Carbazole degradation in the soil microcosm by tropical bacterial strains

In a previous study, three bacterial strains isolated from tropical hydrocarbon-contaminated soils and phylogenetically identified as Achromobacter sp. strain SL1, Pseudomonas sp. strain SL4 and Microbacterium esteraromaticum strain SL6 displayed angular dioxygenation and mineralization of carbazole in batch cultures. In this study, the ability of these isolates to survive and enhance carbazole degradation in soil were tested in field-moist microcosms. Strain SL4 had the highest survival rate (1.8 x 107 cfu/g) after 30 days of incubation in sterilized soil, while there was a decrease in population density in native (unsterilized) soil when compared with the initial population. Gas chromatographic analysis after 30 days of incubation showed that in sterilized soil amended with carbazole (100 mg/kg), 66.96, 82.15 and 68.54% were degraded by strains SL1, SL4 and SL6, respectively, with rates of degradation of 0.093, 0.114 and 0.095 mg kg−1 h−1. The combination of the three isolates as inoculum in sterilized soil degraded 87.13% carbazole at a rate of 0.121 mg kg−1 h−1. In native soil amended with carbazole (100 mg/kg), 91.64, 87.29 and 89.13% were degraded by strains SL1, SL4 and SL6 after 30 days of incubation, with rates of degradation of 0.127, 0.121 and 0.124 mg kg−1 h−1, respectively. This study successfully established the survivability (> 106 cfu/g detected after 30 days) and carbazole-degrading ability of these bacterial strains in soil, and highlights the potential of these isolates as seed for the bioremediation of carbazole-impacted environments.

New host record of five Flavobacterium species associated with tropical fresh water farmed fishes from North India

Abstract Yellow pigmented, filamentous, Gram-negative bacteria belonging to genus Flavobacterium are commonly associated with infections in stressed fish. In this study, inter-species diversity of Flavobacterium was studied in apparently healthy freshwater farmed fishes. For this, ninety one yellow pigmented bacteria were isolated from skin and gill samples (n = 38) of three farmed fish species i.e. Labeo rohita, Catla catla and Cyprinus carpio. Among them, only twelve bacterial isolates (13.18%) were identified as Flavobacterium spp. on the basis of morphological, biochemical tests, partial 16S rDNA gene sequencing and phylogenetic analysis. On the basis of 16S rDNA gene sequencing, all the 12 isolates were 97.6-100% similar to six different formally described species of genus Flavobacterium. The 16S rDNA based phylogenetic analysis grouped these strains into six different clades. Of the 12 isolates, six strains (Fl9S1-6) grouped with F. suncheonense, two strains (Fl6I2, Fl6I3) with F. indicum and the rest four strains (Fl1A1, Fl2G1, Fl3H1 and Fl10T1) clustered with F. aquaticum, F. granuli, F. hercynium and F. terrae, respectively. None of these species except, F. hercynium were previously reported from fish. All the isolated Flavobacterium species possessed the ability of adhesion and biofilm formation to colonize the external surface of healthy fish. The present study is the first record of tropical freshwater farmed fishes as hosts to five environmentally associated species of the Flavobacterium.

Screening and characterization of endophytic Bacillus and Paenibacillus strains from medicinal plant Lonicera japonica for use as potential plant growth promoters

Abstract A total of 48 endophytic bacteria were isolated from surface-sterilized tissues of the medicinal plant Lonicera japonica, which is grown in eastern China; six strains were selected for further study based on their potential ability to promote plant growth in vitro (siderophore and indoleacetic acid production). The bacteria were characterized by phylogenetically analyzing their 16S rRNA gene similarity, by examining their effect on the mycelial development of pathogenic fungi, by testing their potential plant growth-promoting characteristics, and by measuring wheat growth parameters after inoculation. Results showed that the number of endophytic bacteria in L. japonica varied among different tissues, but it remained relatively stable in the same tissues from four different plantation locations. Among the three endophytic strains, strains 122 and 124 both had high siderophore production, with the latter showing the highest phosphate solubilization activity (45.6 mg/L) and aminocyclopropane-1-carboxylic acid deaminase activity (47.3 nmol/mg/h). Strain 170 had the highest indoleacetic acid (IAA) production (49.2 mg/L) and cellulase and pectinase activities. After inoculation, most of the six selected isolates showed a strong capacity to promote wheat growth. Compared with the controls, the increase in the shoot length, root length, fresh weight, dry weight, and chlorophyll content was most remarkable in wheat seedlings inoculated with strain 130. The positive correlation between enzyme (cellulose and pectinase) activity and inhibition rate on Fusarium oxysporum, the IAA production, and the root length of wheat seedlings inoculated with each tested endophytic strain was significant in regression analysis. Deformity of pathogenic fungal mycelia was observed under a microscope after the interaction with the endophytic isolates. Such deformity may be directly related to the production of hydrolytic bacterial enzymes (cellulose and pectinase). The six endophytic bacterial strains were identified to be Paenibacillus and Bacillus strains based on the results of 16S rRNA gene sequencing analysis and their physiological and biochemical characteristics. Results indicate the promising application of endophytic bacteria to the biological control of pathogenic fungi and the improvement of wheat crop growth.