degrading activity. At a pH above 5.8 hardly any lactic acid degradation was observed. The exact function of anaerobic lactic acid degradation by L. buchneri is not certain, but some results indicate that it plays a role in maintaining cell viability.

Lactobacillus diolivorans sp nov., a 1,2-propanediol-degrading bacterium isolated from aerobically stable maize silage

Inoculation of maize silage with Lactobacillus buchneri (5 x 10(5) c.f.u. g(-1) of maize silage) prior to ensiling results in the formation of aerobically stable silage. After 9 months, lactic acid bacterium counts are approximately 10(10) c.f.u. g(-1) in these treated silages. An important subpopulation (5.9 x 10(7) c.f.u. g(-1)) is able to degrade 1,2-propanediol, a fermentation product of L. buchneri, under anoxic conditions to 1-propanol and propionic acid. From this group of 1,2-propanediol-fermenting, facultatively anaerobic, heterofermentative lactobacilli, two rod-shaped isolates were purified and characterized. Comparative 16S rDNA sequence analysis revealed that the newly isolated bacteria have identical 16S rDNA sequences and belong phylogenetically to the L. buchneri group. DNA-DNA hybridizations, whole-cell protein fingerprinting and examination of phenotypic properties indicated that these two isolates represent a novel species, for which the name Lactobacillus diolivorans sp. nov. is proposed. The type strain is LMG 19667T (= DSM 14421T).

Identity, abundance and ecophysiology of filamentous bacteria belonging to the Bacteroidetes present in activated sludge plants

Filamentous members of the Bacteroidetes are commonly observed in activated sludge samples originating from both municipal and industrial wastewater treatment plants (WWTP), where they occasionally can cause bulking. Several oligonucleotide 16S rRNA-targeted probes were designed to target filaments with a needle-like appearance similar to Haliscomenobacter hydrossis. The design of these probes was based on an isolate and a sequence obtained from a micromanipulated filament. The abundance of filamentous Bacteroidetes was determined in 126 industrial samples applying already published and the newly developed probes. Small populations were found in 62 % of the WWTP investigated. However, only relatively few WWTP (13 %) contained large populations of filamentous Bacteroidetes potentially responsible for bulking incidences. The identity of the most abundant filamentous Bacteroidetes with H. hydrossis morphology could be detected by probes CFB719, SAP-309 and the newly designed probe HHY-654. A comprehensive study on the ecophysiology of probe-defined Bacteroidetes populations was conducted on Danish and Czech samples. The studies revealed that they were specialized bacteria involved in degradation of sugars, e.g. glucose and N-acetylglucosamine, and may participate in the conversion of lipopolysaccharides and peptidoglycan liberated by decaying cells. Many surface-associated exo-enzymes were excreted, e.g. chitinase, glucuronidase, esterase and phosphatase, supporting conversion of polysaccharides and possibly other released cell components. The role of filamentous bacteria with a H. hydrossis-like morphology in the activated sludge ecosystem is discussed.

Clostridium acetireducens sp. nov., a novel amino acid-oxidizing, acetate-reducing anaerobic bacterium

Strain 30AT (T = type strain), which was isolated from an anaerobic bioreactor fed on waste from a potato starch factory in De Krim, The Netherlands, is a nonmotile, gram-positive, anaerobic, rod-shaped organism that is able to degrade various amino acids, including alanine, leucine, isoleucine, valine, serine, and threonine. Acetate is required as an electron acceptor for the utilization of alanine, valine, leucine, and isoleucine. Other growth substrates, including pyruvate, a-ketobutyrate, a-ketoisocaproate, cu-keto-3-methylvalerate, a-ketoisovalerate, and peptone, are intermediates in amino acid catabolism. Strain 30AT utilizes neither the branched-chain amino acids nor alanine via interspecies hydrogen transfer with methanogenic and sulfatereducing bacteria or via the Stickland reaction with proline or glycine as an electron acceptor. No growth occurs with the following electron acceptors: fumarate, nitrate, nitrite, sulfite, sulfate, and oxygen. Yeast extract is required for growth. Sugars are not degraded. The optimal temperature and optimal pH for growth are 39 to 43°C and 6.4 to 7.6, respectively. The results of a 16s rRNA sequence analysis phylogenetically placed strain 30AT in Clostridium group I (genus Clostridium sensu stricto), where it forms a new and distinct line of descent.

Microbial detection and monitoring in advanced life support systems like the International Space Station

Potentially pathogenic microbes and so-called technophiles may form a serious threat in advanced life support systems, such as the International Space Station (ISS). They not only pose a threat to the health of the crew, but also to the technical equipment and materials of the space station. The development of fast and easy to use molecular detection and quantification methods for application in manned spacecraft is therefore desirable and may also be valuable for applications on Earth. In this paper we present the preliminary results of the SAMPLE experiment in which we performed molecular microbial analysis on environmental samples of the ISS as part of an ESA-MAP project.

The Role of Environmental Conditions and Biotic Interactions Between Microbial Species in Degradation of Chlorinated Pollutants

Degradation of chlorinated aromatic and aliphatic organic compounds in natural environments depends on the interplay of a multitude of both abiotic and biotic factors. Hence the extent and rate of these processes can only be understood if, in addition to monitoring the individual microbial processes under the prevailing environmental conditions, detailed knowledge of the interactions between the various physiologically different microbial populations is obtained as well.