The Microbial Community of Grape Berry - Part 2

In the previous blog, The Microbial Community of Grape Berry, the topic was about the four groups of microorganisms that include (1) residents, (2) adventitious, (3) invaders, and (4) opportunists that can populate the grape berry. This is Part 2 on the topic of the microbial community of the grape berry.
In this blogpost, I will take a closer look at the grape berry and in particular, the skin also called epidermis and/or cuticle.²

The grape berry cuticle is comprised of:

• the insoluble cutin, a chloroform-insoluble complex polymer consisting mostly of C16 or C18 ω-hydroxylated esterified fatty acids, the major structural component matrix
• a mixture of waxes: the intracuticular waxes, which infiltrate the cutin framework, and a thin amorphous epicuticular wax layer which accumulates on the surface and is composed of a very complex mixture of long-chain lipids
• the major components of cutin are C16 and C18 fatty acid esters
• the composition of the cuticular waxes changes during the period from flowering to maturity, revealing an increase in waxy deposits and significant modifications on the wax surface morphology
• differentiation of the cuticle layers and a decrease in the thickness of the primary cuticle is further detected at harvest leading to the susceptibility of ripe grapes to B. cinerea infection
• during the final stage of growth, the berry surface is smooth, continuous and homogenous, with a 3 μm thick cuticle

The grape berry cuticle plays several important roles:

• constitutes a physical barrier between the external environment and the inner tissues
• provides protection against biotic and abiotic stresses
• are metabolically active during development and ripening
• exhibit endocrinal function
• during the early stages of infection can act as elicitors of plant defense responses
• may dissolve and retain some isoprenoid volatile organic compounds released by grapes – a potential nutrient carbon source for the berry microbiota, particularly the resident community

We now know the microbial community present on the grape berry, a bit more about the cuticle surface that these microbes live on and the function of the cuticle. Stay tuned for further blogs on the "Microbial Community of the Grape Berry".
References:
1. V. Loureiro, M. M. Ferreira1, S. Monteiro1 and R. B. Ferreira, "The Microbial Community of Grape Berry", The Biochemistry of the Grape Berry, Chapter 12, 2012, 241-268.
2. Dunsford, P.A. and Sneyd, T.N., "Pressing for quality", Proceedings of the Seventh Australian Wine Industry Technical Conference.