Comparison of various microbial inocula for the efficient anaerobic digestion of Laminaria hyperborea.

BACKGROUND: The hydrolysis of seaweed polysaccharides is the rate limiting step in anaerobic digestion (AD) of seaweeds. Seven different microbial inocula and a mixture of these (inoculum 8) were therefore compared in triplicate, each grown over four weeks in static culture for the ability to degrade Laminaria hyperborea seaweed and produce methane through AD. RESULTS: All the inocula could degrade L. hyperborea and produce methane to some extent. However, an inoculum of slurry from a human sewage anaerobic digester, one of rumen contents from seaweed-eating North Ronaldsay sheep and inoculum 8 used most seaweed volatile solids (VS) (means ranged between 59 and 68% used), suggesting that these each had efficient seaweed polysaccharide digesting bacteria. The human sewage inoculum, an inoculum of anaerobic marine mud mixed with rotting seaweed and inoculum 8 all developed to give higher volumes of methane (means between 41 and 62.5 ml g-1 of seaweed VS by week four) ,compared to other inocula (means between 3.5 and 27.5 ml g-1 VS). Inoculum 8 also gave the highest acetate production (6.5 mmol g-1 VS) in a single-stage fermenter AD system and produced most methane (8.4 mL mmol acetate-1) in phase II of a two-stage AD system. CONCLUSIONS: Overall inoculum 8 was found to be the most efficient inoculum for AD of seaweed. The study therefore showed that selection and inclusion of efficient polysaccharide hydrolysing bacteria and methanogenic archaea in an inoculum offer increased methane productivity in AD of L. hyperborea. This inoculum will now being tested in larger scale (10L) continuously stirred reactors optimised for feed rate and retention time to determine maximum methane production under single-stage and two-stage AD systems.

The potential of bacteria isolated from ruminal contents of seaweed-eating North Ronaldsay sheep to hydrolyse seaweed components and produce methane by anaerobic digestion in vitro.

The production of methane biofuel from seaweeds is limited by the hydrolysis of polysaccharides. The rumen microbiota of seaweed-eating North Ronaldsay sheep was studied for polysaccharidic bacterial isolates degrading brown-seaweed polysaccharides. Only nine isolates out of 65 utilized >90% of the polysaccharide they were isolated on. The nine isolates (eight Prevotella spp. and one Clostridium butyricum) utilized whole Laminaria hyperborea extract and a range of seaweed polysaccharides, including alginate (seven out of nine isolates), laminarin and carboxymethylcellulose (eight out of nine isolates); while two out of nine isolates additionally hydrolysed fucoidan to some extent. Crude enzyme extracts from three of the isolates studied further had diverse glycosidases and polysaccharidase activities; particularly against laminarin and alginate (two isolates were shown to have alginate lyase activity) and notably fucoidan and carageenan (one isolate). In serial culture rumen microbiota hydrolysed a range of seaweed polysaccharides (fucoidan to a notably lesser degree) and homogenates of L. hyperborea, mixed Fucus spp. and Ascophyllum nodosum to produce methane and acetate. The rumen microbiota and isolates represent potential adjunct organisms or enzymes which may improve hydrolysis of seaweed components and thus improve the efficiency of seaweed anaerobic digestion for methane biofuel production.

Cases of emesis associated with bacterial contamination of an infant breakfast cereal product.

A commercial product for infants containing cereal mixed with dried infant formula was diagnosed as producing rapid projectile vomiting in two infants. Analysis of multiple samples of the cereal product revealed significant contamination with two spore-forming species, Bacillus subtilis and a strain of Bacillus cereus. The latter is the most likely cause of the emetic food poisoning, but we were unable to detect B. cereus emetic toxin. This raises the possibility of the cause being either a new cereulide-type toxin, or the bacterial load, in which case the presence of B. subtilis could have been a contributing factor.

Heat-stable toxin production by strains of Bacillus cereus, Bacillus firmus, Bacillus megaterium, Bacillus simplex and Bacillus licheniformis.

Strains of Bacillus cereus can produce a heat-stable toxin (cereulide). In this study, 101 Bacillus strains representing 7 Bacillus species were tested for production of heat-stable toxins. Strains of B. megaterium, B. firmus and B. simplex were found to produce novel heat-stable toxins, which showed varying levels of toxicity. B. cereus strains (18 out of 54) were positive for toxin production. Thirteen were of serovar H1, and it was of interest that some were of clinical origin. Two were of serovars 17B and 20, which are not usually implicated in the emetic syndrome. Partial purification of the novel B. megaterium, B. simplex and B. firmus toxins showed they had similar physical characteristics to the B. cereus emetic toxin, cereulide.

Detection of Listeria species in refrigerated chicken carcasses using Clearview tm and a modified conventional culture method

Avaliou-se a ocorrência de Listeria spp em carcaças refrigeradas de frango, comparando-se a metodologia convencional recomendada pelo FDA, modificada pela introdução de uma segunda etapa de enriquecimento antes do plaqueamento, e o método rápido ClearviewTM (Oxoid, UK, Ltd). Foram analisadas 48 carcaças de frango de diferentes marcas e supermercados de Florianópolis, Brasil. Listeria spp foi encontrada em 21 (43,7 per center) amostras. Através do método Clearview encontrou-se 17 (35,4 per center) amostras positivas para Listeria spp, das quais 11 (23 per center) eram L. monocytogenes, 4 (8.3 per center) L. innocua, 1 (2.1 per center) L. welshimeri e 1 (2.1 per center) L. seeligeri. Através do método convencional modificado obteve-se um total de 14 (29.2 per center) amostras positivas para Listeria spp, das quais 7 (14.6 per center per center) eram L. monocytogenes, 6 (12.5 per center) L. innocua e 1 (2.1 per center) L. seeligeri. Com o método Clearview + API Listeria, obteve-se resultados confirmados à nível de espécie em 115-139 h, e com o método convencional modificado + API Listeria os resultados foram obtidos em 120-160 h. No entanto, o método Clearview pode indicar a presença de Listeria spp em apenas 43 h. Os resultados obtidos pelos métodos utilizados mostraram-se moderadamente concordantes e não apresentaram diferença significativa num intervalo de confiança de 95 per center.