Endo- and exoglucanase activities in bacteria from mangrove sediment

Abstract

The mangrove ecosystem is an unexplored source for biotechnological applications. In this unique environment, endemic bacteria have the ability to thrive in the harsh environmental conditions (salinity and anaerobiosis), and act in the degradation of organic matter, promoting nutrient cycles. Thus, this study aimed to assess the cellulolytic activities of bacterial groups present in the sediment from a mangrove located in Ilha do Cardoso (SP, Brazil). To optimize the isolation of cellulolytic bacteria, enrichments in two types of culture media (tryptone broth and minimum salt medium), both supplemented with 5% NaCl and 1% of cellulose, were performed. Tests conducted with the obtained colonies showed a higher occurrence of endoglycolytic activity (33 isolates) than exoglycolytic (19 isolates), and the degradation activity was shown to be modulated by the presence of NaCl. The isolated bacteria were clustered by BOX-PCR and further classified on the basis of partial 16S rRNA sequences as Alphaproteobacteria, Gammaproteobacteria, Actinobacteria, Firmicutes or Bacteroidetes. Therefore, this study highlights the importance of studies focusing on the endemic species found in mangroves to exploit them as novel biotechnological tools for the degradation of cellulose.

Keywords: cellulose; endo-1,4-β-D-glucanase; exo-1,4-β-D-glucanase; salinity.

Figure 1

Cellulase production by the isolates in mangrove sediment under two salinity conditions. (a) The results are presented as an index of enzyme activity, calculated by dividing the diameter of the halo by the diameter of the colony. (b) Relationship between the activities in the two conditions. Values indicating an increase or decrease in the two halos are represented by the lines y = 2× and y = 0.5×, respectively. Additionally, the names of the isolates with activity modulated by salinity are presented.

Figure 2

Fingerprint analyses of the isolates by BOX-PCR from isolates obtained from enrichments in TSB with glucose (a), TSB with cellulose (b), MM with glucose (c), and MM with cellulose (d). Similarity clusters were determined by UPGMA based on a Pearson correlation analysis of densitometric curves. The names of the isolates used in the phylogenetic reconstruction are in bold, and prefixes Ed and Ex indicate those with endoglucanase and exoglucanase activities, respectively.

Figure 3

Phylogenetic relationships based on partial 16S gene sequences of bacterial isolates from mangrove sediment with the best matches from the databases (12, 27). The alignment was constructed by Mega 4.1 software (35) followed by clustering using neighbor joining and the Kimura-2 parameter. A bootstrap analysis was performed with 1,000 repetitions, and values indicate the percentage of clustering matching. The bar in the bottom of the figure scales the number of differences in base composition among the sequences.