Flavobacterium hibernum sp. nov., a lactose-utilizing bacterium from a freshwater Antarctic Lake

Abstract

Four freshwater Antarctic lakes were examined for the presence of pgalactosidase-producing bacteria using mineral medium enrichments and lactose. Enrichments from only one of the lakes produced growth and two strains were isolated that were very similar in phenotype and fatty acid profile, and shared considerable homology in their DNA (DNA-DNA hybridization = 9327 YO). The strains were psychrotrophic with theoretical T,,,,,, Tmin and To,, of 30-31, -7 O and 26 "C, respectively. The P-galactosidase in cell extracts had an optimal activity at 39 "C. The strains were Gram-negative rods, showed gliding motility, contained branched and hydroxy fatty acids, and menaquinone 6 as the major respiratory quinone. The strains did not form microcysts and utilized lactose while using ammonium ions as a source of nitrogen, and a range of other sugars. The G+C content of the DNA was 34 mol%. Phylogenetic analysis of one of the strains, by comparison of 165 rDNA sequences, showed that it was most similar, but not identical to, Flavobacterium columnare and [Sporocytophaga] cauliformis '. Both species could be differentiated phenotypically from the Antarctic isolates. DNA-DNA hybridization of the Antarctic isolate with six different members of the Flavobacterium 165 rDNA cluster showed no strain with greater than 18% relatedness. The nearest type species to the Antarctic isolate in the phylogenetic analysis was Flavobacterium aquatile. The name Flavobacterium hibernum is proposed for the Antarctic strains, and the type strain is ATCC 51468T (= ACAM 376T).Keywords: Flavobacterium hibernum, psychrotroph, P-galactosidase, Antarctica INTRODUCTIONMany humans are intolerant to lactose in their diet and as a result are unable to consume unfermented dairy products without considerable discomfort. One technological approach to solving this problem is to use bgalactosidase in the processing of dairy foods. However, the optimal temperatures for hydrolysis of lactose by P-galactosidases range between 30 and 40 OC, which is also the ideal temperature range for the growth of mesophiles that contaminate and spoil dairy products (Gounot, 1991). Hydrolysis of lactose at low temperatures may be a viable option if a psychrophile can be isolated that produces an efficient low-temperature b-galactosidase (Gounot, 199 1).As part of an ongoing study on the microbial diversity of Antarctic ecosystems, and due to the possible benefits arising from the isolation of psychrophilic j?-galactosidase-producing strains, we targeted lactoseutilizing strains from a number of freshwater Antarctic lakes for enrichment and isolation. A taxonomic study of the isolates was undertaken and the work is herein described. Isolation of bacterial strains. Four freshwater Antarctic lakes [conductivity (pS cm-') and pH given in parentheses after each name] : Druzhby Lake (29,7*2), Crooked Lake (26,7.1), Pauk Lake (118, 7-0) and Lichen Lake (73, 7.3), were sampled for lactose-utilizing bacteria. Each lake was sampled twice, at the same hour from sample points within 10 m of each...

Taxonomy of Antarctic Flavobacterium species: description of Flavobacterium gillisiae sp. nov., Flavobacterium tegetincola sp. nov., and Flavobacterium xanthum sp. nov., nom. rev. and reclassification of [Flavobacterium] salegens as Salegentibacter salegens gen. nov., comb. nov.

“…Growth at 25 mC on agar (j) (j) (j) j j j j j k j j j j j Gliding motility k j k j j j k j (j) j j j j j Flexirubins k k k k j k k j j j j j j k Glucose utilization j j j j j   k k j j j j j Acid from carbohydrates j j j j j j j k k j j j j j Bernardet et al (1996), McCammon et al (1998) and this study.…”

“…Lactose-utilizing isolates from a highly oligotrophic freshwater lake in the Vestfold Hills were described as Flavobacterium hibernum by McCammon et al (1998). Finally a number of yellow-and orange-pigmented isolates from sea ice and marine salinity lake samples (Franzmann et al, 1990 ;Bowman et al, 1997a) have been found to be phylogenetically related to the genus Flavobacterium ; however 16S rRNA sequence data suggested these strains represent potentially novel species.…”

Flavobacterium rakeshii sp. nov., isolated from marine sediment, and emended description of Flavobacterium beibuense Fu et al. 2011

“…At present, the genus comprises more than 69 species with validly published names, with Flavobacterium aquatile as the type species. Members of the genus have been isolated from various habitats, such as freshwater (Wang et al, 2006;Tamaki et al, 2003), soil (Bernardet et al, 1996;Tamaki et al, 2003;McCammon & Bowman, 2000;Liu et al, 2008), glacier (Zhu et al, 2003), Antarctic lakes (Van Trappen et al, 2003, 2004McCammon et al, 1998;McCammon & Bowman, 2000;Humphry et al, 2001;Yi et al, 2005) and marine sediments (Fu et al, 2011). In addition, three Flavobacterium species are pathogenic to fish (Bernardet & Bowman, 2006).…”

Flavobacterium lacus sp. nov., isolated from a high-altitude lake, and emended description of Flavobacterium filum

“…Owing to the continuous exploration of extreme environments, the genus has expanded considerably, especially with psychrophilic and psychrotolerant species. Among published species of the genus Flavobacterium, 25 are coldadapted organisms, of which 14 were isolated from the Antarctic (Humphry et al, 2001;McCammon & Bowman, 2000;McCammon et al, 1998;Van Trappen et al, 2003Yi & Chun, 2006;Yi et al, 2005) and eight from glaciers in China (Dong et al, 2012; Xin et al, 2009; Xu et al, 2011;Zhang et al, 2006;Zhu et al, 2003Zhu et al, , 2013.Strains NP180 T and NR80 were isolated from Nam Co lake located in Tibet in the west of China, at an altitude of 4718 m (30 u 309 N 90 u 169 E); the annual mean water temperature is 10-15 u C. Samples of lake water were collected and 10-fold dilutions were plated on PYG agar (5.0 g Bacto peptone, 0.2 g yeast extract, 5.0 g glucose, 3.0 g beef extract, 0.5 g NaCl, 1. 1000 ml sterile water, 15 g agar, pH 7.0).…”