Open Access Highly Accessed Research article

Proteins of novel lactic acid bacteria from Apis mellifera mellifera: an insight into the production of known extra-cellular proteins during microbial stress

Èile Butler1, Magnus Alsterfjord1, Tobias C Olofsson1, Christofer Karlsson23, Johan Malmström2 and Alejandra Vásquez1*

Author Affiliations

1 Medical Microbiology, Department of Laboratory Medicine, Lund University, Sölvegatan 23, Lund SE-223 62, Sweden

2 Department of Immunotechnology, Lund University BMC D13, Lund SE-221 84, Sweden

3 Division of Infection Medicine, Department of Clinical Sciences, Lund University, BMC, B14, Lund 221 84, Sweden

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BMC Microbiology 2013, 13:235  doi:10.1186/1471-2180-13-235

Published: 22 October 2013

Abstract

Background

Lactic acid bacteria (LAB) has been considered a beneficial bacterial group, found as part of the microbiota of diverse hosts, including humans and various animals. However, the mechanisms of how hosts and LAB interact are still poorly understood. Previous work demonstrates that 13 species of Lactobacillus and Bifidobacterium from the honey crop in bees function symbiotically with the honeybee. They protect each other, their hosts, and the surrounding environment against severe bee pathogens, bacteria, and yeasts. Therefore, we hypothesized that these LAB under stress, i.e. in their natural niche in the honey crop, are likely to produce bioactive substances with antimicrobial activity.

Results

The genomic analysis of the LAB demonstrated varying genome sizes ranging from 1.5 to 2.2 mega-base pairs (Mbps) which points out a clear difference within the protein gene content, as well as specialized functions in the honeybee microbiota and their adaptation to their host. We demonstrate a clear variation between the secreted proteins of the symbiotic LAB when subjected to microbial stressors. We have identified that 10 of the 13 LAB produced extra-cellular proteins of known or unknown function in which some are arranged in interesting putative operons that may be involved in antimicrobial action, host interaction, or biofilm formation. The most common known extra-cellular proteins secreted were enzymes, DNA chaperones, S-layer proteins, bacteriocins, and lysozymes. A new bacteriocin may have been identified in one of the LAB symbionts while many proteins with unknown functions were produced which must be investigated further.

Conclusions

The 13 LAB symbionts likely play different roles in their natural environment defending their niche and their host and participating in the honeybee’s food production. These roles are partly played through producing extracellular proteins on exposure to microbial stressors widely found in natural occurring flowers. Many of these secreted proteins may have a putative antimicrobial function. In the future, understanding these processes in this complicated environment may lead to novel applications of honey crop LAB proteins.

Keywords:
Lactic acid bacteria; Symbionts; Microbial stress; Proteomics; Honeybee