Growth kinetics and competition — some contemporary comments

Results of competition experiments with one growth-limiting factor under idealized experimental conditions have been reported extensively, and usually provide ample support for the conclusion that 'complete competitors cannot coexist'. However, under conditions of multiple substrate limitation and discontinuous or alternating supply of nutrients, coexistence of species is quite common. Since such patterns of nutrient supply may be expected to prevail in many natural environments the mechanisms ruling the survival and growth of bacteria under such conditions need to be understood. However, it appears that surprisingly little is known of the physiological state of individual competing species grown in mixed cultures. Unfortunately, basic information such as the actual concentration of limiting nutrients is lacking in most cases. But perhaps the recent development of new and powerful techniques to explore the physiological properties even of individual cells will further stimulate studies into the mechanisms behind the competitiveness of microbial species

The effect of oxygen and sulfhydryl reagents on the hydrolysis and the fermentation of chitin by Clostridium 9.1

Inhibition experiments employing sulfhydryl binding and sulfhydryl oxidizing reagents showed the presence of essential thiol groups in the chitinolytic system of Clostridium 9.1. Inhibition of fermentation by membrane-impermeable reagents was relieved upon addition of excess reductant, suggesting the involvement of essential thiol groups in sugar transport activity. The chitinolytic system and the fermentation of the bacterium appeared relatively insensitive to oxyge

Growth of a facultative anaerobe under oxygen‐limiting conditions in pure culture and in co‐culture with a sulfate‐reducing bacterium

The occurrence and properties were studied of glucose‐metabolizing bacteria present in the anaerobic sediment 5–10 cm below the surface of an estuarine tidal mud‐flat. Of all these bacteria (104– 105 per g wet sediment) 80–90% were facultatively anaerobic species. Chemostat enrichments on glucose under aerobic, oxygen‐limited and alternately aerobic‐anaerobic conditions also yielded cultures dominated by facultative anaerobes. One of the dominant species, tentatively identified as a Vibrio sp., was studied in more detail under oxygen‐limiting conditions. Fermentative and respiratory metabolisms were found to operate simultaneously, and the ratio between the two was regulated by the extent of oxygen limitation. A small fraction of the acetate formed under such growth conditions was shown to be subsequently respired. A co‐culture was established of the Vibrio sp. and a sulfate‐reducing bacterium (Desulfovibrio HL21 ) in an aerated chemostat. The importance of these observations is discussed in relation to the role of facultative anaerobes in anaerobic habitats

Mixed chemostat cultures of obligately aerobic and fermentative or methanogenic bacteria grown under oxygen-limiting conditions

Defined mixed cultures of an obligately aerobic Pseudomonas testosteroni and anaerobic Veillonella alcalescens strain were grown under oxygen and lactate limitation in chemostats with different oxygen supply rates. The aerobic and the anaerobic bacteria were shown to coexist and to complete for common substrates over a wide range of oxygen supply rates. Under similar conditions but with formate as the major substrate chemostat enrichments gave rise to undefined mixed cultures of aerobic, fermentative and methanogenic bacteria. The relevance of these observations to natural mineralization processes is discussed

Selective enrichment of facultatively chemolithotrophic thiobacilli and related organisms in continuous culture

The current opinion is that facultatively chemo-lithotrophic thiobacilli, sometimes referred to as “versatile ” thiobacilli [ 11, often may have a signifi-cant ecological advantage over their more specialize

Properties of Desulfovibrio carbinolicus sp. nov. and Other Sulfate-Reducing Bacteria Isolated from an Anaerobic-Purification Plant

Several sulfate-reducing microorganisms were isolated from an anaerobic-purification plant. Four strains were classified as Desulfovibrio desulfuricans, Desulfovibrio sapovorans, Desulfobulbus propionicus, and Desulfovibrio sp. The D. sapovorans strain contained poly-β-hydroxybutyrate granules and seemed to form extracellular vesicles. A fifth isolate, Desulfovibrio sp. strain EDK82, was a gram-negative, non-spore-forming, nonmotile, curved organism. It was able to oxidize several substrates, including methanol. Sulfate, sulfite, thiosulfate, and sulfur were utilized as electron acceptors. Pyruvate, fumarate, malate, and glycerol could be fermented. Because strain EDK82 could not be ascribed to any of the existing species, a new species, Desulfovibrio carbinolicus, is proposed. The doubling times of the isolates were determined on several substrates. Molecular hydrogen, lactate, propionate, and ethanol yielded the shortest doubling times (3.0 to 6.3 h). Due to the presence of support material in an anaerobic filter system, these species were able to convert sulfate to sulfide very effectively at a hydraulic retention time as short as 0.5 h

Specific removal of chlorine from the ortho-position of halogenated benzoic acids by reductive dechlorination in anaerobic enrichment cultures

Anaerobic enrichment cultures catalysing the reductive dechlorination of chlorinated benzoic acids were obtained from three fresh-water sediments collected from seven different locations. Sub-cultures from these enrichments specifically removed ortho-substituted chlorine from 2,3,6-, 2,3,5- and 2,4,6-trichlorobenzoic acid, yielding chloride and 2,5-, 3,5-, and 2,4-dichlorobenzoic acids, respectively. These reductive dehalogenations were stimulated by the addition of benzoate and/or volatile organic acids. In one of these enrichments dehalogenation of ortho- and/or para-chlorine substituents was also observed from 2,3-, 2,4-, 2,5-, and 3,4-dichlorobenzoic acid, yielding 3- and 4-chlorobenzoate. Removal of meta-chlorines was not observed in any of the enrichments